Genomic Insights Into Antimicrobial Resistance and Virulence of <i>Enterococcus avium</i> Strains From Bovine Mastitis in Some Selected Dairy Farms of Bangladesh

BACKGROUND: Bovine mastitis remains a major global threat to dairy production and animal welfare, with the increasing emergence of multidrug-resistant (MDR) pathogens severely undermining the efficacy of conventional antimicrobial therapies and complicating disease control strategies. Enterococcus avium, traditionally understudied in livestock, has been occasionally associated with mastitis and poses potential zoonotic and antimicrobial resistance (AMR) risks. OBJECTIVES: This study aimed to investigate the prevalence, AMR, virulence repertoire and genomic features of E. avium isolates from milk, faeces and soil in some selected dairy farms with mastitis in Bangladesh. METHODS: A total of 110 samples (milk, faecal and soil) were collected and screened for E. avium using selective culture and polymerase chain reaction (PCR). Antimicrobial susceptibility was determined against 15 antibiotics. Four MDR E. avium isolates (4M1, 4S1, 4F1 and 4F2) were selected for whole-genome sequencing (WGS) to characterize their genomic diversity, functional potential, resistome and virulome in dairy cows and associated environments. RESULTS: E. avium was detected in 56.36% of samples, with highest prevalence in milk (47.8%). MDR was highly prevalent (93.5%), with frequent resistance to sulphonamides, nitrofurantoin and oxacillin, whereas gentamicin retained activity. Genomic analyses revealed conserved core genomes alongside variable accessory elements, indicating both evolutionary stability and adaptive potential. Phylogenetic proximity to human-derived strains highlights zoonotic risk. Functional profiling demonstrated robust metabolism, environmental sensing, adhesion-related virulence factors and multiple bacteriocin clusters, supporting persistence and microbial competition. ARGs conferring multidrug efflux, β-lactam and fluoroquinolone resistance were conserved across isolates. CONCLUSIONS: E. avium is a prevalent mastitis pathogen, highly conserved among the studied isolates, with significant virulence and AMR profiles, highlighting its zoonotic potential and need for One Health-based surveillance strategies.