Antibiotic Resistance pattern of Methicillin-Resistant Staphylococcus aureus (MRSA) from Selected Pharmaceutical Company Effluents in Ogun State, Nigeria

Background: Pharmaceutical manufacturing effluents have emerged as significant environmental reservoirs of antibiotic-resistant bacteria, posing serious public health threats. Methicillin-resistant Staphylococcus aureus (MRSA) is a major healthcare-associated pathogen, and its presence in industrial wastewater represents a critical pathway for environmental dissemination of resistance determinants. This study investigated the antibiotic resistance patterns of MRSA isolated from wastewater effluents of selected pharmaceutical companies in Ogun State, Nigeria. Objective: To determine the phenotypic antibiotic resistance profiles of MRSA isolates from pharmaceutical company effluents. Methods: A total of 164 Staphylococcus aureus isolates were recovered from pretreated wastewater samples collected from three pharmaceutical companies (A, B, and C) in Ogun State, Nigeria. MRSA was phenotypically identified using cefoxitin disk diffusion (30 µg) according to CLSI guidelines. Antibiotic susceptibility testing was performed using the Kirby-Bauer disk diffusion method against 10 antibiotics from multiple classes, including β-lactams, glycopeptides, aminoglycosides, fluoroquinolones, and lincosamides. Results: The overall MRSA prevalence among S. aureus isolates was 35 (49.3%) in Pharma A, 29 (48.3%) in Pharma B, and 15 (45.5%) in Pharma C. Alarmingly, all MRSA isolates (100%) exhibited resistance to aztreonam, cefoxitin, clindamycin, ceftriaxone, imipenem, trimethoprim-sulfamethoxazole, and vancomycin. High resistance rates were also observed for gentamicin (55.2-71.4%), ofloxacin (72.4-80.0%), and levofloxacin (85.7-86.7%). Conclusion: This study reveals an alarmingly high prevalence of multidrug-resistant MRSA in pharmaceutical wastewater, including complete resistance to vancomycin, a last-resort antibiotic. These findings highlight pharmaceutical effluents as critical hotspots for the environmental dissemination of highly resistant MRSA strains, necessitating urgent regulatory interventions and enhanced wastewater treatment protocols.