In vivo assessment of potential probiotic Lactobacillus salivarius strains: Evaluation of their establishment, persistence, and localisation in the murine gastrointestinal tract

The enteric flora comprise approximately 95% of the total number of cells in the human body, Numerous studies have investigated potentially beneficial members of this microbial community due to their ability to elicit immune responses while also protecting against microbial pathogens. We have previously reported on the isolation and identification, from surgically- resected segments of the human gastrointestinal tract (GIT), of potential probiotic lactic acid bacteria (LAB). These bacterial strains exhibit potentially beneficial probiotic traits in vitro such as bile tolerance in the absence of deconjugation; gastric acid resistance; and adherence to epithelial cell lines. The objective of this study was to administer two strains of the previously-isolated LAB to mice over a period of 7 or 14 days in order to assess their ability to establish themselves within specific regions of the GIT. Throughout this feeding period, and for 4 days following cessation of feeding, the numbers of total culturable lactobacilli and of the administered LAB present in faeces were monitored. Spontaneous rifampicin resistant derivatives (50 μg/ml) of Lactobacillus salivarius subsp. salivarius UCCI(LM5) and Lb. salivarius subsp. salivarius UCC118(LM2) were generated to facilitate enumeration of the strains in GIT and faecal samples. Each potential probiotic strain was individually administered to Balb/c mice at a daily concentration of approximately 4.0 x 10⁹ CFU. After 1 day of feeding, strains UCCI(LM5) and UCC118(LM2) were recovered from murine faeces at Log₁₀ 6.95 (1.18) CFU/g and Log₁₀ 6,33 (0.37) CFU/g, respectively. Interestingly, UCC118(LM2), which was originally isolated from the ileal- caecal region of the human GIT, was found to have become established in the corresponding region of the murine GIT regardless of the length of the feeding period, UCC118(LM2) was also found to persist in faeces for a period of up to 3 days following cessation of feeding. Administration of UCCI(LM5) and UCC118(LM2) did not result in any significant changes in the levels of indigenous bacteria culturable from faeces. In conclusion, human isolate Lb. salivarius subsp, salivarius UCC118(LM2) was found to effectively colonise, and survive transit through, the murine gastrointestinal tract. Lactobacillus salivarius subsp. salivarius UCC118 has been deposited at The National Collections of Industrial and Marine Bacteria (NCIMB) and accorded the accession number NCIMB40829.