Clonal Types and Antimicrobial Susceptibilitiy Patterns in Methicillin-Resistant Staphylococcus aureus Isolates from a Korean Hospital

ABSTRACT

A total of 54 non-duplicate methicillin-resistant Staphylococcus aureus (MRSA) isolates from clinical specimens and 3 MRSA isolates from healthy medical staffs were obtained from Kyungpook National University Hospital. They were analyzed for clonal types by multilocus sequence typing, protein A gene (spaA) typing, the staphylococcal cassette chromosome mec (SCCmec) typing, and pulsed-field gel electrophoresis (PFGE). The MRSA isolates were examined for antimicrobial susceptibility. Clinical MRSA isolates were classified into 4 clonal complexes, 4 sequence types (STs), 5 spaA types, 4 PFGE patterns, and 3 SCCmec types with variants. On the basis of ST, ST239 (n=25) and ST5 (n=24) were the most frequently encountered. MRSA isolates belonging to ST239 were genotypically homogenous, while those belonging to ST5 showed variations in spaA and SCCmec types. Of the 3 MRSA isolates from healthy medical staffs, one was genotypically identical to MRSA isolates belonging to ST5 and the other two ST239. All MRSA isolates were susceptible to vancomycin and teicoplain. Only 4% of isolates were resistant to rifampin, while 91% of isolates were resistant to ciprofloxacin. The resistance rate of MRSA isolates belonging to ST239 against trimethoprim-sulfamethoxazole (SXT) was significantly higher than that of the isolates belonging to ST5 (76% vs 0%, p<0.001). In summary, ST239 and ST5 were responsible for most MRSA infections and healthy medical staffs also carried these MRSA strains. The susceptibility of the ST239 clone against SXT, which was commonly used for oral therapy to treat MRSA infection, was significantly different from the ST5 clone.