Abstract
The development and spread of superbugs, which are bacterial strains resistant to several types of antibiotics, threatening the lives of myriad people and animals worldwide, is one of the most concerning issues facing both global and animal health. Dairy animals are considered to be key reservoirs of antibiotic-resistant bacteria, which are closely correlated with the widespread and inappropriate application of antibiotics in agriculture and veterinary medicine, particularly for mastitis treatment. Although antimicrobial agents are administered in dairy farming for various conditions beyond mastitis, such as respiratory infections and digestive disorders, as well as prophylaxis and growth promotion, the most common reason for antimicrobial use in this industry is mastitis treatment. Since raw milk can be contaminated with opportunistic pathogens carrying antimicrobial resistance genes, these pathogens increase the gene pool from which pathogenic bacteria can acquire resistance traits. Indeed, these resistance genes may be horizontally transferred from livestock to human pathogens through mobile genetic elements through the consumption of raw milk. This phenomenon poses a global health threat, emphasizing the necessity of applying the “One Health” approach in global health and medicine to safeguard animal health and public health. Given the high prevalence and economic impact of mastitis and the evidence supporting mastitis as a major driver of antimicrobial use in dairy farming, this review summarizes recent genomic and metagenomic studies on major mastitis-causing pathogens (Staphylococcus aureus, Escherichia coli, Streptococcus spp., and Pseudomonas spp.) in dairy animals, detailing their primary resistance mechanisms. We highlight advanced surveillance tools, such as metagenomics, whole-genome sequencing, and quantitative polymerase chain reaction, for the rapid detection of resistance genes and mobile elements in the dairy chain.

Key words: Antimicrobial resistance; Mastitis; Opportunistic pathogens; Resistance genes; Veterinary.