Emergence of staphylococcal cassette chromosome mec type I with high-level mupirocin resistance among methicillin-resistant Staphylococcus aureus

Objective To investigate the molecular epidemiology and antimicrobial resistance patterns of methicillin-resistant Staphylococcus aureus (MRSA) among healthcare workers and patients. Methods MRSA isolates were recovered from nasal swabs collected at a tertiary care hospital of Nepal and confirmed on the basis of Gram staining, conventional biochemical tests, and PCR amplification of mecA gene. PCRs were also used for detection of the different resistance genes and staphylococcal cassette chromosome (SCC) mec types. Antibiotic susceptibility patterns of isolates were assessed by disc diffusion method and minimum inhibitory concentrations were determined by E-test. Results A total of 29 MRSA were isolated from 536 nasal swabs (5.4%) of health care workers and patients at a tertiary care hospital in Nepal. All isolates were susceptible to amikacin, gentamicin, vancomycin (minimal inhibitory concentrations < 2 μg/mL), tigecycline, tetracycline, nitrofurantoin, rifampicin, quinupristin-dalfopristin, and linezolid. Among the 29 MRSA isolates, resistance to erythromycin (72%), ciprofloxacin (75%), co-trimoxazole (62%), clindamycin (10%), and chloramphenicol (10%) was found, and fifteen isolates (51%) exhibited high-level mupirocin resistance (minimal inhibitory concentrations > 1 024 μg/mL). Fourteen isolates were found harboring the mupA gene and one isolate was found carrying the novel mupB gene. High prevalence (68%) of SCC mec I type was found, followed by SCC mec V (13%) and SCC mec III (3%) among all the MRSA isolates. Conclusions We found the emergence of SCC mec type I with high-level mupirocin resistance among MRSA in Nepal. Data also suggest that MRSA SCC mec type V strain has spread from the community to the hospital.