Staphylococcus aureus is associated with different infections ranging from skin and soft tissue infections to endocarditis and fatal pneumonia. Today, methicillin resistant S. aureus (MRSA) isolates are widely spread in both community and hospitals and are often resistant to several antibiotics, causing high morbidity and mortality worldwide. However, the emergence of vancomycin resistance among MRSA isolates has been perceived as a formidable threat to therapeutic management. Therefore, the present study aimed to determine the frequency and antibiotic susceptibility of S. aureus in human clinical samples collected from Kerman hospitals in Iran. The frequency of MRSA and vancomycin-resistant S. aureus (VRSA) strains was also determined. A total of 455 human clinical samples were collected from Afzalipour and Bahonar Hospitals in Kerman, Iran. The samples were examined for the presence of S. aureus, and the isolates were tested for their susceptibility to antibiotics by the disk diffusion method. MRSA isolates were detected by a combination of phenotypic (resistance to cefoxitin) and genotypic (mecA gene amplification) methods. Furthermore, VRSA was detected among MRSA strains by testing their susceptibility to vancomycin by broth microdilution method and vancomycin resistant isolates were screened for the presence of vanA gene using PCR. Sixty-five coagulase-positive S. aureus strains were isolated, and the higher isolation rate was from wound samples (47.7%) compared with other sample types. The isolates exhibited high resistance toward tetracycline (69.2%), followed by erythromycin (58.5%), cefoxitin (52.3%), ciprofloxacin and
levofloxacin (47.7%) than other antibiotics. Thirty-four isolates (52.3%) were categorized as MRSA (phenotypically resistant to cefoxitin) and displayed high resistance to tetracycline, followed by erythromycin, ciprofloxacin, levofloxacin, clindamycin, gentamicin, amikacin, and tobramycin compared with methicillin sensitive S. aureus(MSSA) isolates (P0.05). Given the alarming rate of resistance among MRSA isolates, monitoring of antibiotic resistance should be performed to reduce treatment failure in patients with staphylococcal infections. Although vancomycin remains a drug of choice for MRSA, our study suggests that its efficacy may be limited by resistance development.
Key words: Staphylococcus aureus; methicillin; vancomycin; resistance; mecA gene; vanA gene
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