Korean J Clin Pathol.  2001 Dec;21(6):505-511.

Detection of mecA, blaZ and aac(6')-aph(2") gene of staphylococci by PCR

• Lee HC
• Kim EH
• Cho HS
• Lee CH
• Kim KD
• Jung BC

Abstract

BACKGROUND
Staphylococci are major nosocomial pathogens and reveal an increase in resistant strains such as methicillin-resistant Staphylococcus aureus. For treatment of infection and prevention of dissemination, rapid and reliable identification methods are required but the conventional bacterial identification and susceptibility tests require at least 24 hours. In this study, we evaluated the polymerase chain reaction (PCR) of the antibiotic resistant genes by comparing with the disk diffusion susceptibility test for the detection of resistance to penicillin, oxacillin and gentamicin.
METHODS
A hundred-thirty-five staphylococci including 95 S. aureus and 40 S. epidermidis were from clinical specimens from June to December 2000. Antimicrobial susceptibility tests were done using the NCCLS disk diffusion method. PCRs were performed with primer sets specific for mecA, blaZ and aac(6')-aph(2"). The species-specific PCR was also used to identify S. aureus and S. epidermidis.
RESULTS
All four penicillin-susceptible staphylococci were negative for blaZ and 108 of 131 penicillin resistant-staphylococci were positive for blaZ. The concordance rate for PCR of the blaZ gene and penicillin disk diffusion test was 83.0%. 110 of 115 oxacillin-resistant staphylococci were positive for mecA and all five mecA negative oxacillin-resistant strains were positive for blaZ and have the phenotype beta-Lactamase hyperproducer. One of the oxacillin-susceptible S. aureus was positive for mecA. The concordance rate of PCR for the mecA gene and oxacillin disk diffusion test and those of the aac(6')-aph(2") gene and gentamicin disk diffusion test was 95.6% and 97.8%, respectively. CONCLUSTIONS: The disk diffusion tests misdiagnosed 25% of the mecA negative staphylococci as methicillin-resistant staphylococci (MRS) and lost one of the mecA positive strain. We considered that the detection of the mecA and blaZ gene using the PCR was more useful than the disk diffusion test for detection of methicillin-resistant staphylococci.

Keyword

Staphylococci; PCR; mecA; blaZ; aac(6')-aph(2"); MRS

MeSH Terms

beta-Lactamases
Diffusion
Gentamicins
Methicillin Resistance
Methicillin-Resistant Staphylococcus aureus
Oxacillin
Penicillins
Phenotype
Polymerase Chain Reaction*
Gentamicins
Oxacillin
Penicillins
beta-Lactamases