Prevalence and pattern of antibiotic sensitivity of methicillin-sensitive and methicillin-resistant staphylococcus aureus in Shiraz-Iran

ABSTRACT

There is a growing concern about the rapid rise in resistance of Staphylococcus aureus to antimicrobial agents. To determine the prevalence and pattern of antibiotic sensitivity among methicillin-resistant and -sensitive S.aureus in Shiraz, south of Iran. One hundred and six S. aureus isolates from patients with staphylococcal infections were collected. The isolates were screened for methicillin-resistance by minimum inhibitory concentration [MIC] determination and agar screen plate. Detection of acquired resistance was accomplished by addition of a beta -lactamase inhibitor to the test media. Tolerance was detected by determination of minimum bactricidal concentration [MBC]/MIC ratio. The frequency of intrinsic-resistant S. aureus was 33.0% [90% in isolates from burn unit patients]. Acquired-resistant and tolerant isolates comprised 4.7% and 0.9% of all isolates respectively. None of the isolates showed MOD-type resistance [for "modified" penicillin binding proteins [PBPs]]. The pattern of resistance to 13 antibiotics were determined by disk diffusion method. None of the intrinsic-resistant isolates were resistant to vancomycin or rifampin but the frequency of resistance to other compounds was high. The methicillin-sensitive and acquired-resistant isolates were highly sensitive to all tested antibiotics except penicillin. In this study, methicillin-resistance proved to be a useful marker in selecting appropriate antimicrobial agents for treatment of infections caused by S. aureus. Changing pattern of resistance of S.aureus makes its periodic surveillance [each 3 to 4 years once] mandatory