Enterobacteria in anaerobic digestion of dairy cattle wastewater: Assessing virulence and resistance for one health security

•Physicochemical analysis revealed stable anaerobic digestion in varying seasons.•Total bacteria and coliform counts decreased significantly during anaerobic digestion.•Biofilm-forming capacity was observed in a majority of isolated strains.•Seasonal variations affected antimicrobial resistance in isolated strains.•Biofertilizers harbored multidrug-resistant strains, posing potential risks to public health. Samples from a dairy cattle waste-fed anaerobic digester were collected across seasons to assess sanitary safety for biofertilizer use. Isolated enterobacteria (suggestive of Escherichia coli) were tested for susceptibility to biocides, antimicrobials, and biofilm-forming capability. Results revealed a decrease in total bacteria, coliforms, and enterobacteria in biofertilizer compared to the effluent. Among 488 isolates, 98.12 % exhibited high biofilm formation. Biofertilizer isolates exhibited a similar biofilm formation capability as effluent isolates in summer, but greater propensity in winter. Resistance to biocides and antimicrobials varied, with tetracycline resistance reaching 19 %. Of the isolates, 25 were multidrug-resistant (MDR), with 64 % resistant to three drugs. Positive correlations were observed between MDR and increased biofilm formation capacity in both samples, while there was negative correlation between MDR and increased biocide resistance. A higher number of MDR bacteria were found in biofertilizer compared to the effluent, revealing the persistence of E. coli resistance, posing challenges to food safety and public health. [Display omitted]