Archive for April 10, 2016
Evaluation of Oxacillin and Cefoxitin Disk and MIC Breakpoints for Prediction of Methicillin Resistance in Human and Veterinary Isolates of Staphylococcus intermedius Group
Journal of Clinical Microbiology March 2016 V.54 N.3 P.535-542
Bacteriology
T. Wu, C.-A. D. Burnham, L. F. Westblade, J. Dien Bard, S. D. Lawhon, M. A. Wallace, T. Stanley, E. Burd, J. Hindler, and R. M. Humphries
aUCLA David Geffen School of Medicine, Los Angeles, California, USA
bLandstuhl Regional Medical Center, Landstuhl, Germany
cWashington University School of Medicine, St. Louis, Missouri, USA
dWeill Cornell Medical College, New York, New York, USA
eChildren’s Hospital of Los Angeles, Los Angeles, California, USA
fVeterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, Texas, USA
gEmory University School of Medicine, Atlanta, Georgia, USA
hEmory Antibiotic Resistance Center, Atlanta, Georgia, USA
- M. Humphries, rhumphries@mednet.ucla.edu.
Staphylococcus pseudintermedius is a coagulase-positive species that colonizes the nares and anal mucosa of healthy dogs and cats.
Human infections with S. pseudintermedius range in severity from bite wounds and rhinosinusitis to endocarditis; historically, these infections were thought to be uncommon, but new laboratory methods suggest that their true incidence is underreported.
Oxacillin and cefoxitin disk and MIC tests were evaluated for the detection of mecA- or mecC-mediated methicillin resistance in 115 human and animal isolates of the Staphylococcus intermedius group (SIG), including 111 Staphylococcus pseudintermediusand 4 Staphylococcus delphini isolates, 37 of which were mecA positive.
The disk and MIC breakpoints evaluated included the Clinical and Laboratory Standards Institute (CLSI) M100-S25 Staphylococcus aureus/Staphylococcus lugdunensis oxacillin MIC breakpoints and cefoxitin disk and MIC breakpoints, the CLSI M100-S25 coagulase-negative Staphylococcus (CoNS) oxacillin MIC breakpoint and cefoxitin disk breakpoint, the CLSI VET01-S2 S. pseudintermedius oxacillin MIC and disk breakpoints, and the European Committee on Antimicrobial Susceptibility Testing (EUCAST) S. pseudintermedius cefoxitin disk breakpoint.
The oxacillin results interpreted by the VET01-S2 (disk and MIC) and M100-S25 CoNS (MIC) breakpoints agreed with the results of mecA/mecC PCR for all isolates, with the exception of one false-resistant result (1.3% of mecA/mecC PCR-negative isolates). In contrast, cefoxitin tests performed poorly, ranging from 3 to 89% false susceptibility (very major errors) and 0 to 48% false resistance (major errors).
BD Phoenix, bioMérieux Vitek 2, and Beckman Coulter MicroScan commercial automated susceptibility test panel oxacillin MIC results were also evaluated and demonstrated >95% categorical agreement with mecA/mecC PCR results if interpreted by using the M100-S25 CoNS breakpoint. The Alere penicillin-binding protein 2a test accurately detected all mecA-positive isolates, although for four isolates, cefoxitin induction was required prior to testing.
These data demonstrate that the cefoxitin surrogate test does not reliably detect the presence of mecA in S. pseudintermedius isolates and that laboratories should perform oxacillin disk or MIC tests of these isolates when they are encountered.
http://jcm.asm.org/content/54/3/535.full.pdf
What’s in a Name? The Impact of Accurate Staphylococcus pseudintermedius Identification on Appropriate Antimicrobial Susceptibility Testing
Journal of Clinical Microbiology March 2016 V.54 N.3 P.516-517
Commentary
Brandi M. Limbago
Division of Healthcare Quality Promotion, Centers for Disease Control and Prevention, Atlanta, Georgia, USA
Bacteria in the Staphylococcus intermedius group, including Staphylococcus pseudintermedius, often encode mecA-mediated methicillin resistance.
Reliable detection of this phenotype for proper treatment and infection control decisions requires that these coagulase-positive staphylococci are accurately identified and specifically that they are not misidentified as S. aureus.
As correct species level bacterial identification becomes more commonplace in clinical laboratories, one can expect to see changes in guidance for antimicrobial susceptibility testing and interpretation.
The study by Wu et al. in this issue (M. T. Wu, C.-A. D. Burnham, L. F. Westblade, J. Dien Bard, S. D. Lawhon, M. A. Wallace, T. Stanley, E. Burd, J. Hindler, R. M. Humphries, J Clin Microbiol 54:535–542, 2016, http://dx.doi.org/10.1128/JCM.02864-15) highlights the impact of robust identification of S. intermedius group organisms on the selection of appropriate antimicrobial susceptibility testing methods and interpretation.
