Metagenomics insights into the effects of lactic acid bacteria inoculation on the microbial communities and antibiotic resistance genes in mare milk.

Antibiotic resistance genes (ARGs) are emerging contaminants threatening public health, yet their transmission risk via mare milk products remains understudied. Using metagenomics, we analyzed lactic acid bacteria (LAB)-inoculated fermented, naturally fermented, raw, and pasteurized mare milk to investigate the effect of LAB inoculation on the distribution and transmission pathways of ARGs in mare milk. The results showed that naturally fermented, raw, and pasteurized mare milk had the highest number of pathogens, relative abundance of ARGs, and relative abundance of mobile genetic elements (MGEs), while LAB inoculation significantly reduced these (p < 0.05). Bacillota was the dominant microbial group in different samples. Compared to naturally fermented and raw mare milk, LAB-inoculated fermentation significantly altered microbial community structure (p < 0.05). This not only reduced or eliminated certain harmful bacteria but also decreased the abundance of total ARGs and multiple ARG subtypes by reducing host bacteria and MGEs. Microbes and MGEs jointly drove ARG transmission, with microbes being key. Transposon, Bacteroidota, and Pseudomonadota are the major MGEs and microbial taxa for ARG transmission. LAB inoculation can effectively inhibit the spread of 11 ARG types, including β-lactam and multidrug resistance, by weakening the co-occurrence network among microbes, ARGs, and MGEs. This study enhances understanding of resistance genes in diverse equine dairy products, elucidates the impact of LAB fermentation on ARG distribution and transmission pathways in mare milk, and provides valuable data references and theoretical guidance for safer equine dairy processing.