Evaluation of GeneXpert® system for detection of methicillin-resistant Staphyloccocus aureus in clinical samples

Infections caused by methicillin-resistant Staphyloccocus aureus strains (MRSA) have reached epidemic proportions globally, being the major cause of nosocomial infections. Rapid identification of MRSA in nasal swabs or in clinical samples is considered a useful strategy for control and treatment of these infections. GeneXpert system (Cepheid Europe,Vira-Solelch, Maurence-Scopont-France) can detect by real-time PCR in approximately one hour methicillin-resistant S. aureus or coagulase-negative staphylococci (CoNS) in clinical samples, in comparison with 24 hours for the culture or 48 hours for the antimicrobial susceptibility testing. In this study GeneXpert system was compared with traditional tests for MRSA detection in nasal swabs, bloodcultures and surgical wound swabs. Materials and methods. Eighteen nasal swabs, 23 blood-cultures and 13 surgical wound swabs were tested. The samples were cultured on blood-agar and mannitol-salt agar. Identification of isolates was carried out with traditional tests (Gram staining, catalase, coagulase) and automatic Phoenix system. Methicillin-susceptibility was evaluated according to 2010 CLSI guidelines. GeneXpert system was performed according to manufacturers instructions, by using the specific kits and methicillin-resistance was detected by amplification of the genic sequences spa, SCC e mecA. Results. The results showed a 100% accordance between GeneXpert system and traditional tests for detection of methicillin-resistant staphylococci. In particular, among 18 nasal swabs, no MRSA was detected, while 1 bloodculture (4.3%) and 4 surgical wound swabs (30.7%) were positive for MRSA. Conclusions. GeneXpert system allows a rapid detection of MRSA in clinical samples and shows the same sensitivity and specificity as traditional tests. Therefore, it represents a further effective diagnostic method for prevention and treatment of nosocomial infections due to methicillin-resistant staphylococci.