Prevalence and molecular characterization of plasmid-mediated beta-lactamase genes among nosocomial Staphylococcus aureus   isolated in Taiwan

Purpose: To analyze the drug susceptibility phenotypes and the patterns of plasmid-mediated β-lactamase genes among nosocomial Staphylococcus aureus drug resistance isolates in Taiwan.
Methods: The antibiotic susceptibilities of 617 clinical Staphylococcus aureus isolates collected from 2005 - 2009 from Chiayi Christian Hospital (Chiayi, Taiwan) were examined in vitro against 8 antimicrobial agents using agar diffusion method. Among the clinical isolates, 114 strains of methicillin-sensitive Staphylococcus aureus and 45 strains of methicillin-resistant Staphylococcus aureus (MRSA) isolates were selected for plasmid profile analysis. The patterns of β-lactamase genes presented in plasmids were investigated by polymerase chain reaction analysis.
Results: Most test strains were resistant to multiple antibiotics, particularly for the traditional agents such as ampicillin, penicillin, cephalexin and kanamycin. Plasmid profile analysis revealed that up to 36 % of the clinical strains harbored plasmids and were able to develop multi-drug resistant. Among them, most of the isolates harbored at least one plasmid (range 1 – 7) with a size range of 2.3 to 23 Kb. Among the several types of β-lactamases, blaTEM was the most prevalent.
Conclusion: The results obtained from this study can serve as a valuable reference for the future control for clinical antibiotic resistant strains and more thorough discussions on resistance mechanisms.

Keywords
Staphylococcus aureus; Antibiotic susceptibility; Nosocomial pathogens; Plasmid profile; β-lactamases