The aim of the study was to determine the frequency and type of MRSA strains and 
antibiotic susceptibility in Al-Zahra Hospital, Isfahan, Iran. In an analytic 
descriptive survey in 2005 and early 2006, patients admitted to the hospital who 
contracted S. aureus nosocomial infections were enrolled in the study. All 
isolates were identified by the conventional laboratory tests. Minimal 
Inhibitory Concentration (MIC) of oxacillin on isolated bacteria was determined 
by E-Test method. According to Clinical and Laboratory Standard Institute (CLSI) 
criteria all strains with MIC of > or = 4 microg for oxacillin were identified 
as MRSA. Intrinsic high level resistance (mecA positive) and borderline 
oxacillin resistant Staphylococcus aureus (BORSA) were detected by 
amoxicillin-clavulanate E-test strips. Strains with MIC of > or = 4 microg for 
oxacillin and > or = 8 microg for amoxicillin-clavulanate were identified as 
mecA positive MRSA. Other staphylococcus with MIC > or = 4 microg for oxacillin 
and < or = 4 for amoxicillin-clavulanate were identified as mecA negative MRSA 
(BORSA). MIC of vancomycin also was determined on isolated bacteria. Data were 
analyzed by SPSS version 13 and Who net version 5. Out of 134 Staphylococcus 
aureus samples which were isolated from nosocomial infections 90 (67.2%) were 
MRSA. Sixty seven out of 90 (74.5%) MRSA were mecA positive and 23 out of 90 
(25.5%) were mecA negative (BORSA). Although most of the MRSA strains were 
isolated from surgical site infections, there were no statistically significant 
differences between types of Staphylococcus aureus growing from variant sites of 
infections. Only one (1.49) of the mecA positive MRSA had reduced susceptibility 
to vancomycin but all of the mecA-negative MRSA (BORSA) were sensitive to it. 
Because one fourth of our staphylococcus strains are mecA negative BORSA and 
there is no alternative for vancomycin against mecA positive MRSA and 
Enterococcus spp. in our hospital, vancomycin should be reserved only for life 
threatening infections due to these organisms. Thus MRSA typing should be done 
to choose appropriate antibiotic for optimal treatment of MRSA infections.