Comparative analysis of antimicrobial resistance in Nile tilapia from polluted natural waters versus aquaculture systems in Zimbabwe: Public health and sustainable aquaculture implications

Antimicrobial resistance (AMR) is an escalating global health crisis, particularly in aquaculture, where environmental contamination contributes to the proliferation of resistant pathogens. This study examines AMR patterns and antimicrobial residue levels in Nile tilapia from natural water bodies and aquaculture ponds in Zimbabwe. Six hundred fish samples were collected from four lakes and six aquaculture ponds and analysed by bacterial isolation using API kits, antibiotic susceptibility testing via disk diffusion, and residue analysis using Charm II assays. Results showed significantly higher AMR levels and antimicrobial residues in fish from polluted waters, particularly Lake Chivero, compared to aquaculture ponds. Notably, Escherichia coli demonstrated 100% resistance to penicillin, while Bacillus spp exhibited intrinsic resistance to penicillin and carbapenems. Imipenem resistance reached 96% in E. coli. β-lactam residues were detected in 72.5% of Lake Chivero fish, compared to 5% in aquaculture ponds. Additionally, sulfa drugs (81.67%) and streptomycin (43.33%) were also prevalent in polluted waters, correlating with the observed resistance patterns. In contrast, fish from aquaculture ponds exhibited significantly lower resistance and residue levels, reflecting improved management practices. The findings emphasise the role of environmental pollution and anthropogenic activities in driving acquired AMR in aquatic ecosystems. They highlight the urgent need for stricter wastewater management, sustainable aquaculture practices, and robust antimicrobial stewardship policies. Future research should focus on non-antibiotic pathogen control strategies, metagenomic analysis of resistance gene flow, and the socio-economic impacts of AMR to mitigate its growing threat to public health and aquatic environments.