Clustering of Antimicrobial Resistance Outbreaks Across Bacterial Species in the Intensive Care Unit
Clinical Infectious Diseases July 1, 2013 V.57 N.1 P.65-76
Editor’s Choice
Anne L. M. Vlek, Ben S. Cooper, Theodore Kypraios, Andy Cox, Jonathan D. Edgeworth, and Olga Tosas Auguet
1Centre for Clinical Infection and Diagnostics Research, Department of Infectious Diseases, King’s College London and Guy’s and St Thomas’ NHS Foundation Trust, London, United Kingdom
2Medical Microbiology, University Medical Centre Utrecht, the Netherlands
3Centre for Clinical Vaccinology and Tropical Medicine, Nuffield Department of Clinical Medicine, University of Oxford, United Kingdom
4Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand
5School of Mathematical Sciences, University of Nottingham
6Department of Infectious Disease Epidemiology, London School of Hygiene and Tropical Medicine, London, United Kingdom
Background
here are frequent reports of intensive care unit (ICU) outbreaks due to transmission of particular antibiotic-resistant bacteria. Less is known about the burden of outbreaks of resistance due to horizontal transfer of mobile genetic elements between species. Moreover, the potential of existing statistical software as a preliminary means for detecting such events has never been assessed. This study uses a software package to determine the burden of species and resistance outbreaks in 2 adjacent ICUs and to look for evidence of clustering of resistance outbreaks consistent with interspecies transmission of resistance elements.
Methods
A retrospective analysis of data from 2 adjacent 15-bed adult ICUs between 2002 and 2009 was undertaken. Detection of bacterial species-groups and resistance outbreaks was conducted using SaTScan and WHONet-SaTScan software. Resampling and permutation methods were applied to investigate temporal clustering of outbreaks.
Results
Outbreaks occurred for 69% of bacterial species-groups (18/26), and resistance outbreaks were detected against 63% of antibiotics (10/16). Resistance outbreaks against 7 of 10 antibiotics were observed in multiple species-groups simultaneously and there was evidence of inter–species-group dependence for 4 of 7 antibiotics; background temporal changes in resistance did not explain the temporal aggregation of outbreaks in 3 of 7 antibiotics.
Conclusions
Species outbreaks occurred for the majority of bacteria commonly identified in the ICU. There was evidence for frequent temporal clustering of resistance outbreaks consistent with interspecies transmission of resistance elements. Wider application of outbreak detection software combined with targeted sequencing of bacterial genomes is needed to understand the contribution of interspecies gene transfer to resistance emergence. Outbreaks of bacterial species occur for the majority of bacteria commonly identified in the intensive care unit. This study provides evidence for frequent temporal clustering of resistance outbreaks consistent with interspecies transmission of resistance elements.
http://cid.oxfordjournals.org/content/57/1/65.full.pdf
Effect of Previous-Year Vaccination on the Efficacy, Immunogenicity, and Safety of High-Dose Inactivated Influenza Vaccine in Older Adults
Clinical Infectious Diseases May 1, 2016 V.62 N.9 P.1092-1099
Carlos A. DiazGranados, Andrew J. Dunning, Corwin A. Robertson, H. Keipp Talbot, Victoria Landolfi, and David P. Greenberg
1Sanofi Pasteur, Swiftwater, Pennsylvania
2Vanderbilt University Medical Center, Nashville, Tennessee
3Department of Pediatrics, University of Pittsburgh School of Medicine, Pennsylvania
Background
High-dose inactivated influenza vaccine (IIV-HD) is an alternative to the standard-dose inactivated influenza vaccine (IIV-SD) in the United States for influenza prevention in older adults. IIV-HD improved efficacy relative to IIV-SD in a randomized controlled trial. Recent observational studies suggest that previous influenza vaccination may influence the immunogenicity and effectiveness of current-season vaccination.
Methods
The original study was a double-blind, randomized trial comparing IIV-HD to IIV-SD in adults aged ≥65 years over 2 influenza seasons. A subset of year 1 (Y1) participants reenrolled in year 2 (Y2), receiving vaccine by random assignment in both years. We evaluated the effect of Y1 vaccination on Y2 relative vaccine efficacy (VE), immunogenicity (hemagglutination inhibition [HAI] titers), and safety among reenrolled participants.
Results
Of 14 500 Y1 participants, 7643 reenrolled in Y2. Relative to participants who received IIV-SD both seasons, VE was higher for IIV-HD vaccinees in Y2 (28.3% overall; 25.1% for Y1 IIV-HD, Y2 IIV-HD; and 31.6% for Y1 IIV-SD, Y2 IIV-HD). In multivariate logistic regression models, Y1 vaccine was not a significant modifier of Y2 VE (P = .43), whereas Y2 IIV-HD remained significantly associated with lower influenza risk (P = .043). Compared to administration of IIV-SD in both years, postvaccination HAI titers were significantly higher for patterns that included IIV-HD in Y2. No safety concerns were raised with IIV-HD revaccination.
Conclusions
IIV-HD is likely to provide clinical benefit over IIV-SD irrespective of previous-season vaccination with IIV-HD or IIV-SD. IIV-HD consistently improved immune responses, and no safety concerns emerged in the context of IIV-HD revaccination.
http://cid.oxfordjournals.org/content/62/9/1092.full.pdf
