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.