TAXONOMIC LACTOBACILLUS COMPOSITION OF FECES FROM HUMAN NEWBORNS DURING THE FIRST FEW DAYS

Intestinal microbiota comprise a complex ecosystem whose equilibrium i s crucial for the health of animal species. For humans, data exist on the microbiota composition in adult subjects, but few studies have add ressed the microbiota composition in infants. In particular, data on t he presence and species distribution of members of the genus Lactobaci llus in newborns (less than one week old) are lacking. In the present work, the feces of healthy newborns were sampled to determine the taxo nomic composition of Lactobacillus in the intestinal microbiota in a g roup of 16 neonates. In total, 1640 colony-forming units (CFU) were is olated, of which 420 grouped in the Lactobacillus genus by means of pr imary phenotypic characterization. The 420 isolates were further group ed into 125 strains on the basis of identical plasmid profiles. Of the se 125 strains, 21 turned out to be permanent, i.e., they were identif ied in the feces of the same subject on several consecutive days. Suga r fermentation, DNA/DNA hybridization, and S-layer protein determinati on enabled us to classify 52 of the 125 strains as follows: L. paracas ei (40 strains), L. delbrueckii sp. (1 strain), and L. acidophilus (se nsu stricto) (11 strains). Based on the same criteria, the remaining 7 3 strains were tentatively allotted to the Johnson subgroup B, althoug h hybridization experiments with probes specific for L. gasseri and L. johnsonii species were not performed. The presence of ne iv species a mong these 73 strains cannot be excluded. Surprisingly, the obligately heterofermentative lactobacilli, L. reuteri in particular, were entir ely absent from the feces of healthy newborns.