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Phenotypic detection of methicillin resistance in Staphylococcus aureus by disk diffusion testing and Etest on Mueller-Hinton agar.

ABSTRACT: Cefoxitin is increasingly recommended for detection of methicillin resistance in Staphylococcus aureus (MRSA) when using disk diffusion testing. In this study, 95 mecA-negative S. aureus isolates and a highly genetically diverse collection of mecA-positive S. aureus types (n=50) were used to investigate the influence of technical factors such as disk potency, incubation time, and temperature on Mueller-Hinton agar. The use of cefoxitin MIC testing by Etest for the same purpose was investigated under similar conditions. For disk diffusion, the accuracy was high at both 35 degrees C and 36 degrees C using overnight incubation, while incubation at 30 degrees C or 37 degrees C was associated with slightly lower accuracy. Increasing incubation times from 18 to 24 h did not improve accuracy at either temperature. Cefoxitin Etest MICs for mecA-positive strains were 6 mg/liter or higher, while cefoxitin Etest MICs for mecA-negative strains were 4 mg/liter, corresponding to S>or=22 mm and Ror=17 mm and R

SUBMITTER: Skov R

PROVIDER: S-EPMC1698388 | biostudies-other | 2006 Dec

REPOSITORIES: biostudies-other

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Disk Diffusion Testing for Detection of Methicillin-Resistant Staphylococci: Does Moxalactam Improve upon Cefoxitin?

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2024-07-10 | GSE253142 | GEO

Evaluation of phenotypic with genotypic methods for species identification and detection of methicillin resistant in Staphylococcus aureus.

Project description:BackgroundPhenotypic methods for the detection of methicillin resistance are inadequate, due to presence of hetero-resistant population and dependence of environmental factors that may affect the phenotypic expression of resistance.AimsPresent study was conducted, to evaluate the efficacy of phenotypic methods for the identification of species and mec-A mediated resistance in S. aureus with polymerase chain reaction (PCR), and to assess the prevalence of the Panton-Valentine leukocidin (pvl) toxin in methicillin resistant S. aureus (MRSA) and overall S.aureus population.Materials and methodsA total of 200 clinical isolates of Staphylococci were subjected to phenotypic and genotypic methods for the species identification and detection of MRSA.ResultsThe specificity and sensitivity of conventional methods in the detection of S.aureus, was found to be 100 and 97.59% respectively. However, the performance of phenotypic methods in the detection of MRSA were: Oxacillin disc diffusion (DD)-sensitivity 70.58%, specificity 75.75%; cefoxitin DD-sensitivity 86.27%, specificity 83.33%; and oxacillin agar dilution-sensitivity 92.15%, specificity 90.90%. PVL gene was detected in all mec-A positive isolates irrespective of their types.ConclusionPhenotypic methods still preferred for the species identification, but for the reliable detection of MRSA an algorithm should include a combination of tests and apply a genotypic method for confirmation of resistance isolates showing discrepant results. Considering the high prevalence of PVL-MRSA, we recommend PCR as assay, as it has an advantage of simultaneous detection of mec-A and pvl genes by multiplex PCR.

| S-EPMC3678700 | biostudies-literature

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