Abstract

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 sus¬ceptibility 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 re¬maining 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 iso¬lates 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

Key words: Staphylococcus aureus, methicillin resistance, MIC, virulence factor, biofilm. Mohammad Reza Shakibaie, Yasser Golkari, Gholamabas Salajegheh. Antimicrobial susceptibility, virulence factors and biofilm formation among Staphylococcus aureus strains from hospital infections in Kerman, Iran. J Microbiol Infect Dis 2014; 4(4): 152-158 doi: 10.5799/ahinjs.02.2014.04.0159