Identification of Antibiotic-Resistant Bacteria in Effluent Discharged from the Pharmaceutical Industry in Ogun State

The release of pharmaceutical effluents containing sublethal antibiotic concentrations into aquatic environments is increasingly recognized as a driver of environmental antibiotic resistance. This study characterized antibiotic-resistant bacteria present in effluents discharged from two pharmaceutical manufacturing facilities in Ogun State, South West Nigeria. Effluent samples were collected from discharge points and adjacent water bodies over a 12-week period. Bacterial isolation was conducted on nutrient agar and selective media. Antibiotic susceptibility testing using disk diffusion and minimum inhibitory concentration (MIC) determination by broth microdilution was performed for 12 antibiotics across five drug classes. Integron screening by PCR was used to assess the genetic basis of resistance in selected isolates. A total of 120 bacterial isolates were recovered, with Pseudomonas aeruginosa (31%), E. coli (26%), Klebsiella pneumoniae (19%), and Acinetobacter baumannii (14%) predominating. Multi-drug resistance was observed in 78 percent of all isolates, and class 1 integrons were detected in 46 percent. Extended-spectrum beta-lactamase (ESBL) producers were identified among 35 percent of Enterobacteriaceae. These findings establish pharmaceutical effluent in Ogun State as a significant reservoir of multi-drug-resistant bacteria and resistance genes. The study recommends mandatory effluent treatment and resistance monitoring as part of environmental pharmaceutical stewardship. Keywords: pharmaceutical effluent, antibiotic resistance, multi-drug resistance, ESBL, Ogun State.