Phenotypic and Genotypic Characterization of Methicillin and Erythromycin Resistance in Staphylococcus aureus Collected from Nasal Samples in Qazvin Medical Students

Macrolide, lincosamide and streptogramin B (MLSB) are used in the treatment of staphylococcal infections. The excessive use of these antibiotics has led to the emergence of resistance in this organism. The present study aimed to access phenotypic and genotypic factors involved in resistance to methicillin and erythromycin in S. aureus isolated from nasal samples in students in hospital. This cross sectional study was conducted among 172 students in Qazvin hospitals in 2015. The bacterial isolates were identified by standard laboratory methods. Antibacterial susceptibility and D-test were performed using disk diffusion method. The presence of ermA,􀀃 ermB, ermC, msrA􀀃and􀀃mecA􀀃genes was evaluated by polymerase chain reaction (PCR) method. Among 172 samples, 50 (29%) were S. aureus. In total, 4 (8%) isolates were resistant to erythromycin and clindamycin (cMLSb phenotype), 12 (24%) isolates showed inducible resistance (iMLSb), and 6 (12%) isolates were resistant to erythromycin and susceptible to clindamycin (MS phenotype). Twenty-four (48%), 10 (20%), 12 (24%), 4 (8%), and 6 (12%) isolates were positive for the presence of ermA,􀀃ermB, ermC, msrA􀀃and􀀃mecA􀀃genes, respectively. The findings of this study showed the considerable rate of S. aureus isolates and genes conferring resistance against MLSB antibiotics in nasal samples collected from students. Continuous monitoring and treating of nasal carriers