2016 Volume 4 Issue 1 Pages 28-34
Introduction: The relationships among the virulence of methicillin-resistant Staphylococcus aureus (MRSA) strains, their antibiotic susceptibility, and the presence of enterotoxin genes have been frequently discussed. The differences between hospital-associated (HA) and community-associated (CA) MRSA strains isolated from the otorrhea of patients with chronic otitis media (COM) were examined to determine which factors influence the prognosis of MRSA-associated COM.
Materials and Methods: Our study included five strains of both clonal complex (CC) 5 HA-MRSA and CC 8 CA-MRSA as determined by phylogenetic analysis using multilocus sequence typing. The minimum inhibitory concentrations (MICs) of anti-MRSA antibiotics and the presence of toxigenic genes were investigated using the E-test® and Multiplex PCR, respectively. Antibiotic susceptibilities were obtained from chart reviews, and MIC antibiotic breakpoints were evaluated.
Results: The MIC of vancomycin was >1.5 μg/ml in all strains. The MIC of linezolid was 0.5 to 0.75 μg/ml for the HA-MRSA strains and 2 to 6 μg/ml for the CA-MRSA strains. The MIC of clindamycin was 256 μg/ml for all HA-MRSA strains, 256 μg/ml for a single CA-MRSA strain, and 0.064 to 0.084 μg/ml for the remaining four CA-MRSA strains. The MIC of minocycline was 6 to 12 μg/ml in all HA-MRSA strains and 0.064 to 0.094 μg/ml in all CA-MRSA strains. There were no differences in the MIC of teicoplanin, daptomycin, sulfamethoxazole/trimethoprim, or rifampicin between the HA- and CA-MRSA strains.
Five to 7 of a total 17 Staphylococcus aureus enterotoxin genes were identified in the HA-MRSA strains. The tsst-1 gene had a prevalence of 40% among the HA-MRSA strains. No toxigenic genes were identified in the CA-MRSA strains. The Panton-Valentine leukocidin gene was not identified in any strains.
The following differences in antibiotic susceptibility between the HA- and CA-MRSA strains were identified: cefazolin (0% vs. 60%, respectively), flomoxef (60% vs. 100%), cefozopran (60% vs. 100%), meropenem (0% vs. 60%), clindamycin (0% vs. 80%), gentamycin (20% vs. 80%), minocycline (60% vs. 100%), and fosfomycin (20% vs. 100%).
Conclusions: The MIC of vancomycin was high for both HA- and CA-MRSA strains, and the MIC of linezolid was higher in CA-MRSA strains. More toxigenic genes were identified in HA-MRSA strains than in CA-MRSA strains. In the clinical setting, antibiotic susceptibilities based on chart reviews may help to identify which course of treatment to pursue for different MRSA strains.
