Comparison of methicillin-resistant Staphylococcus aureus strains isolated in 2003 and 2008 with an emergence of multidrug resistant ST22: SCCmec IV clone in a tertiary hospital, Malaysia.

Background/purpose: Infections caused by methicillin-resistant Staphylococcus aureus (MRSA) continue to be a problem for clinicians worldwide. The objective of this study was to determine the changes in antibiograms of MRSA and their genotypic characteristics.

Methods: The antibiograms of 162 MRSA isolates (52 from 2003 and 110 from 2008) from a tertiary hospital were analyzed by antimicrobial susceptibility tests, the Panton-Valentine leukocidin (PVL) and staphylococcal cassette chromosome mec (SCCmec) types were determined by polymerase chain reaction, and genetic relatedness by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST).

Results: All the isolates were sensitive to vancomycin. Resistance to ciprofloxacin, clindamycin, erythromycin, and gentamicin remained high throughout the study period, although a small decrease was observed in 2008 for ciprofloxacin (96% to 90%) and gentamicin (90% to 83%). Similarly, a slight decrease in resistance toward fusidic acid (10% to 9%), linezolid (2% to 1%), rifampicin (8% to 4%), and teicoplanin (4% to 0%) was observed between 2003 and 2008. In contrast, there was a significant increase (p < 0.05) in resistance rates toward trimethoprim-sulfamethoxazole, netilmicin, and tetracycline between 2003 and 2008. Ninety-six percent of the isolates from both 2003 and 2008 were multidrug resistant. Three SCCmec types (SCCmec type III, 90%; SCCmec type IV, 9%; SCCmec V, 1%) were observed. SCCmec type IV (n = 15) and pvl gene (n = 3) were detected in 2008 isolates but not in 2003 isolates. Most of the SCCmec type IV isolates (12 of 15) belonged to sequence type 22 (ST22) and were resistant to erythromycin and ciprofloxacin, with 11 being multidrug resistant. Most of the isolates were genetically related (F > 0.8) as determined by PFGE. Some isolates from 6 years apart shared similar PFGE profiles, indicating the persistence of a particular genotype. Five STs (ST239, ST772, ST22, ST6, and ST1178) were identified among the 2008 isolates but only one ST (ST239) was observed in 2003 isolates.

Conclusion: Vancomycin remains the most active agent in vitro against S. aureus infection followed by linezolid and teicoplanin. The prevalence of resistance to fluoroquinolones, aminoglycosides (netilmicin), and tetracyclines had increased over the years. The Malaysian multidrug-resistant MRSA isolates were mostly SCCmec type III and ST239, although SCCmec type IV: ST22 is gaining importance. There was a correlation between resistotypes and PFGE profiles.