Characterization of the anti-pathogenic, genomic and phenotypic properties of a Lacticaseibacillus rhamnosus VHProbi M14 isolate

A strain of lactic acid bacteria from cheese was isolated, that showed strong growth inhibitory effects on Streptococcus mutans. The API 50CH system and 16S rDNA sequencing verified that this was a novel strain, and was named Lacticaseibacillus rhamnosus VHProbi M14. The strain inhibited the growth of S. mutans and Fusobacterium nucleatum under mixed culture conditions, coaggregated with S. mutans and F. nucleatum, and reduced the adhesion of S. mutans and F. nucleatum on cultured human primary gingival epithelial (HPGE) cells. The pH, peroxidase and protease sensitivity testing found antibacterial substances of protein- and peptide-like structures in addition to organic acids. The antimicrobial substances were sensitive to hydrolysis with trypsin, papain and pineapple protease and were inactived at temperatures above 100°C. Ammonium sulphate-precipitated proteins from the M14 strain retained the ability to inhibit the growth of S. mutans and F. nucleatum. The M14 strain contained 23 bacteriocin-related genes encoding for metabolites, belonging to class II bacteriocins. The M14 strain also showed inhibitory effects on 8 other pathogenic strains (A. actinomycetemcomitans, C. albicans, E. coli, G. vaginalis, P. acnes, P. gingivalis, S. aureus, S. enteritids), and thus has a broad spectrum of bacterial inhibition. This new isolate has been identified as having potential to be used as a probiotic bacterium in clinical applications.