Comparison of PCR and phenotypic methods for the detection of methicillin resistant Staphylococcus aureus

Abstract

Background and Objectives: Resistance to methicillin in methicillin resistant strains of Staphylococcus aureus (MRSA) is due to the presence of mec-A gene ,which encodes a low affinity penicillin binding protein (PBP)-2a or PBP2. Accurate and rapid identification of MRSA in clinical specimens is essential for timely decision on effective treatment. The aim of the study was to compare three different methods for detection of MRSA namely cefoxitin disc diffusion, CHROM agar MRSA and VITEK-2 susceptibility with PCR which is the gold standard reference method and to find the antibiotic susceptibility pattern of these isolates by VITEK-2.
 Materials and Methods: A Total of 100 non-duplicate S. aureus isolates were collected from different clinical samples among both outpatient and inpatients. Detection of MRSA among these isolates was done by cefoxitin disc diffusion, VITEK-2, CHROM agar MRSA and PCR.
 Results: The sensitivity and specificity of cefoxitin disc diffusion and Vitek was found to be 97.2% and 100%, while that of CHROM agar was found to be 100% and 78.6%. The overall prevalence of MRSA in our study by PCR was 72%.
 Conclusion: Based on the findings in our study, isolates which show cefoxitin zone diameter < 22 mm can be reported as MRSA. However, those isolates which have a zone diameter between 22-24 mm, should ideally be confirmed by PCR.

Evaluation of in-house cefoxitin screening broth to determine methicillin-resistant staphylococci

“…Accurate and rapid detection of MRS results support effective antimicrobial therapy, immediate patient isolation, and appropriate disinfection measures. Several methods for the detection of MRSA include latex agglutination assay, CHROM agar, VITEK, MALDI-TOF mass spectrometry, and PCR [14]. Although some of these methods are rapid, easy to perform, and are accurate in identification or detection, many of these methods are high in cost and have a high level of sophistication that requires operator experience and skill and special instrumentation.…”

Recent Developments in Phenotypic and Molecular Diagnostic Methods for Antimicrobial Resistance Detection in Staphylococcus aureus: A Narrative Review

“…Using gold-standard methods, 72 MRSA and 28 MSSA were identified and the sensitivity and specificity of the chromogenic media for MRSA detection were 100% and 78.6%, respectively. Six false-positive MRSA were identified by the chromogenic media after 24 and 48 h of incubation; those six isolates were confirmed to be MSSA using other phenotypic methods [ 28 ]. In another study, the authors investigated 48 S. aureus subcultures to determine their methicillin resistance using chromogenic MRSA (RTA Laboratories, Kocaeli, Turkey).…”

“…Indeed, both those false negatives were detected as MRSA by VITEK 2 and chromogenic agar. The author suggested that in the case of a borderline inhibition zone diameter, a second confirmatory test might be necessary [ 28 ]. The disk diffusion method is a gold-standard method, and is accurate, reliable, easy to perform and low cost.…”

“…They identified 2 false-negative MSSA out of the 72 MRSA identified. One limitation of the study is that the authors compared the performance of a phenotypic test (VITEK 2) with a molecular test ( mecA -PCR, see below), instead of comparing the VITEK 2 with a similar phenotypic method such as the BMD [ 28 ].…”

Predominance of t355/ST152/SCCmec V clonal type among PVL-positive MRSA isolates in a tertiary care hospital in Belgrade, Serbia

“…S. aureus isolates were obtained by standard microbiological techniques. Specimens were cultured on Columbia agar with 5% sheep blood (bioMe ´rieux, France), incubated for 24 hours aerobically at 37˚C, and identified by the tube coagulase test with rabbit plasma (Torlak, Belgrade) and confirmed by MALDI-TOF MS (VITEK MS, bioMe ´rieux) [5,6]. Methicillin resistance in S. aureus strains…”