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Preview: Journal of Antimicrobial Chemotherapy - current issue

Journal of Antimicrobial Chemotherapy Current Issue





Published: Fri, 08 Sep 2017 00:00:00 GMT

Last Build Date: Mon, 23 Oct 2017 10:48:58 GMT

 






Effect of β-lactamase production and β-lactam instability on MIC testing results for Mycobacterium abscessus

2017-09-08

Abstract
Objectives
Limited treatment options available for Mycobacterium abscessus infections include the parenteral β-lactam antibiotics cefoxitin and imipenem, which show moderate in vitro activity. Other β-lactam antibiotics (except meropenem) have no considerable in vitro activity, due to their rapid hydrolysis by a broad-spectrum β-lactamase (Bla_Mab). We here addressed the impact of β-lactamase production and β-lactam in vitro stability on M. abscessus MIC results and determined the epidemiological cut-off (ECOFF) values of cefoxitin, imipenem and meropenem.
Methods
By LC high-resolution MS (LC-HRMS), we assessed the in vitro stability of cefoxitin, imipenem and meropenem. M. abscessus ATCC 19977 strain and its isogenic blaMab deletion mutant were used for MIC testing. Based on MIC distributions for M. abscessus clinical strains, we determined ECOFFs of cefoxitin, imipenem and meropenem.
Results
A functional Bla_Mab increased MICs of penicillins, ceftriaxone and meropenem. LC-HRMS data showed significant degradation of cefoxitin, imipenem and meropenem during standard antibiotic susceptibility testing procedures. MIC, MIC50 and ECOFF values of cefoxitin, imipenem and meropenem are influenced by incubation time.
Conclusions
The results of our study support administration of imipenem, meropenem and cefoxitin, for treatment of patients infected with M. abscessus. Our findings on in vitro instability of imipenem, meropenem and cefoxitin explain the problematic correlation between in vitro susceptibility and in vivo activity of these antibiotics and question the clinical utility of susceptibility testing of these chemotherapeutic agents.



Penetration and antiviral efficacy of total and unbound maraviroc, raltegravir and rilpivirine in both female and male genital fluids from HIV-positive patients receiving regimens containing these antiretrovirals

2017-09-08

Abstract
Background
Sub-optimal penetration of antiretroviral drugs in genital compartments might promote local HIV persistence and increase the risk of HIV transmission.
Objectives
To describe the penetration of maraviroc, raltegravir, raltegravir glucuronide and rilpivirine in seminal plasma and cervico-vaginal secretions (CVS) and to assess local antiretroviral efficacy in HIV-1-positive patients.
Methods
This was a prospective, multicentre study. Inclusion criteria were HIV-1 positive, age >18 years, receiving regimens containing maraviroc and/or raltegravir and/or rilpivirine for >1 month, and good self-reported adherence. Paired blood and genital samples were collected 12 h (raltegravir and maraviroc) or 24 h (rilpivirine) post-dose. These concentrations were determined (UPLC–MS/MS) in blood and seminal plasma (total and unbound) and CVS (total, dried spots) and HIV-RNA was quantified in paired blood and genital samples.
Results
Among the 54 enrolled patients, 15 received maraviroc (6 men), 27 received raltegravir (14 men) and 20 received rilpivirine (10 men), corresponding to 54 total and 52 unbound plasma concentrations, 29 total CVS samples and 23 total and 18 unbound seminal plasma samples. Maraviroc and raltegravir displayed a ratio of genital fluids/plasma concentrations >0.5 in both male and female genital tracts. Conversely, rilpivirine displayed a low ratio. Antiretroviral free fractions were consistent with historical data. Nine patients had blood plasma HIV-RNA >50 copies/mL (2/9 had sub-optimal antiretroviral blood plasma exposure) and two other patients had detectable HIV-RNA in genital fluids.
Conclusions
Maraviroc and raltegravir demonstrated good penetration in genital compartments, yielding good local virological response in genital compartments, whereas rilpivirine presented a low penetration profile but good local response.



Visceral leishmaniasis relapse hazard is linked to reduced miltefosine exposure in patients from Eastern Africa: a population pharmacokinetic/pharmacodynamic study

2017-09-06

Abstract
Background
Low efficacy of miltefosine in the treatment of visceral leishmaniasis was recently observed in Eastern Africa.
Objectives
To describe the pharmacokinetics and establish a pharmacokinetic/pharmacodynamic relationship for miltefosine in Eastern African patients with visceral leishmaniasis, using a time-to-event approach to model relapse of disease.
Methods
Miltefosine plasma concentrations from 95 patients (48 monotherapy versus 47 combination therapy) were included in the population pharmacokinetic model using non-linear mixed effects modelling. Subsequently a time-to-event model was developed to model the time of clinical relapse. Various summary pharmacokinetic parameters (various AUCs, Time > EC50, Time > EC90), normalized within each treatment arm to allow simultaneous analysis, were evaluated as relapse hazard-changing covariates.
Results
A two-compartment population model with first-order absorption fitted the miltefosine pharmacokinetic data adequately. Relative bioavailability was reduced (−74%, relative standard error 4.7%) during the first week of treatment of the monotherapy arm but only the first day of the shorter combination regimen. Time to the relapse of infection could be described using a constant baseline hazard (baseline 1.8 relapses/year, relative standard error 72.7%). Miltefosine Time > EC90 improved the model significantly when added in a maximum effect function on the baseline hazard (half maximal effect with Time > EC90 6.97 days for monotherapy).
Conclusions
Miltefosine drug exposure was found to be decreased in Eastern African patients with visceral leishmaniasis, due to a (transient) initial lower bioavailability. Relapse hazard was inversely linked to miltefosine exposure. Significantly lower miltefosine exposure was observed in children compared with adults, further urging the need for implementation of dose adaptations for children.



Plasma mitochondrial DNA levels are inversely associated with HIV-RNA levels and directly with CD4 counts: potential role as a biomarker of HIV replication

2017-08-31

Abstract
Objectives
To evaluate plasma mitochondrial DNA (mtDNA) levels among HIV-infected patients and its potential role as a biomarker of residual viral replication.
Methods
HIV-infected patients on follow-up at a reference hospital in north-west Spain were selected. DNA was isolated from plasma samples and mtDNA levels were assessed using a quantitative real-time PCR assay. HIV-RNA levels and CD4+ cell counts were evaluated in the same blood samples used for plasma mtDNA quantification. Epidemiological and clinical variables were included for the analysis.
Results
A total of 235 HIV-infected patients were included. Mean plasma mtDNA levels were 217 ± 656 copies/μL for naive (31.9%) and 364 ± 939 copies/μL for HIV-infected patients receiving ART and with suppressed viraemia (P =0.043). Among the latter, mean plasma mtDNA levels were 149 ± 440 copies/μL for those with low-level viraemia (LLV; HIV-RNA 20–200 copies/mL), 265 ± 723 copies/μL for those with detected-not-quantified (DNQ) viraemia (HIV-RNA <20 copies/mL) and 644 ± 1310 copies/μL for those with not-detected (ND) viraemia. Of note, a linear trend (P =0.006) was observed among virologically suppressed (LLV, DNQ and ND) patients. ND patients had higher mtDNA levels compared with LLV patients (P =0.057). Moreover, mtDNA levels were inversely associated with HIV-RNA levels (Spearman’s rho −0.191, P =0.003) and directly associated with CD4+ counts (Spearman’s rho 0.131, P =0.046).
Conclusions
Increased plasma mtDNA levels are associated with lower HIV-RNA levels and higher CD4+ cell counts. Among ART-suppressed patients, mtDNA levels were significantly higher in those with complete virological suppression (ND) than in those with LLV. These data suggest that plasma mtDNA levels might serve as a biomarker of residual HIV replication.



