Ethnic Specificity of Species and Strain Composition of Lactobacillus Populations From Mother–Infant Pairs, Uncovered by Multilocus Sequence Typing

The maternal gut is thought to be the principal source of potential probiotic bacteria in the infant gut during the lactation stage. It is not clear whether facultative symbiont lactobacilli strictly follow vertical transmission from mother to infant and display the ethnic specificity in terms of species and strain composition in mother–infant cohorts. In the present study, a total of 16 former Lactobacillus species (365 strains) and 11 species (280 strains) were retrieved from 31 healthy mother–infant pairs of two ethnic groups, which have never intermarried, respectively. The result showed that the composition and number of Lactobacillus species between the two ethnic groups varied. Among 106 Lacticaseibacillus paracasei strains isolated, 64 representative strains were classified into 27 sequence types (ST) by means of multilocus sequence typing (MLST), of which 20 STs derived from 33 Uighur strains and 7 STs from 31 Li strains, and no homologous recombination event of genes was detected between strains of different ethnic groups. A go-EBURST analysis revealed that except for a few mother–infant pairs in which more than one STs were detected, L. paracasei isolates from the same mother–infant pair were found to be monophyletic in most cases, confirming vertical transfer of Lactobacillus at the strain level. More notably, L. paracasei isolates from the same ethnic group were more likely than strains from another to be incorporated into a specific phylogenetic clade or clonal complex (CC) with similar metabolic profile of glycan, supporting the hypothesis of ethnic specificity to a large degree. Our study provides evidence for the development of personalized probiotic tailored to very homogenous localized populations from the perspective of maternal and child health.