Antimicrobial susceptibility, virulence factors and biofilm formation among Staphylococcus aureus isolates from hospital infections in Kerman, Iran

Objective: The aims of present study were to determine the antimicrobial susceptibility, virulence factors and biofilm formation among MRSA hospital isolates of Staphylococcus aureus. Methods: Thirty non-repetitive strains of S. aureus isolated from three hospitals in Kerman, Iran. Antimicrobial sus­ceptibility was determined by disk diffusion breakpoints method according to CLSI guideline. The minimum inhibitory concentration (MIC) of vancomycin and methicillin were measured by the broth microdilution and E-test procedures. Virulence factors (protease, DNase, lecithinase, capsule and hemolysis) associated with the above isolates was studied. Biofilm was quantified by microtiter technique. Results: In total, 14 (46.7%) S. aureus were isolated from lower respiratory tract, six (20.0%) from urinary tract and re­maining 10 (33.3%) were recovered from wounds, blood and orthopedic patients. All of the isolates were susceptible to tigecycline, eight (26.7%) were found to be resistant to methicillin (MRSA) and 4 (13.3%) showed reduced susceptibility to vancomycin. No any vancomycin resistant isolate was detected (p≤0.05). MIC results showed that four of the isolates (13.3%) exhibited MIC 4 μg/mL to vancomycin while, five (16.6%) demonstrated MIC 32 μg/mL to methicillin. The iso­lates were also resistant to amoxicillin/clavulanic acid, tetracycline and tobramycin. It was found that, six (75 %) of MRSA strains produced lecithinase, seven (96.7%) demonstrated protease and DNase activities as compared to MSSA isolates. Biofilm analysis revealed that twenty (66.7%) isolates formed strong, seven (23.3%) formed moderate and three (10.0%) had weak biofilm. Conclusion: From the results, it can be concluded that, treatment options available for these infections are limited; therefore, monitoring, and management of infections due to MRSA with reduced susceptibility to vancomycin, must be done in order to control spread of these strains in the hospital environment. J Microbiol Infect Dis 2014; 4(4): 152-158