Determination of vancomycin and methicillin resistance in clinical isolates of Staphylococcus aureus in hospitals of Ilam city

In this study, using the phenotypic and genotypic methods, oxacillin susceptibility in Staphylococcus aureus (S. aureus) strains isolated from patients at two government hospitals in Ilam, Iran was tested.

Out of 200 S. aureus isolates from different human clinical specimens consisting of blood (31%), wound (20%), urine (21%), catheters (7%), sputum (12%), others (9%) were collected. The methicillin resistant S. aureus isolates were investigated using disk diffusion methods and oxacillin (1μg) and cefoxitin (30μg), on Mueller-Hinton agar were used, and MecA and vanA genes were detected by PCR. In addition, the isolates were tested for their antibiogram profiles.

Among 200 S. aureus strains included in this study, 35.96% were MRSA. The percentage of resistance by disk diffusion method was as below: penicillin 85.96%, vancomycin 0%, ampicillin 87.71%, gentamicin 48.25% erythromycin 54.25%, clindamycin 32.45%, amikacin 21.05%, ciprofloxacin 42.10%, tetracycline 51.75% and co-trimoxazole 42.10%. Phenotyping method by disk diffusion method using oxacillin and cefoxitin for detecting of MRSA showed sensitivity and specificity of about 33.33% and 35.96%, respectively. Presence of MecA and vanA genes in MRSA isolates by PCR were 35.96% and 0%, respectively. The oxacillin and cefoxitin disk diffusion methods showed 92.68% and 100% sensitivity, respectively, and 98.8% specificity.

Our finding showed that, the cefoxitin disk diffusion method is better in compared to the oxacillin disk diffusion similar to results from detecting of MecA gene in PCR as a golden test.