Comparison of the susceptibility of Plasmodium knowlesi and Plasmodium falciparum to antimalarial agents

2017-08-30

Abstract
Background
The simian malaria parasite Plasmodium knowlesi is now a well-recognized pathogen of humans in South-East Asia. Clinical infections appear adequately treated with existing drug regimens, but the evidence base for this practice remains weak. The availability of P. knowlesi cultures adapted to continuous propagation in human erythrocytes enables specific studies of in vitro susceptibility of the species to antimalarial agents, and could provide a surrogate system for testing investigational compounds against Plasmodium vivax and other non-Plasmodium falciparum infections that cannot currently be propagated in vitro.
Objectives
We sought to optimize protocols for in vitro susceptibility testing of P. knowlesi and to contrast outputs with those obtained for P. falciparum under comparable test conditions.
Methods
Growth monitoring of P. knowlesi in vitro was by DNA quantification using a SYBR Green fluorescent assay or by colorimetric detection of the lactate dehydrogenase enzyme. For comparison, P. falciparum was tested under conditions identical to those used for P. knowlesi.
Results
The SYBR Green I assay proved the most robust format over one (27 h) or two (54 h) P. knowlesi life cycles. Unexpectedly, P. knowlesi displays significantly greater susceptibility to the dihydrofolate reductase inhibitors pyrimethamine, cycloguanil and trimethoprim than does P. falciparum, but is less susceptible to the selective agents blasticidin and DSM1 used in parasite transfections. Inhibitors of dihydroorotate dehydrogenase also demonstrate lower activity against P. knowlesi.
Conclusions
The fluorescent assay system validated here identified species-specific P. knowlesi drug susceptibility profiles and can be used for testing investigational compounds for activity against non-P. falciparum malaria.



Quality of antibiotic prescribing of Swiss primary care physicians with high prescription rates: a nationwide survey

2017-08-24

Abstract
Objectives
To assess the quality of antibiotic prescribing of Swiss primary care physicians with high prescription rates.
Methods
In January 2015, we mailed a structured questionnaire to 2900 primary care physicians in Switzerland. They were included in a nationwide pragmatic randomized controlled trial on routine antibiotic prescription monitoring and feedback based on health insurance claims data. We asked them to record the diagnosis and antibiotic treatment for 44 consecutive patients with the most common conditions associated with antibiotic prescribing in primary care. We evaluated if the disease-specific antibiotic prescribing and the proportion of non-recommended antibiotics used, in particular quinolones, were within ‘acceptable ranges’ using adapted European Surveillance of Antimicrobial Consumption (ESAC) quality indicators.
Results
Two hundred and fifty physicians (8.6%) responded, providing 9961 patient records. Responders were similar to the entire physician population. Overall, antibiotics were prescribed to 32.1% of patients. For tonsillitis/pharyngitis, acute otitis media, acute rhinosinusitis and acute bronchitis the acceptable maximum of antibiotic prescriptions was exceeded by 24.4%, 49.6%, 27.4% and 11.5%, respectively. The proportion of non-recommended antibiotics was for all diagnoses above the recommended maximum of 20% (31.5%–88.7% across all conditions). Quinolones were prescribed to 37.2% of women with urinary tract infections, substantially exceeding the recommended maximum of 5%.
Conclusions
Antibiotic prescribing quality of Swiss primary care physicians with high prescription rates is low according to the indicators used, with substantial overtreatment of tonsillitis/pharyngitis, acute rhinosinusitis, acute otitis media and acute bronchitis. Routine nationwide and continuous monitoring of antibiotic use and specific interventions are warranted to improve prescribing in primary care.



HIV pretreatment drug resistance trends in three geographic areas of Mexico

2017-08-23

Abstract
Background
Pretreatment drug resistance (PDR) levels to NNRTI approaching 10% have recently been reported in Mexico. However, subnational differences may exist in PDR prevalence and transmission dynamics.
Objectives
We longitudinally assessed HIV PDR in three geographic areas of Mexico.
Patients and methods
HIV-infected, antiretroviral-naive individuals were recruited from 2008 to 2016, from the Central Metropolitan Zone (CMZ), Cancun and Tijuana (1194, 773 and 668 respectively). PDR was estimated using the Stanford HIVdb tool from plasma HIV pol sequences.
Results
A higher proportion of females, lower education and lower employment rate were observed in Tijuana, while a higher proportion of MSM was observed in the CMZ (P < 0.0001, all cases). For 2012–16, PDR was 13.4%, 8.9% and 11.2% in the CMZ, Tijuana and Cancun respectively. NNRTI PDR was highest in the three regions (8.7%, 4.8% and 8.1% respectively, P < 0.05); nevertheless, NNRTI PDR in Tijuana was lower than in the CMZ (P = 0.01). For 2008–16, we observed increasing efavirenz resistance trends in all regions (P < 0.05, all cases), reaching 11.8%, 6.1% and 8.3% respectively in 2016. Increasing efavirenz resistance was mostly associated with increasing K103N frequency (P = 0.007 CMZ, P = 0.03 Tijuana, not significant for Cancun).
Conclusions
Our study suggests different NNRTI PDR prevalence and transmission dynamics in three geographical areas of Mexico. Even when increasing trends in efavirenz resistance were observed in the three areas, our observations support that, in a large country such as Mexico, subnational surveillance and locally tailored interventions to address drug resistance may be a reasonable option.



A randomized controlled trial of probiotics for Clostridium difficile infection in adults (PICO)

2017-08-23

Abstract
Background
Clostridium difficile is the most common cause of hospital-acquired infections, responsible for >450000 infections annually in the USA. Probiotics provide a promising, well-tolerated adjunct therapy to standard C. difficile infection (CDI) treatment regimens, but there is a paucity of data regarding their effectiveness for the treatment of an initial CDI.
Objectives
We conducted a pilot randomized controlled trial of 33 participants from February 2013 to February 2015 to determine the feasibility and health outcomes of adjunct probiotic use in patients with an initial mild to moderate CDI.
Methods
The intervention was a 28 day, once-daily course of a four-strain oral probiotic capsule containing Lactobacillus acidophilus NCFM, Lactobacillus paracasei Lpc-37, Bifidobacterium lactis Bi-07 and B. lactis Bl-04. The control placebo was identical in taste and appearance. Registered at clinicaltrials.gov: trial registration number = NCT01680874.
Results
Probiotic adjunct therapy was associated with a significant improvement in diarrhoea outcomes. The primary duration of diarrhoea outcome (0.0 versus 1.0 days; P =0.039) and two exploratory outcomes, total diarrhoea days (3.5 versus 12.0 days; P =0.005) and rate of diarrhoea (0.1 versus 0.3 days of diarrhoea/stool diary days submitted; P =0.009), all decreased in participants with probiotic use compared with placebo. There was no significant difference in the rate of CDI recurrence or functional improvement over time between treatment groups.
Conclusions
Probiotics are a promising adjunct therapy for treatment of an initial CDI and should be further explored in a larger randomized controlled trial.



