Abstract: In this study, 23 strains of Bifidobacterium longum subsp. infantis were isolated and identified from 150 infant fecal samples in Northwest China by a culture method combined with polymerase chain reaction, with an isolation rate of only 10.67%. The genomes and probiotic properties of these strains of B. infantis were compared and analyzed. Genomic analysis showed that the average GC content, genome size, and number of coding sequences of B. infantis were 59.81%, 2.61 Mb, and 2 273, respectively. Phylogenetic analysis based on core genes and average nucleotide identity (ANI) analysis showed that strains from the same geographical origin had high genetic similarity and close phylogenic relationships. There were differences in gene families related to plant-derived carbohydrate metabolism among strains. Carbohydrate metabolism experiments showed that most B. infantis strains were able to metabolize prebiotics such as galactooligosaccharides, oligofructose, and inulin, corroborating the presence of the glycoside hydrolase (GH) 32 and GH43 gene families, and four strains (A47X1, A79X4, A79X3, and S19X4) were able to utilize xylose. B. infantis S8X8 and S5X8_2 most effectively inhibited diarrheagenic Escherichia coli CICC-10411, enterotoxigenic E. coli CICC-10421, Salmonella enterica subsp. enterica serovar Typhimurium CICC-10420, enterohaemorrhagic E. coli CICC-21530, S. enterica subsp. enterica serovar Enteritidi CGMCC1.10754-SM1, but did not inhibit Listeria monocytogenes CGMCC1.9136-LS1. Intrinsic resistance genes to antibiotics such as rifampicin, mupirocin, and aminoglycoside, but not pathogenic virulence factors, were detected in the genome of B. infantis. All B. infantis strains were susceptible to vancomycin, gentamicin and streptomycin. This study provides a reference for the development of personalized probiotic preparations for infants in different regions.

Key words: Bifidobacterium longum subsp. infantis; comparative genomics; probiotic properties