In vitro probiotic characteristics and whole-genome sequencing analysis of porcine-derived lactic acid bacteria
Lactic acid bacteria (LAB) have potential applications as probiotics, but the antibiotic resistance genes (ARGs) and virulence factor genes (VFGs) they carry pose significant public health risks. In this study, eight strains of LAB were isolated from fecal samples of large-scale pig farms, and their probiotic potential and safety were systematically evaluated through in vitro functional assays and whole-genome sequencing. The results showed that Pediococcus pentosaceus R124 exhibited high adhesion to intestinal epithelial cells (54.11%) and strong coaggregation ability (34.9%). Lactiplantibacillus plantarum Z108 demonstrated relatively strong acid resistance (24.18% survival rate at pH 2.0), while Enterococcus faecium F130 showed the highest tolerance to high concentrations of bile salts (6.28%). All strains exhibited a non-hemolytic γ -hemolysis phenotype, but antibiotic susceptibility testing revealed widespread phenotypic multidrug resistance. Interestingly, while P. pentosaceus R124 and L. plantarum Z108 showed resistance to certain antibiotics, genomic analysis indicated they harbored no acquired ARGs or VFGs, suggesting that their observed resistance may stem from intrinsic mechanisms. E. faecium F130 harbored four VFGs and thirteen ARGs, eight of which were located on plasmids. Importantly, the filter-mating experiment indicated that the antibiotic-resistant plasmid PlasmidE and its associated resistance gene ANT(4’)-Ib from E. faecium F130 could be horizontally transferred to recipient strains, conferring antibiotic resistance. This study suggests that, while all isolated strains possess certain probiotic potential, their safety varies according to species and strain-specific characteristics. P. pentosaceus R124 and L. plantarum Z108 are promising candidates with both functional and genetic safety, while the risk of resistance spread from E. faecium F130 highlights the necessity of whole-genome safety assessments in probiotic screening.