Safety and effectiveness of neuraminidase inhibitors for influenza treatment, prophylaxis, and outbreak control: a systematic review of systematic reviews and/or meta-analyses

2017-08-22

Abstract
Objectives
To review evidence from systematic reviews and/or meta-analyses (SR/MAs) regarding neuraminidase inhibitor (NI) safety and effectiveness.
Methods
We conducted an SR of SR/MAs of randomized control and/or observational studies. We searched eight electronic databases for SR/MAs that examined the effectiveness or safety of NIs administered for influenza (i.e. influenza-like illness or lab-confirmed) treatment or prophylaxis.
Results
We identified 27 (0.7%) eligible SR/MAs of 3723 articles reviewed. NI (n =2) or oseltamivir (n =1) versus no treatment were consistently associated with a decrease in mortality odds among the hospitalized, general population (OR range 0.2 − 0.8). Oseltamivir versus no treatment was associated with a decrease in hospitalization and pneumonia risk/odds in 2/4 SR/MAs. Oseltamivir (n =4) and zanamivir (n =3) were consistently associated with a 0.5 − 1 day decrease in symptom duration. Oseltamivir (n =4) or zanamivir (n =4) versus no prophylaxis were consistently associated with a decrease in the odds/risk of symptomatic secondary transmission (OR/RR range 0.1 − 0.5). Oseltamivir versus no treatment was consistently associated with a 1.5- to 2.5-fold increase in the odds/risk of nausea (n =4) and vomiting (n =5).
Conclusions
NI treatment is likely to be effective at reducing mortality among hospitalized patients, and symptom duration by up to 1 day in the general population. Oseltamivir or zanamivir prophylaxis are likely to be effective at reducing secondary symptomatic influenza transmission. Increased nausea and vomiting are likely associated with oseltamivir use. We recommend that decisions regarding NI use are made in consideration of potential adverse events, particularly for the general population at low risk of complications. Among hospitalized patients, NI administration seems warranted to reduce mortality risk.



M184I/V substitutions and E138K/M184I/V double substitutions in HIV reverse transcriptase do not significantly affect the antiviral activity of EFdA

2017-08-22

Abstract
Background
4′-Ethynyl-2-fluoro-2′-deoxyadenosine (EFdA) is a potent nucleoside analogue inhibitor of HIV that has an unusually long half-life. Cell culture selections with either EFdA or lamivudine using both subtype B and non-B clinical isolates selected the M184I/V substitutions in reverse transcriptase (RT). Unlike lamivudine, however, EFdA retained significant activity against viruses containing the M184I/V substitutions. In other clinical trials that evaluated rilpivirine together with emtricitabine in first-line therapy, the emergence of both the M184I/V and E138K mutations in RT was demonstrated. Moreover, the M184I/V and E138K substitutions were shown to be compensatory for each other with regard to both efficiency of RT activity and viral replicative capacity. This creates concern that E138K might emerge as a compensatory mutation for M184I/V in the aftermath of the use of EFdA.
Objectives
We wished to determine whether the E138K mutation in HIV RT together with M184I/V would compromise the activity of EFdA.
Methods
Recombinant viruses containing the M184I/V and/or E138K substitutions were generated by site-directed mutagenesis and evaluated in tissue culture for susceptibility to various nucleoside compounds, including EFdA.
Results
Susceptibility to EFdA was retained in M184I/V viruses that also contained the E138K substitution. Moreover, the E138K substitution was not generated in these studies under selection pressure with EFdA.
Conclusions
These findings help to alleviate concern that EFdA may not be active against viruses that contain both the M184I/V and E138K substitutions in RT.



Atazanavir intracellular concentrations remain stable during pregnancy in HIV-infected patients

2017-08-22

Abstract
Background
Atazanavir (300 mg) boosted by ritonavir (100 mg) is the preferred third drug in pregnancy. However, there is still discordance on atazanavir dose increase during the third trimester.
Objectives
To evaluate plasma and intracellular atazanavir and ritonavir concentrations in HIV-infected women during pregnancy and after delivery.
Methods
This was an observational study. HIV-infected pregnant patients treated with atazanavir/ritonavir plus either tenofovir/emtricitabine or abacavir/lamivudine had been prospectively enrolled after having signed a written informed consent form. Plasma and intracellular atazanavir and ritonavir Ctrough (24 ± 3 h after drug intake) were measured at each visit during the first, second and third trimesters and post-partum using validated HPLC-MS and HPLC-photodiode array methods (with direct evaluation of cellular volume). Data are described as median (IQR) and compared through non-parametric tests.
Results
Twenty-five patients were enrolled; at baseline, the median age was 32 years (27–35). All patients had plasma HIV RNA <50 copies/mL; the median CD4+ count was 736 cells/mm3 (542–779). Atazanavir plasma concentrations were 441 ng/mL (261–1557), 710 ng/mL (338–1085), 556 ng/mL (334–1022) and 837 ng/mL (608–1757) during the first, second and third trimesters and post-partum, respectively; intracellular concentrations were 743 ng/mL (610–1928), 808 ng/mL (569–1620), 756 ng/mL (384–1074) and 706 ng/mL (467–2688), respectively. Atazanavir intracellular/plasma ratios were 1.32 (0.98–2.77), 1.34 (1.13–1.88), 1.38 (0.61–2.63) and 1.07 (0.56–2.69), respectively. Atazanavir intracellular concentrations and intracellular/plasma ratios showed non-significant changes over time (P > 0.05).
Conclusions
This is the first demonstration that intracellular atazanavir exposure remains unchanged during pregnancy supporting the standard 300/100 mg atazanavir/ritonavir dosing throughout pregnancy.



Synergistic antibiotic activity against planktonic and biofilm-embedded Streptococcus agalactiae , Streptococcus pyogenes and Streptococcus oralis

2017-08-21

Abstract
Objectives
To determine the antimicrobial activity against streptococcal biofilm in species mostly isolated from implant-associated infections and examine the effect of enzyme treatment of biofilm on the antimicrobial activity of different antibiotics.
Methods
The activities of fosfomycin, rifampicin, benzylpenicillin, daptomycin, gentamicin, levofloxacin, proteinase K and their combinations on planktonic and/or biofilm-embedded standard laboratory strains of Streptococcus agalactiae, Streptococcus pyogenes and Streptococcus oralis were investigated in vitro by standard methods and isothermal microcalorimetry.
Results
MIC values obtained for the tested antimicrobials against planktonic bacteria ranged from 0.016 to 128 mg/L for the three species tested. Higher antibiotic concentrations were usually required to reduce biofilm in comparison with planktonic bacteria, with the exception of gentamicin, for which similar concentrations (4–16 mg/L) exerted an effect on both planktonic and biofilm cells. A synergistic effect against the streptococcal biofilm of the three species was observed when gentamicin was combined with benzylpenicillin or with rifampicin. Moreover, antibiotic concentrations comparable to the MIC observed against planktonic cells induced a strong reduction of viable bacteria in proteinase K pre-treated biofilm.
Conclusions
This study shows that the combination of gentamicin with either benzylpenicillin or rifampicin exerts a synergistic effect against biofilms produced by the tested streptococci strains in vitro. Our results also suggest that coupling a dispersal agent with conventional antibiotics may facilitate their access to the bacteria within the biofilm. In vivo and clinical studies are needed in order to confirm whether such a strategy may be effective in the treatment of implant-associated infections caused by streptococci.



