Genomic evaluation of the probiotic and pathogenic features of Enterococcus faecalis from human breast milk and comparison with the isolates from animal milk and clinical specimens.

Enterococcus faecalis is considered a probiotic, commensal lactic acid bacterium in human breast milk (HBM), but there are circulating antibiotic resistant and virulence determinants that could pose a risk in some strains. The study aimed to conduct genomic analysis of E. faecalis isolates recovered from HBM and animal milk and to evaluate their probiotic and pathogenic features through comparative genomics with isolates from clinical specimens (e.g., urine, wound, and blood). Genomic analysis of 61 isolates was performed, including E. faecalis isolates recovered from HBM in Saudi Arabia. Genome sequencing was conducted using the MiSeq system. The fewest antibiotic resistance genes (lsaA, tetM, ermB) were identified in isolates from HBM and animal milk compared to clinical isolates. Several known and unknown mutations in the gyrA and parC genes were observed in clinical isolates. However, 11 virulence genes were commonly found in more than 95% of isolates, and 13 virulence genes were consistently present in the HBM isolates. Phylogenetically, the HBM isolates from China clustered with the probiotic reference strain Symbioflor 1, but all isolates from HBM and animal milk clustered separately from the clinical reference strain V583. Subsystem functions 188 of 263 were common in all analyzed genome assemblies. Regardless of the source of isolation, genes associated with carbohydrate metabolism, fatty acid, and vitamin biosynthesis were commonly found in E. faecalis isolates. In conclusion, comparative genomic analysis can help distinguish the probiotic or pathogenic potential of E. faecalis based on genomic features.