Prevalence of vanA, B, C and cfr resistance genes among clinical isolates of Staphylococcus aureus and their role in biofilm formation

Background: The increasement in the resistance to methicillin and the ineffectiveness of beta-lactams among methicillin-resistant Staphylococcus aureus (MRSA) has led vancomycin and linezoli to be as selective drugs for treating Staphylococcal infections, in particular MRSA. The aim of this study was to explore the vancomycin and linezolid resistance in clinical isolates of S. aureus that produce biofilm. Materials and methods: Standard microbiology methods were applied to identify 270 S. aureus isolates. Both were confirmed by the femA gene. Resistance to methicillin and linezolid was investigated by disc diffusion and agar dilution methods, and it was confirmed by E-test and biofilm formation was determined. All isolates were examined for mecA gene for MRSA. Specific primers were used to detect vancomycin (vanA, B, C), and linezolid resistance (cfr gene) and next the PCR products. Results: One-hundred and fifty-two (56.3%) isolates were resistant to methicillin (MRSA) and 6 (1.2%) of them were nonsusceptible to vancomycin and likewise 10 (3.7%) isolates were resistant to linezolid. About 243(90%) isolates of S. aureus were positive for biofilm production. Additionally, 144 isolates (53.3%) were MRSA by mecA gene. The vanA gene was detected in two isolates (0.7%), but none of them has amplified the cfr gene. Conclusion: Resistance to methicillin was high and vancomycin resistance via vanA gene was detected, which enhances the risk of spreading vancomycin resistance. However, resistance to linezolid was not associated with the cfr gene. Therefore, linezolid is yet a valuable antimicrobial in the eradication of S. aureus infections. Our study showed there is an association between Staphylococcus aureus resistance and biofilm production of our isolates.