Prevalence and antimicrobial susceptibility of methicillin-resistant Staphylococcus aureus clones: A study at Taksin Hospital, Bangkok, Thailand

Methicillin-resistant Staphylococcus aureus (MRSA) is a common pathogen in human diseases. Thirty-seven clinical clones from different patients were tested for a molecular study of the mecA gene and multilocus sequence types (ST). Total genomic extraction, followed by a polymerase chain reaction (PCR) for DNA amplification with specific primers for mecA, and specific primers for various ST were used. Molecular typing for the study of genetic relationships among clones was performed by enterobacterial repetitive intergenic consensus (ERIC)-PCR. Antimicrobial susceptibility testing for all clones to 9 drugs was performed by the disk diffusion and vancomycin E-test. The presence of mecA was detected in all clones. The most common ST was MRSA-ST30, accounting for 81.1% of all MRSA tested, followed by MRSA-ST8/ST97/ST779 (8.1%), MRSA-ST239 (2.7%) and MRSA-nontypeable clones (8.1%). Molecular typing by ERIC-PCR demonstrated DNA fingerprints with corresponding results with sequence types. All clones were susceptible (70-100%) to fosfomycin, fusidic acid, gentamicin, tetracycline, trimethoprim-sulfamethoxazole and vancomycin [minimal inhibitory concentration (MIC) range, MIC₅₀ and MIC₉₀ were 0.25-1.0, 0.5 and 0.75 µg/ml, respectively by using E-test] but resistant to ciprofloxacin, clindamycin and erythromycin. Inducible macrolide, lincosamide-type B streptogramin resistance (iMLSB) phenotype was 5.4% while constitutive MLSB phenotype was 91.9%. For MRSA-ST30 clones, 96.7% were multi-drug resistant (MDR) with the most common pattern being resistant to ciprofloxacin, clindamycin and erythromycin. These results suggest the importance of MRSA in the field of epidemiology at a hospital in Thailand.