Susceptibility testing of vancomycin, daptomycin and linezolid against methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) has been recognized as a major cause of healthcare-associated and community-acquired infections. The resistant genes of MRSA can be transferred very quickly between different strains. This study aimed to determine in vitro antimicrobial susceptibility and the minimal inhibitory concentration (MIC) of vancomycin, daptomycin and linezolid against methicillin-resistant Staphylococcus aureus (MRSA) from various clinical specimens of in- and out-patients and to study the antimicrobial susceptibility patterns. A total of 330 isolates of MRSA (in-patients = 295 isolates and out-patients = 35 isolates) from clinical specimens were obtained from Microbiology Laboratory, Faculty of Medicine, Vajira Hospital during April 2013 to March 2014. MIC of vancomycin and linezolid were performed by agar dilution technique and daptomycin by agar gradient diffusion technique. All of isolates were susceptible to vancomycin, daptomycin and linezolid. These results indicated that vancomycin, daptomycin and linezolid showed good activity against 330 MRSA tested (100% susceptibility). Therefore, they may be the drug of choices for MRSA treatment.