Evaluation of Five Phenotypic Methods for Detection of Methicillin Resistant Staphylococcus aureus (MRSA)

  BackgroundandObjectives:RapidandaccuratedetectionofmethicillinresistantStaphylococcus aureus (MRSA) is an important role of clinical microbiology laboratories to avoid treatment failure. The aim of this study was to compare conventional methods against the E-test minimum inhibitory concentration (MIC) method to determine the best phenotypic method. Materials and Methods: Methicillin resistance was studied among clinical isolates of S. aureus from April to October 2009 in Milad Hospital of Tehran. These methods included E-test MIC, oxacillin screen agar, oacillin disk diffusion, cefoxitin disk diffusion, and CHROMagar- MRSA methods. Results: Out of 294 isolates of S. aureus, one hundred and six (36%) strains of MRSA were isolated from clinical specimen. Oxacillin screen agar and CHROMagar-MRSA showed both 110 MRSA isolates. The sensitivity and specificity for these two methods were 100% and 97.9%, respectively. The sensitivity and specificity of oxacillin disk diffusion method was similar to those of oxacillin screen and CHROMagar-MRSA. One hundred and eight strains of S. aureus were MRSA by cefoxitin disk diffusion method. The sensitivity and specificity of cefoxitin disk diffusion method was 100% and 98.1% respectively. All isolates including MRSA were susceptible to vancomycin. Nearly al MRSA isolates were resistant to erythromycin, clindamycin, chloramphenicol, tetracycline, ceftriaxone and ciprofloxacin. Conclusion: All phenotypic methods had high sensitivity and specificity for detection of MRSA. However, cefoxtin disk diffusion method in comparison to other methods had higher specificity.