Sustained impact of a rapid microarray-based assay with antimicrobial stewardship interventions on optimizing therapy in patients with Gram-positive bacteraemia

2017-08-21

Abstract
Objectives
To compare antibiotic optimization and outcomes of patients before implementation of the Verigene Gram-Positive Blood Culture (Verigene BC-GP) nucleic acid microarray assay to after implementation with antimicrobial stewardship (AS) interventions and after discontinuation of AS interventions.
Methods
A retrospective pre–post–post quasi-experimental study was conducted to compare the three periods. AS interventions consisted of real-time guidance to clinicians on antibiotic selection. The primary outcome was median time from Gram stain to optimal therapy. Secondary outcomes included median time to effective therapy, median duration of therapy for contaminant organisms, median length of stay after blood cultures were collected, and all-cause in-hospital mortality.
Results
Out of a total of 923 patients, 390 (125 baseline, 134 intervention, 131 post-intervention) who were not on optimal therapy at the time of Gram stain or had contaminated blood cultures were assessed. Compared with baseline, only the median time to optimal therapy for MSSA bacteraemia was reduced in both the intervention and post-intervention periods (17 versus 17 versus 50 h; P <0.001), respectively. In an analysis adjusted for baseline differences among the groups using quantile regression models, use of the Verigene BC-GP assay in both periods significantly reduced time to optimal therapy by 14–22 h in patients who would achieve optimal therapy at ≥ 26 h without the assay. There were no differences in in-hospital mortality or hospital length of stay between study periods.
Conclusions
A real-time AS intervention implemented alongside introduction of the Verigene BC-GP assay led to improvements in antibiotic therapy for patients with bacteraemia due to Gram-positive cocci, even after the AS intervention was discontinued.



Structural modification of LPS in colistin-resistant, KPC-producing Klebsiella pneumoniae

2017-08-18

Abstract
Background
Colistin resistance in Klebsiella pneumoniae typically involves inactivation or mutations of chromosomal genes mgrB, pmrAB or phoPQ, but data regarding consequent modifications of LPS are limited.
Objectives
To examine the sequences of chromosomal loci implicated in colistin resistance and the respective LPS-derived lipid A profiles using 11 pairs of colistin-susceptible and -resistant KPC-producing K. pneumoniae clinical strains.
Methods
The strains were subjected to high-throughput sequencing with Illumina HiSeq. The mgrB gene was amplified by PCR and sequenced. Lipid profiles were determined using MALDI-TOF MS.
Results
All patients were treated with colistimethate prior to the isolation of colistin-resistant strains (MIC >2 mg/L). Seven of 11 colistin-resistant strains had deletion or insertional inactivation of mgrB. Three strains, including one with an mgrB deletion, had non-synonymous pmrB mutations associated with colistin resistance. When analysed by MALDI-TOF MS, all colistin-resistant strains generated mass spectra containing ions at m/z 1955 and 1971, consistent with addition of 4-amino-4-deoxy-l-arabinose (Ara4N) to lipid A, whereas only one of the susceptible strains displayed this lipid A phenotype.
Conclusions
The pathway to colistin resistance in K. pneumoniae primarily involves lipid A modification with Ara4N in clinical settings.



Fitness cost constrains the spectrum of marR mutations in ciprofloxacin-resistant Escherichia coli

2017-08-17

Abstract
Objectives
To determine whether the spectrum of mutations in marR in ciprofloxacin-resistant clinical isolates of Escherichia coli shows evidence of selection bias, either to reduce fitness costs, or to increase drug resistance. MarR is a repressor protein that regulates, via MarA, expression of the Mar regulon, including the multidrug efflux pump AcrAB-TolC.
Methods
Isogenic strains carrying 36 different marR alleles identified in resistant clinical isolates, or selected for resistance in vitro, were constructed. Drug susceptibility and relative fitness in growth competition assays were measured for all strains. The expression level of marA, and of various efflux pump components, as a function of specific mutations in marR, was measured by qPCR.
Results
The spectrum of genetic alterations in marR in clinical isolates is strongly biased against inactivating mutations. In general, the alleles found in clinical isolates conferred a lower level of resistance and imposed a lower growth fitness cost than mutations selected in vitro. The level of expression of MarA correlated well with the MIC of ciprofloxacin. This supports the functional connection between mutations in marR and reduced susceptibility to ciprofloxacin.
Conclusions
Mutations in marR selected in ciprofloxacin-resistant clinical isolates are strongly biased against inactivating mutations. Selection favours mutant alleles that have the lowest fitness costs, even though these cause only modest reductions in drug susceptibility. This suggests that selection for high relative fitness is more important than selection for increased resistance in determining which alleles of marR will be selected in resistant clinical isolates.



Can a pharmacokinetic/pharmacodynamic (PKPD) model be predictive across bacterial densities and strains? External evaluation of a PKPD model describing longitudinal in vitro data

2017-08-17

Abstract
Background
Pharmacokinetic/pharmacodynamic (PKPD) models developed based on data from in vitro time–kill experiments have been suggested to contribute to more efficient drug development programmes and better dosing strategies for antibiotics. However, for satisfactory predictions such models would have to show good extrapolation properties.
Objectives
To evaluate if a previously described mechanism-based PKPD model was able also to predict drug efficacy for higher bacterial densities and across bacterial strains.
Methods
A PKPD model describing the efficacy of ciprofloxacin on Escherichia coli was evaluated. The predictive performance of the model was evaluated across several experimental conditions with respect to: (i) bacterial start inoculum ranging from the standard of ∼106 cfu/mL up to late stationary-phase cultures; and (ii) efficacy for seven additional strains (three laboratory and four clinical strains), not included during the model development process, based only on information regarding their MIC. Model predictions were performed according to the intended experimental protocol and later compared with observed bacterial counts.
Results
The mechanism-based PKPD model structure developed based on data from standard start inoculum experiments was able to accurately describe the inoculum effect. The model successfully predicted the time course of drug efficacy for additional laboratory and clinical strains based on only the MIC values. The model structure was further developed to better describe the stationary phase data.
Conclusions
This study supports the use of mechanism-based PKPD models based on preclinical data for predictions of untested scenarios.



Biological evaluation of diphenyleneiodonium chloride (DPIC) as a potential drug candidate for treatment of non-tuberculous mycobacterial infections

2017-08-17

Abstract
Background
Novel drug discovery against non-tuberculous mycobacteria is beset with a large number of challenges including the existence of myriad innate drug resistance mechanisms as well as a lack of suitable animal models, which hinders effective translation. In order to identify molecules acting via novel mechanisms of action, we screened the Library of Pharmacologically Active Compounds against non-tuberculous mycobacteria to identify such compounds.
Methods
Whole-cell growth inhibition assays were used to screen and identify novel inhibitors. The hit compounds were tested for cytotoxicity against Vero cells to determine the selectivity index, and time–kill kinetics were determined against Mycobacterium fortuitum. The compound’s ability to synergize with amikacin, ceftriaxone, ceftazidime and meropenem was determined using fractional inhibitory concentration indexes followed by its ability to decimate mycobacterial infections ex vivo. Finally, the in vivo potential was determined in a neutropenic murine model mimicking mycobacterial infection.
Results
We have identified diphenyleneiodonium chloride (DPIC), an NADPH/NADH oxidase inhibitor, as possessing potent antimicrobial activity against non-tuberculous mycobacteria. DPIC exhibited concentration-dependent bactericidal activity against M. fortuitum and synergized with amikacin, ceftriaxone, ceftazidime and meropenem. When tested in a murine neutropenic M. fortuitum infection model, DPIC caused a significant reduction in bacterial load in kidney and spleen. The reduction in bacterial count is comparable to amikacin at a 100-fold lower concentration.
Conclusions
DPIC exhibits all properties to be repositioned as a novel anti-mycobacterial therapy and possesses a potentially new mechanism of action. Thus, it can be projected as a potential new therapeutic against ever-increasing non-tuberculous mycobacterial infections.



