Antimicrobial Resistance Profiles of Staphylococcus aureus Isolated in 13 Korean Hospitals

Abstract

Background : There has been a nationwide increase in infections caused by Staphylococcus aureus resistant to multiple antimicrobial agents in Korea. Although nationwide antimicrobial resistance profiles have been reported recently by analysing routine antimicrobial test results, a more extensive resistance profile survey including those agents that are not used routinely is required for the inferring the mechanism of antimicrobial resistance. We assessed the resistance profiles of a variety of antimicrobial agents on Korean nationwide collection of S. aureus strains and analyzed the profiles according to methicillin resistance. Methods : We collected a total of 253 clinical isolates of S. aureus from 13 clinical laboratories over the country during a month in 2002. Antimicrobial susceptibility testings were performed with 21 antimicrobial agents by disk diffusion method. Methicillin-resistant S. aureus (MRSA) isolates were also confirmed by the PCR detection of mecA gene. Results : More than 90% of MRSA strains were resistant to the following antimicrobial agents tested: -lactams (92.0-98.3%), gentamicin (92.5%), tobramycin (94.9%), erythromycin (96.6%), and ciprofloxacin (94.3%). But only 0-29% of methicillin-susceptible S. aureus (MSSA) strains were resistant to those agents. MRSA and MSSA strains were respectively resistant to chloramphenicol in 4.0% and 2.5%, rifampin in 12.1% and 1.3%, trimethoprim-sulfamethoxazole in 22.4% and 1.3%, and amikacin in 51.7% and 3.8%. No isolates were resistant to vancomycin and teicoplanin. Falsely susceptible results against beta-lactams in MRSA ranged from 1.7-7.5%. No significant differences in susceptibility were noted against the agents within the same classes such as macrolide and fluoroquinolone. The PCR results of mecA gene correlated 100% with the results of oxacillin disk diffusion test. Conclusions : Methicillin resistance in S. aureus was an indication of resistance against -lactams, gentamicin, tobramycin, macrolide, and fluoroquinolone in Korea. However, MRSA still retained the susceptibility to chloramphenicol, rifampin, and trimethoprim-sulfamethoxazole. This study may provide antimicrobial resistance profiles necessary for the understanding of antimicrobial resistance mechanisms of S. aureus.