Whole-genome profiling reveals mobile genetic elements associated with virulence and antibiotic resistance in equine Lactic Acid Bacteria

Abstract Background While lactic acid bacteria (LAB) are widely recognized as probiotics, their genomic safety remains understudied. Method This study integrates phenotypic characterization, whole genome sequencing (WGS), and horizontal gene transfer (HGT) analysis to evaluate the safety of two LAB strains isolated from healthy equines. Method Phenotypic assays revealed robust acid and bile salt tolerance, antimicrobial activity against pathogens ( Salmonella spp., Escherichia coli ), and α-hemolysis on horse and sheep blood agar. WGS identified multiple antibiotic resistance genes ARGs ( lmrS, optrA, vanTG ) and virulence factors (Adhesion, biofilm formation, immune evasion) in both strains. Crucially, HGT-associated mobile elements (plasmids, genomic islands) were found to carry ARGs ( vanTG, macB ) and virulence genes ( T2SS, InlJ ). For instance, F3d’s plasmid encoded 14 virulence-related genes, while F3c’s genomic island harbored TcdA (Toxin) and patB (Multidrug efflux). These findings demonstrate that mobile genetic elements (MGEs) contribute to the retention of pathogenic traits in LAB, highlighting potential safety concerns. Conclusion This study demonstrate that mobile genetic elements (MGEs) contribute to the retention of pathogenic traits in LAB, highlighting potential safety concerns and underscores the necessity of screening LAB for MGEs to ensure safety in probiotic applications.