Risk of HIV transmission during combined ART initiation for HIV-infected persons with severe immunosuppression

2017-08-14

Abstract
Background
Individuals presenting for care with severe immunosuppression typically have high plasma HIV viral load (pVL) and may transmit HIV before and after initiation of combination antiretroviral therapies (cART).
Patients and methods
Using risk equations and data collected in the IMEA 040 DATA trial on sexual behaviour and pVL level of 84 HIV-infected patients (23 women), we estimated monthly rates of HIV transmission for each virologically unsuppressed participant (pVL >50 copies/mL) who reported sex with HIV-negative or unknown serostatus (HNUS) partners at cART initiation, 24 weeks (W24) and W48 after; rates were considered negligible for other participants.
Results
At cART initiation, median pVL was 5.4 log10 copies/mL. The percentage of virologically unsuppressed patients decreased, from 100% at cART initiation to 27% (95% CI 16%–43%) for heterosexuals and 8% (95% CI 2%–22%) for MSM at W48 (P <0.001). The percentage of patients reporting sex with HNUS partners increased between cART initiation and W48, from 23% (95% CI 10%–42%) to 42% (95% CI 25%–61%) for heterosexuals (P =0.042) and from 41% (95% CI 21%–64%) to 73% (95% CI 52%–88%) for MSM (P =0.004). Median monthly HIV transmission rates were 0.0540 (IQR 0.0339–0.0742) for MSM and 0.0018 (IQR 0.0014–0.0191) for heterosexuals at cART initiation, and were reduced by 95% (95% CI 87%–100%) for heterosexuals and 98% (95% CI 95%–100%) for MSM as early as W24.
Conclusions
Risk of onward transmission for severely immunosuppressed individuals is high before and within the first weeks of cART, and persists, at a substantially reduced level, beyond 24 weeks of cART for some individuals. Earlier cART and protecting HIV-negative partners until full viral suppression is achieved could reduce HIV transmission.



Susceptibility of MDR Pseudomonas aeruginosa to ceftolozane/tazobactam and comparison of different susceptibility testing methods

2017-08-11

Abstract
Background
Infections caused by MDR Pseudomonas aeruginosa are on the rise, particularly in critically ill patients. Therefore, there is a need to evaluate new antimicrobial regimens. The objectives of this study were to investigate the ceftolozane/tazobactam resistance rates of MDR and XDR P. aeruginosa, the underlying resistance genes, the clonal structure and different antimicrobial susceptibility testing (AST) methods regarding their accuracy for ceftolozane/tazobactam testing.
Methods
In total, 112 MDR and XDR P. aeruginosa (from infection and colonization) from one German tertiary care hospital were included (2013–16). AST was done using broth microdilution (BMD), gradient diffusion test strips and disc diffusion. Resistance genes were screened by PCR. A randomly selected subset of 77 isolates was subjected to WGS to assess the clonal structure.
Results
In total, 38 isolates (33.9%) were resistant to ceftolozane/tazobactam according to the BMD reference method. Resistance was significantly lower in MDR P. aeruginosa (4.8%) compared with XDR P. aeruginosa (50%, P <0.0001). The underlying mechanism in carbapenemase-positive ceftolozane/tazobactam-resistant isolates (n =38) was blaIMP (n =25), blaVIM (n =4) and blaGES (n =1). The resistance mechanism of the remaining eight ceftolozane/tazobactam-resistant isolates remained unclear. Although our strain collection was diverse, resistance to ceftolozane/tazobactam was almost exclusively associated with MLST ST235. The disc diffusion method was accurate for ceftolozane/tazobactam AST (no false-susceptible results, categorical agreement = 92.9%).
Conclusions
Ceftolozane/tazobactam resistance was low in MDR P. aeruginosa, but higher in XDR P. aeruginosa. The disc diffusion method showed an acceptable accuracy for ceftolozane/tazobactam AST.



Shigella species epidemiology and antimicrobial susceptibility: the implications of emerging azithromycin resistance for guiding treatment, guidelines and breakpoints

2017-08-10

Abstract
Objectives
To examine antimicrobial susceptibility patterns and predictors of resistance among Shigella isolates in New South Wales (NSW), Australia during 2013–14 with emphasis on azithromycin.
Methods
Cross-sectional analysis of all shigellosis cases (160) notified to public health authorities in NSW, Australia was performed.
Results
Among 160 Shigella isolates tested, 139 (86.9%) were susceptible to azithromycin, 104 (65.0%) to ciprofloxacin and 38 (23.7%) to co-trimoxazole. Ciprofloxacin resistance was 1.9 times more common in infections acquired in Australia compared with those acquired overseas, while azithromycin resistance was 8.5 times more common in males.
Conclusions
We recommend ongoing reconsideration of guidelines for the treatment of shigellosis based on emerging resistance patterns. First-line therapy may need to be reconsidered based on local resistance rates due to common resistance to co-trimoxazole and ciprofloxacin. We recommend culture and susceptibility testing for suspected and proven shigellosis. Azithromycin susceptibility breakpoints for Shigella species may need to be species specific.



Detection of azole-susceptible and azole-resistant Aspergillus coinfection by cyp51A PCR amplicon melting curve analysis

2017-08-09

Abstract
Background
The AsperGenius® assay is a multiplex real-time PCR test that allows the simultaneous detection of Aspergillus species and identification of the most common mutations in the Aspergillus fumigatus cyp51A gene conferring resistance (TR34/L98H and TR46/T289A/Y121F) by using melting curve analysis. Mixed infections with azole-resistant and susceptible A. fumigatus have rarely been described.
Methods
The AsperGenius® multiplex real-time PCR assay (PathoNostics, Maastricht, the Netherlands) was used on bronchoalveolar lavage (BAL) samples of 91 consecutive patients with a suspected invasive Aspergillus infection at the Erasmus MC University Medical Center, Rotterdam.
Results
In three cases the AsperGenius® assay indicated the simultaneous presence of WT and mutant genes (two patients with TR34/L98H mutation and one patient with TR46/T289A/Y121F mutation) and therefore mixed infections with azole-susceptible and -resistant isolates. In one of the three cases, the mixed infection was confirmed by phenotypic antifungal testing of multiple A. fumigatus colonies.
Conclusions
The use of a dedicated A. fumigatus cyp51A resistance PCR allowed the detection of mixed infections with azole-resistant and -susceptible Aspergillus strains. These mixed infections may remain undiagnosed with conventional phenotypic susceptibility testing.



