Environmental bovine subclinical mastitis gram-negative pathogens: Prevalence, antimicrobial resistance with special reference to extended-spectrum β-lactamases and carbapenemase production

This study investigates mastitis in the dairy industry, with a focus on the issue of antibiotic resistance. This study was designed to evaluate mastitis prevalence and investigate the bacteriological profiles of subclinical mastitis (SCM) milk, mastitis-free milk, and market milk. Out of 374 quarter milk samples, 26.2 % were from animals with SCM. Bacteriological examination identified 87 Gram-negative bacterial strains from subclinical mastitis milk (SCMM) (42.9 %), subclinical mastitis-free milk (SCMFM) (17.97 %), and market milk (MM) (58 %). MALDI-TOF MS identified species including E. coli, K. pneumoniae, Enterobacter cloacae, Citrobacter freundii, Serratia marcescens, and Acinetobacter baumannii, with E. coli being the most frequent. Multi-drug resistant (MDR) phenotype was found in 43.7 % of isolates, with 57.1 % from SCMM, 43.8 % from SCMFM, and 24.1 % from MM. Biofilm production was observed in 44.8 % of isolates, with a significant correlation between MDR and biofilm formation. Eight strains (9.2 %) were extended-spectrum beta-lactamases (ESBLs) producers, with blaCTX-M, blaTEM, and blaSHV genes detected. A. baumannii harbored multiple resistance genes, including blaTEM, blaCTX-M, blaOXA51, blaOXA23, and blaNDM, showing both phenotypic and genotypic ESBLs and carbapenemase activity. The presence of MDR, ESBLs, and carbapenemase producing Gram-negative bacteria in SCMM, SCMFM, and MM indicates a concerning exchange of bacteria and antimicrobial resistance genes between human and animal hosts, posing risks of milk contamination and environmental hazards. A one-health approach is essential for controlling antimicrobial-resistant bacteria, emphasizing prudent antimicrobial use in human and animal healthcare, and improving farm hygiene practices.