Methods: As part of a longitudinal study (total n=240) on infant growth and development of infant formula, saliva samples and oral swabs were collected from 133 infants. Saliva was cultured and Lactobacillus isolates were identified from 16S rRNA gene sequences. Oral swabs were analyzed by qPCR for Lactobacillus gasseri. Five L. gasseri isolates that differed in 16S rRNA sequences were tested in vitro for growth inhibition and adhesion.
Results: Of infants sampled, 43 (32.3%) were breastfed and 90 (67.7%) were formula-fed with either a standard formula (43 out of 90) or a similar formula supplemented with Milk Fat Globule Membrane fraction (MFGM). Lactobacilli were detected in saliva from 29.3% of breastfed infants, but only in 4.7% and 9.3% of the standard and MFGM supplemented formula-fed infants, respectively. L. gasseri was the most prevalent (88% of Lactobacillus positive infants) of six Lactobacillus species detected. L. gasseri was detected in 30.2% of the oral swabs using qPCR, including 44% mucosal swab samples that were positive for Lactobacillus species by saliva culture. L. gasseri inhibited Streptoccoccus mutans binding to saliva-coated hydroxyapatite and growth of S. mutans, Streptoccoccus sobrinus, Actinomyces naeslundii, Candida albicans and Fusobacterium nucleatum in a concentration dependent fashion. L. gasseri bound to saliva, saliva gp340, and purified MFGM, and adhered to the human epithelial KB cell line.
Conclusions: We conclude that lactobacilli are present in saliva of 30% of 4 month-old breastfed infants, with dominance of L. gasseri, which displays characteristics consistent with probiotic traits in vitro.