Daptomycin Resistance among Methicillin Resistant Staphylococcus aureus Strains

Methicillin-resistant Staphylococcus aureus (MRSA) has a great potential to acquire resistance to antimicrobial agents, which made treating of infections much more challenging. The aim of this study was to determine the daptomycin resistance of MRSA strains isolated from catheterized patients with urinary tract infection (UTI) in Tehran during 3 years. A total of 419 S. aureus strains isolated from patients were identified using specific primers. MRSA strains were also detected using cefoxitin disk and specific primers for mecA gene; and minimum inhibitory concentration (MIC) of oxacillin was also determined. Moreover, the presence of different types of SCCmec and ccr types were also showed. All MRSA strains were also tested for susceptibility to daptomycin by disk diffusion method. One hundred and eight cefoxitin resistant and mecA positive S. aureus strains were detected among isolates in which 97% harbored SCCmec type III and were positive for type 3 ccr. On the other hand, SCCmec type IVa and type 2 ccr were also detected in 3% of MRSA strains. Moreover, among MRSA strains 56% showed resistance to ≥256 μg/ml oxacillin and using disk diffusion method, 86% of MRSA strains were also resistant to daptomycin. The results of this revealed that daptomycin is not a drug of choice for treatment of patients with UTI in this hospital.