Rapid detection of ESBL, carbapenemases, MRSA and other important resistance phenotypes within 6–8 h by automated disc diffusion antibiotic susceptibility testing

2017-08-09

Abstract
Background
In principle, automated systems allow rapid reading of disc diffusion AST (rAST) within 6–8 h.
Objectives
This study analysed whether rAST can discriminate resistance phenotypes such as ESBL, carbapenemases and MRSA/methicillin-resistant Staphylococcus epidermidis from WT populations. We describe species–drug combinations that may require clinical breakpoint adaptions for early reading due to zone diameter changes during the incubation period.
Methods
In total, 1852 clinical strains [Escherichia coli (n =475), Klebsiella pneumoniae (n =375), Enterobacter cloacae (n =301), Staphylococcus aureus (n =407) and S. epidermidis (n =294)] were included in this study comprising WT populations and important resistance phenotypes, e.g. ESBL, carbapenemases and MRSA. We assessed (i) separation of resistance phenotypes and WT populations after 6, 8 and 12 h as compared with the 18 h standard, and (ii) diameter changes of WT populations and associated putative epidemiological cut-offs during the incubation period. Disc diffusion plates were automatically streaked, incubated and imaged using the WASPLabTM system.
Results and conclusions
We demonstrated that important resistance phenotypes could reliably be separated from WT populations at early reading times for the most prevalent bacterial pathogens encountered in the clinical laboratory. Current AST expert rules and algorithms for identification of resistance mechanisms can readily be applied for rAST, e.g. EUCAST recommended rules for detection of ESBL, AmpC, carbapenemases and MRSA/methicillin-resistant S. epidermidis. However, several species–drug combinations may require clinical breakpoint adaptations when using rAST as the diameter, and hence the epidemiological cut-off, changes during the incubation period.



Covert dissemination of carbapenemase-producing Klebsiella pneumoniae (KPC) in a successfully controlled outbreak: long- and short-read whole-genome sequencing demonstrate multiple genetic modes of transmission

2017-08-07

Abstract
Background
Carbapenemase-producing Enterobacteriaceae (CPE), including KPC-producing Klebsiella pneumoniae (KPC-Kpn), are an increasing threat to patient safety.
Objectives
To use WGS to investigate the extent and complexity of carbapenemase gene dissemination in a controlled KPC outbreak.
Materials and methods
Enterobacteriaceae with reduced ertapenem susceptibility recovered from rectal screening swabs/clinical samples, during a 3 month KPC outbreak (2013–14), were investigated for carbapenemase production, antimicrobial susceptibility, variable-number-tandem-repeat profile and WGS [short-read (Illumina), long-read (MinION)]. Short-read sequences were used for MLST and plasmid/Tn4401 fingerprinting, and long-read sequence assemblies for plasmid identification. Phylogenetic analysis used IQTree followed by ClonalFrameML, and outbreak transmission dynamics were inferred using SCOTTI.
Results
Twenty patients harboured KPC-positive isolates (6 infected, 14 colonized), and 23 distinct KPC-producing Enterobacteriaceae were identified. Four distinct KPC plasmids were characterized but of 20 KPC-Kpn (from six STs), 17 isolates shared a single pKpQIL-D2 KPC plasmid. All isolates had an identical transposon (Tn4401a), except one KPC-Kpn (ST661) with a single nucleotide variant. A sporadic case of KPC-Kpn (ST491) with Tn4401a-carrying pKpQIL-D2 plasmid was identified 10 months before the outbreak. This plasmid was later seen in two other species and other KPC-Kpn (ST14,ST661) including clonal spread of KPC-Kpn (ST661) from a symptomatic case to nine ward contacts.
Conclusions
WGS of outbreak KPC isolates demonstrated blaKPC dissemination via horizontal transposition (Tn4401a), plasmid spread (pKpQIL-D2) and clonal spread (K. pneumoniae ST661). Despite rapid outbreak control, considerable dissemination of blaKPC still occurred among K. pneumoniae and other Enterobacteriaceae, emphasizing its high transmission potential and the need for enhanced control efforts.



Comparative evaluation of VITEK ® 2 and three commercial gradient strip assays for daptomycin susceptibility testing of Staphylococcus aureus

2017-08-07

Abstract
Objectives
MRSA remains a major cause of severe nosocomial infections and the increased use of vancomycin and daptomycin for MRSA treatment over the last decade has led to the isolation of MRSA strains with decreased daptomycin susceptibility. In addition, a growing number of MSSA isolates with reduced susceptibility to daptomycin have been described lately. Surveillance of the emergence of such a daptomycin-non-susceptible MSSA population requires prompt and reliable daptomycin susceptibility testing. Therefore, this work aimed to evaluate the ability of commonly used methods to detect daptomycin resistance in clinical microbiological laboratories.
Methods
We used commercially available manual and automated test systems, including VITEK® 2 and three gradient strip assays, in comparison with broth microdilution, to detect daptomycin resistance in a representative Staphylococcus aureus strain collection.
Results
We found high inter-assay concordance as well as congruence with the reference method. This is demonstrated by essential agreement between commercial test systems and reference broth microdilution ranging from 98.1% to 100% and by categorical agreement from 98.2% to 99.1%. Thus, all systems used were able to detect daptomycin non-susceptibility in MRSA and MSSA isolates.
Conclusions
Our data indicate that routine laboratories are at limited risk of overlooking further daptomycin resistance development, as long as commercially available test systems are used according to the manufacturer's recommendations. However, laboratories must be aware of an increasing number of daptomycin-non-susceptible MSSA isolates, including those exhibiting elevated MICs of glycopeptides.



A current perspective on antimicrobial resistance in Southeast Asia

2017-08-07

Abstract
Southeast Asia, a vibrant region that has recently undergone unprecedented economic development, is regarded as a global hotspot for the emergence and spread of antimicrobial resistance (AMR). Understanding AMR in Southeast Asia is crucial for assessing how to control AMR on an international scale. Here we (i) describe the current AMR situation in Southeast Asia, (ii) explore the mechanisms that make Southeast Asia a focal region for the emergence of AMR, and (iii) propose ways in which Southeast Asia could contribute to a global solution.



Impact of carbapenem restriction on the antimicrobial susceptibility pattern of Pseudomonas aeruginosa isolates in the ICU

2017-08-04

Abstract
Background
Rates of carbapenem-resistant Pseudomonas aeruginosa are increasing. Aggressive prevention strategies, including instituting antimicrobial stewardship programmes, are essential for combating antimicrobial resistance.
Objectives
We conducted this study to compare the antimicrobial susceptibility pattern of P. aeruginosa before and after carbapenem restriction.
Methods
We conducted a two-phase retrospective study in an adult ICU. The first phase was from May until July 2016 (before carbapenem restriction), whereas the second phase was from September until November 2016 (while implementing carbapenem restriction). The antimicrobial susceptibility pattern of P. aeruginosa was reviewed in August and December 2016. The measure of carbapenem-resistant P. aeruginosa was the proportion of resistant isolates (percentage resistant). The measure of antibacterial consumption in the study phases was DDDs/1000 patient days.
Results
The overall carbapenem consumption decreased significantly in the second phase, from 28.44 to 11.67 DDDs/1000 patient days (P = 0.012). The resistance of P. aeruginosa to imipenem and meropenem decreased significantly from 76.0% to 38.5% (P = 0.019) and from 74.1% to 30.0% (P = 0.012), respectively. Susceptibility of P. aeruginosa to other antibacterials was not affected by carbapenem restriction.
Conclusions
These data suggest that restricting carbapenems, even for a short duration, may be an effective strategy for managing the problem of carbapenem resistance in P. aeruginosa.



