Occurrence of tetracycline residues in cattle manure from southern Malawi: implications for antimicrobial resistance and One Health

Abstract Antibiotic residues in livestock manure are a recognized environmental driver of antimicrobial resistance (AMR), yet no data exist on residue concentrations in cattle manure from Malawi despite unregulated veterinary drug access, widespread sub-therapeutic dosing, and extensive use of manure as agricultural fertiliser. We conducted a cross-sectional study in Chikwawa and Nsanje districts of southern Malawi to quantify tetracycline-class residues in beef cattle manure by LC-MS/MS, comparing intensive farm (n = 49) and smallholder (n = 41) production systems, with antimicrobial susceptibility patterns of indicator Enterobacteriaceae evaluated to provide contextual evidence for the environmental implications of residue contamination. Fresh manure samples (n = 90) were analysed for tetracycline-class residues and for Enterobacteriaceae AMR by Kirby-Bauer disk diffusion. Chlortetracycline, tetracycline, and doxycycline were detected in all 90 samples; oxytetracycline in 55 (61.1%). Chlortetracycline and tetracycline concentrations were significantly higher in intensive farm samples (Mann-Whitney U test: p = 0.0009 and p < 0.001), consistent with more systematic antibiotic use in commercial production. Indicator Enterobacteriaceae isolates showed universal tetracycline resistance (100%; 95% CI 96.1–100.0%) and near-universal amoxicillin-clavulanic acid resistance (96.7%; 95% CI 90.8–99.3%), alongside low resistance to cefpodoxime (7.6%), ciprofloxacin (5.4%), and trimethoprim-sulphamethoxazole (4.7%), and no gentamicin resistance; isolates resistant to all five tested antibiotics were exclusively from intensive farm samples, though overall multidrug resistance (≥ 3 antimicrobial classes) did not differ significantly between production systems. No significant correlation was detected between residue concentrations and resistance proportions, consistent with resistance already being fixed at the population level rather than driven by contemporaneous residue burden. In exploratory regression modelling, female cattle had significantly higher doxycycline concentrations than males (4.75 vs. 4.30 ppb; p = 0.045). These findings provide the first evidence of widespread tetracycline-class residue contamination in cattle manure from Malawi, co-occurring with highly resistant Enterobacteriaceae, and underscore the One Health risks of applying residue-laden manure to agricultural land, highlighting an urgent need for antimicrobial stewardship policy, veterinary drug regulation, and manure management practice.