Conventional versus molecular tests (Multiplex PCR and PCR mecA gene) for detection of methicillin resistant Staphylococcus aureus

Abstract

In this study, for detection of methicillin-resistant S. aureus (MRSA), a mecA multiplex PCR-based amplification was compared with the 1 µg oxacillin disk diffusion test, detection of minimal inhibitory concentration (MIC), and screening in agar with 4% NaCl and 6 µg/mL oxacillin. Among 24 isolates obtained from blood, mecA gene was detected in only 16 (66.7%) isolates by multiplex PCR. The MIC test showed a range of resistance to oxacillin from 0.19 to 512 µg/mL, among these isolates. Data obtained by screening and dilution tests showed that sensitivity to methicillin was 80.0% and 72.8%, respectively, when compared with the presence of mecA gene (multiplex). All isolates, including the negatives, when revaluated for mecA gene by PCR were positive. β-lactamase production was positive for 20/25 isolates (80.0%). About ¼ of patients died dispite most of them (83.3%) were adequately treated. The simultaneous identification of the bacteria and determination of this susceptibility to antibiotics are necessary for the choice of empiric antibiotic therapy in suspected staphylococcal sepse, but is important to considering the sensibility, specificity and validation of the available kits.

Molecular detection of methicillin resistant Staphylococcus aureus harbouring β- lactamase resistance genes isolated from different sources of infections

“…Furthermore, the findings of the current study were inconsistent with other researchers who stated that 83.3% of the S. aureus isolates were producing β-lactamase and it was postulated that despite the expression of the mec A gene which can be considered as an essential mechanism of resistance, other mechanisms alone or in combination have been found in Staphylococci. 16 Controversial data are still argued about the reliability of the ordinary susceptibility testing techniques, including disk diffusion and agar dilution tests, in detecting methicillin resistant staphylococci. 17 When uni-plex PCR was considered, the results of the present study came in line with another which revealed that all phenotypically identified MRSA isolates showed positive PCR yield for mec A gene but contradictory findings appeared as far as Multiplex PCR was considered.…”

Phenotypic methods for determination of methicillin resistance in Staphylococcus spp. from health care workers

“…With the advantage of PCR over phenotypic methods with rapid turnaround time, measures to control infection can be taken more quickly (31) . Some studies have shown discrepancies in accuracy between the phenotypic tests and molecular detection of the mecA gene by PCR, considered the gold standard method (3,24,30) .…”

Authors' reply: Emergence of antibiotic-resistant bacterial strains, methicillin-resistant Staphylococcus aureus and extended spectrum β-lactamases, and multi-drug resistance are problems similar to global warming

“…Regarding the detection of resistance genes described by Dr. Bhattacharya, in our laboratory 11 , we compared multiplex polymerase chain reaction (PCR) assays for the detection of resistance genes. We used classical methods to determine the susceptibility to antibiotics.…”