Rates of virological suppression and drug resistance in adult HIV-1-positive patients attending primary healthcare facilities in KwaZulu-Natal, South Africa

2017-08-03

Abstract
Background
KwaZulu-Natal (KZN) Province in South Africa has the highest HIV disease burden in the country, with an estimated population prevalence of 24.7%. A pilot sentinel surveillance project was undertaken in KZN to classify the proportion of adult patients failing first-line ART and to describe the patterns of drug resistance mutations (DRMs) in patients with virological failure (VF).
Methods
Cross-sectional surveillance of acquired HIV drug resistance was conducted in 15 sentinel ART clinics between August and November 2013. Two population groups were surveyed: on ART for 12–15 months (Cohort A) or 24–36 months (Cohort B). Plasma specimens with viral load ≥1000 copies/mL were defined as VF and genotyped for DRMs.
Results
A total of 1299 adults were included in the analysis. The prevalence of VF was 4.0% (95% CI 1.8–8.8) among 540 adults in Cohort A and 7.7% (95% CI 4.4–13.0) of 759 adults in Cohort B. Treatment with efavirenz was more likely to suppress viral load in Cohort A (P =0.005). Independent predictors of VF for Cohort B included male gender, advanced WHO stage at ART initiation and treatment with stavudine or zidovudine compared with tenofovir. DRMs were detected in 89% of 123 specimens with VF, including M184I/V, K103N/S, K65N/R, V106A/M and Y181C.
Conclusions
VF in adults in KZN was <8% up to 3 years post-ART initiation but was associated with a high frequency of DRMs. These data identify key groups for intensified adherence counselling and highlight the need to optimize first-line regimens to maintain viral suppression.



Cryptic silver resistance is prevalent and readily activated in certain Gram-negative pathogens

2017-08-02

Abstract
Objectives
To assess the prevalence of cryptic silver (Ag+) resistance amongst clinical isolates of Gram-negative bacteria, and to examine how overt Ag+ resistance becomes activated in such strains.
Methods
Established methods were used to determine the susceptibility of 444 recent clinical isolates to Ag+, and to evaluate the potential for overt Ag+ resistance to emerge in susceptible isolates by spontaneous mutation. The genetic basis for Ag+ resistance was investigated using PCR amplification and DNA sequencing.
Results
None of the isolates tested displayed overt Ag+ resistance. However, upon silver challenge, high-level Ag+ resistance (silver nitrate MIC >128 mg/L) was selected at high frequency (10−7 to 10−8) in 76% of isolates of Enterobacter spp., ∼58% of isolates of Klebsiella spp. and ∼0.7% of isolates of Escherichia coli. All strains in which Ag+ resistance could be selected harboured the sil operon, with resistance apparently resulting from activation of this system as a consequence of single missense mutations in silS. By contrast, Ag+ resistance was not selected in isolates lacking sil, which included all tested representatives of Pseudomonas aeruginosa, Acinetobacter spp., Citrobacter spp. and Proteus spp.
Conclusions
Whilst overt Ag+ resistance in Gram-negative pathogens is uncommon, cryptic Ag+ resistance pertaining to the sil operon is prevalent and readily activated in particular genera (Enterobacter and Klebsiella).



The economic evaluation of an antibiotic checklist as antimicrobial stewardship intervention

2017-08-01

Abstract
Objectives
An antibiotic checklist was introduced in nine Dutch hospitals to improve appropriate antibiotic use. We estimated the cost-effectiveness of checklist use.
Methods
We compared 853 patients treated with an antibiotic before checklist introduction (usual care group) with 1207 patients treated after introduction (checklist group). We calculated the change of costs between these groups per unit effect [incremental cost-effectiveness ratio (ICER)]: per extra patient receiving appropriate treatment; and per day reduction in length of hospital stay (LOS). We also calculated the benefit-to-cost ratio per day reduction in LOS. Finally, we estimated the number of checklists after which the expected benefits would compensate for costs in one hospital.
Results
The cost of checklist use per patient was €10.10. Of the usual care patients, 48.8% received appropriate antibiotic treatment compared with 67.5% of the checklist patients (+18.7%). The ICER was €54.01 (1010/18.7) per extra patient with appropriate treatment. In a model calculation the expected effect of appropriate antibiotic use was a reduction in LOS of 1.05 days, which was extrapolated to a reduction of 19.64 hospital days per 100 patients. The ICER was €51.43 (1010/19.64) per day reduction in LOS. The estimated benefit of a 1 day reduction was €611. The benefit-to-cost ratio was 11.9 (611/51.43) per day reduction in LOS, indicating a cost saving of €12 for every euro spent on checklist use. The benefits would compensate for costs after use of 11 checklists.
Conclusions
Efforts for further implementation of the antibiotic checklist can be justified by potential economic benefits.



Testing the mutant selection window hypothesis with Staphylococcus aureus exposed to linezolid in an in vitro dynamic model

2017-07-31

Abstract
Objectives
To test the mutant selection window (MSW) hypothesis applied to linezolid-exposed Staphylococcus aureus and to delineate the concentration–resistance relationship, a mixed inoculum of linezolid-susceptible S. aureus cells and linezolid-resistant mutants (RMs) was exposed to linezolid multiple dosing.
Methods
Three S. aureus strains (MIC of linezolid 2 mg/L), S. aureus 479, S. aureus 688 and S. aureus ATCC 700699, and their RMs (MIC 8 mg/L) selected by passaging on antibiotic-containing media were used in the study. RMs of S. aureus 479 and S. aureus ATCC 700699 contained a G2576T replacement (Escherichia coli numbering) in one of the copies of the 23S rRNA gene, which had been reported in clinically isolated mutants. Five-day treatments with twice-daily linezolid were simulated over a 32-fold range of the 24 h AUC (AUC24) to the MIC ratio.
Results
A pronounced enrichment of mutants resistant to 2×, 4× and 8× MIC was observed at AUC24/MIC ratios of 30 and 60 when linezolid concentrations were within the MSW for more than half of the dosing interval for each strain. The number of viable mutant cells decreased significantly at the simulated AUC24/MIC ratio of 120, while the AUC24/MIC ratio of 240 completely prevented mutant enrichment in vitro. Bell-shaped AUBCM–AUC24/MIC and AUBCM–AUC24/MPC relationships (r2 0.91 and 0.79, respectively) were strain independent.
Conclusions
The bell-shaped pattern of AUC24/MIC and AUC24/MPC relationships with S. aureus resistance to linezolid is consistent with the MSW hypothesis. ‘Antimutant’ AUC24/MIC ratios were predicted based on the AUC24/MIC relationship with AUBCM.



ZAAPS Program results for 2015: an activity and spectrum analysis of linezolid using clinical isolates from medical centres in 32 countries

2017-07-25

Abstract
Objectives
To report the linezolid in vitro activity obtained during the 2015 ZAAPS Program.
Methods
In total, 7587 organisms causing documented infections were consecutively collected in 65 centres in 32 ex-USA countries. Broth microdilution susceptibility testing was performed. Isolates displaying linezolid MIC results of ≥ 4 mg/L were molecularly characterized.
Results
Linezolid inhibited >99.9% of Staphylococcus aureus at ≤ 2 mg/L, with MIC50 results of 1 mg/L, regardless of methicillin resistance. A similar linezolid MIC50 result (0.5 mg/L) was observed for CoNS, with the vast majority of isolates (99.7%) also inhibited at ≤ 2 mg/L. Three CoNS (linezolid MIC, 16–64 mg/L) from Italy were found to contain alterations in the 23S rRNA and/or L3/L4 ribosomal proteins. One isolate also harboured cfr. Linezolid exhibited consistent modal MIC and MIC50 results (1 mg/L) for enterococci regardless of species or vancomycin resistance. One Enterococcus faecalis (linezolid MIC, 8 mg/L) from Galway, Ireland, carried optrA. One Enterococcus faecium (linezolid MIC, 16 mg/L) from Italy contained a G2576T mutation in the 23S rRNA. All Streptococcus pneumoniae, viridans group streptococci and β-haemolytic streptococci were inhibited by linezolid at ≤ 2, ≤ 2 and ≤ 1 mg/L, respectively, with equivalent MIC90 results (1 mg/L for all groups).
Conclusions
These results document the continued long-term and stable in vitro potency of linezolid and a limited number of isolates with decreased susceptibility to linezolid (MIC, ≥4 mg/L). The latter isolates showed primarily mutations in the 23S rRNA gene and/or L3/L4 proteins, with plasmid-mediated resistance (cfr and optrA) also present, albeit at a low prevalence.



