Molecular Characterisation of Methicillin-resistant Staphylococcus aureus (MRSA) Isolated from Hospitalised Patients in Public Tertiary Hospitals in Enugu, Nigeria: A Multi-centre Study

Background: Staphylococcus aureus is a major healthcare-associated pathogen and an important cause of morbidity among hospitalised patients. In Nigeria, data on multidrug-resistant S. aureus in clinical settings remain limited. This study characterised methicillin-resistant S. aureus (MRSA) recovered from hospitalised patients in three public tertiary hospitals in Enugu, Nigeria, determined antimicrobial resistance patterns, assessed multiple antibiotic resistance (MAR) indices, and detected the mecA gene. Methods: A prospective cross-sectional multicentre study was conducted between March 2019 and June 2021. A total of 460 clinical samples, including wound/pus swabs, blood cultures, catheter urine, catheter tips and bone tissue, were cultured on mannitol salt agar and blood agar. Presumptive isolates were identified using standard microbiological methods and confirmed with a Staph latex agglutination kit. Antimicrobial susceptibility testing was performed using the modified Kirby-Bauer disc diffusion method, while PCR was used to detect mecA. Results: Fifty-one (11.09%) S. aureus isolates were confirmed, of which 41 (80.39%) were phenotypically identified as MRSA. MRSA isolates showed resistance to cefoxitin (100%), penicillin (97.56%), ciprofloxacin (87.81%), trimethoprim-sulphamethoxazole (82.93%), erythromycin (80.49%), tetracycline (73.17%), gentamicin (63.42%) and cefuroxime (48.78%). Lower resistance was observed to imipenem (2.44%), vancomycin (12.20%), linezolid (26.83%) and clindamycin (29.27%). The MAR index ranged from 0.08 to 0.83, and 48 (94%) S. aureus isolates exceeded the acceptable threshold of 0.2. The mecA gene was detected in 26 (63.41%) MRSA isolates. Conclusion: The findings indicate a high occurrence of multidrug-resistant MRSA among S. aureus isolates from hospitalised patients in Enugu. Continued molecular surveillance, antimicrobial stewardship and infection prevention and control measures are required to support appropriate therapy and limit the spread of resistant strains.