National disparities in the relationship between antimicrobial resistance and antimicrobial consumption in Europe: an observational study in 29 countries

2017-07-25

Abstract
Background
Antimicrobial resistance in invasive infections is driven mainly by human antimicrobial consumption. Limited cross-national comparative evidence exists about variation in antimicrobial consumption and effect on resistance.
Methods
We examined the relationship between national community antimicrobial consumption rates (2013) and national hospital antimicrobial resistance rates (2014) across 29 countries in the European Economic Area (EEA). Consumption rates were obtained from the European Surveillance of Antimicrobial Consumption Network (ESAC-Net). Resistance data were obtained from the European Antimicrobial Resistance Surveillance Network (EARS-Net), based on 196480 invasive isolates in 2014.
Results
Data availability and consistency were good. Some countries did not report figures for each strain of resistant bacteria. National antimicrobial consumption rates (2013) varied from ≤ 13 DDD (Estonia, the Netherlands and Sweden) to ≥ 30 DDD (France, Greece and Romania) per 1000 inhabitants per day. National antimicrobial resistance rates (hospital isolates, 15 species) also varied from <6.1% (Finland, Iceland and Sweden) to > 37.2% (Bulgaria, Greece, Romania and Slovakia). National antimicrobial consumption rates (2013) showed strong to moderate correlation with national hospital antimicrobial resistance rates (2014) in 19 strains of bacteria (r =0.84 to r =0.39). Some countries defied the trend with high consumption and low resistance (France, Belgium and Luxembourg) or low consumption and high resistance (Bulgaria, Hungary and Latvia).
Conclusions
We found associations between national community antimicrobial consumption and national hospital antimicrobial resistance across a wide range of bacteria. These associations were not uniform. Different mechanisms may drive resistance in hospital-based invasive infections. Future research on international variations in antimicrobial resistance should consider environmental factors, agricultural use, vaccination policies and prescribing quality.



Outer membrane protein A contributes to antimicrobial resistance of Acinetobacter baumannii through the OmpA-like domain

2017-07-24

Abstract
Objectives
Acinetobacter baumannii outer membrane protein A (AbOmpA) is involved in bacterial pathogenesis. However, the role of AbOmpA in the antimicrobial resistance of A. baumannii has not been fully elucidated. This study aimed to investigate the role of the OmpA-like domain of AbOmpA in the antimicrobial resistance of A. baumannii.
Methods
The MICs of antimicrobial agents for the WT A. baumannii ATCC 17978, ΔompA mutant, OmpA-like domain-deleted (amino acids 223–356) AbOmpA mutant and single-copy ompA-complemented strain were determined by the Etest method. The MICs of antimicrobial agents for MDR strain 1656-2 and its ΔompA mutant strains were also determined.
Results
The ΔompA mutant strain of ATCC 17978 was more susceptible to trimethoprim (>5.3-fold) and other antimicrobial agents tested (<2.0-fold), except tigecycline, than the WT strain. The ΔompA mutant strain of 1656-2 was more susceptible to trimethoprim (>4.0-fold), tetracycline (2.3-fold) and other antimicrobial agents (<2.0-fold), including tigecycline, colistin and imipenem, than the WT strain. The MICs of gentamicin, imipenem and nalidixic acid for the WT ATCC 17978 and ΔompA mutant strains were decreased in the presence of an efflux pump inhibitor. A mutant strain of ATCC 17978 with the OmpA-like domain of AbOmpA deleted was more susceptible (≥2.0-fold) to substrates of the resistance–nodulation–division efflux pumps, including aztreonam, gentamicin, imipenem and trimethoprim, than the WT strain.
Conclusions
This study demonstrates that AbOmpA contributes to the antimicrobial resistance of A. baumannii through the OmpA-like domain.



In vitro and in vivo efficacies of novel carbazole aminoalcohols in the treatment of cystic echinococcosis

2017-07-24

Abstract
Objectives
Cystic echinococcosis (CE), caused by the cestode Echinococcus granulosus, is a worldwide chronic zoonosis. Current chemotherapeutic options are limited to albendazole and mebendazole, which only exert parasitostatic effects and have to be administered at high dosages for long periods. In an effort to find alternative treatment options, the in vitro and in vivo efficacies of novel carbazole aminoalcohols were evaluated.
Methods
Carbazole aminoalcohols were tested against E. granulosus protoscoleces in vitro and metacestodes ex vivo. The in vivo chemotherapeutic effect of representative compounds was assessed in experimentally infected mice. Oral and intravenous pharmacokinetic profiles were determined in mice.
Results
The carbazole aminoalcohols exhibited potent protoscolicidal activity with LC50 values ranging from 18.2 to 34.3 μM. Among them, compounds 2 and 24 killed all ex vivo cultured metacestodes at concentrations of 34.3 and 30.6 μM. In vivo studies showed that oral administration of compounds 2 and 24 (25 mg/kg/day) for 30 days led to reductions of 68.4% and 54.3% in parasite weight compared with the untreated group (both groups: P <0.001). Compound 2 (25 mg/kg/day) and compound 24 (50 mg/kg/day) induced significantly higher cyst mortality rates in comparison with that of the albendazole group (both groups: P <0.01). Analysis of cysts collected from compound 2- or 24-treated mice by transmission electron microscopy revealed a drug-induced structural destruction. The structural integrity of the germinal layer was lost, and the majority of the microtriches disappeared. Pharmacokinetic profiling of compounds 2 and 24 revealed low clearance and decent oral bioavailability (>70%).
Conclusions
Our study identifies carbazole aminoalcohols as a class of novel anti-CE agents. Compounds 2 and 24 represent promising drug candidates in anti-CE chemotherapy.



A compendium of small molecule direct-acting and host-targeting inhibitors as therapies against alphaviruses

2017-07-21

Abstract
Alphaviruses were amongst the first arboviruses to be isolated, characterized and assigned a taxonomic status. They are globally widespread, infecting a large variety of terrestrial animals, birds, insects and even fish. Moreover, they are capable of surviving and circulating in both sylvatic and urban environments, causing considerable human morbidity and mortality. The re-emergence of Chikungunya virus (CHIKV) in almost every part of the world has caused alarm to many health agencies throughout the world. The mosquito vector for this virus, Aedes, is globally distributed in tropical and temperate regions and capable of thriving in both rural and urban landscapes, giving the opportunity for CHIKV to continue expanding into new geographical regions. Despite the importance of alphaviruses as human pathogens, there is currently no targeted antiviral treatment available for alphavirus infection. This mini-review discusses some of the major features in the replication cycle of alphaviruses, highlighting the key viral targets and host components that participate in alphavirus replication and the molecular functions that were used in drug design. Together with describing the importance of these targets, we review the various direct-acting and host-targeting inhibitors, specifically small molecules that have been discovered and developed as potential therapeutics as well as their reported in vitro and in vivo efficacies.