A recent study from the French National Institute for Agricultural Research (INRA), led by Dr. Patrick Veiga from the Danone Nutricia Research scientific team, has brought new insights regarding the role of exogenous bacteria administered by a fermented milk product on the ecological robustness of the gut microbiota in rats.
One function of the resident gut microbiota is preventing colonization by pathogenic exogenous bacteria (termed as ‘colonization resistance’ or ‘the barrier effect’). The researchers examined if the host’s resident gut microbiota influences colonization resistance for beneficial bacteria administered in a fermented milk product (FMP) containing five strains: Bifidobacterium animalis subsp. lactis CNCM I-2494, Lactococcus lactis subsp. lactis CNCM I-1631, Lactobacillus delbrueckii subsp. bulgaricus CNCM I-1632, L. delbrueckii subsp. bulgaricus CNCM I-1519 and Streptococcus thermophilus CNCM I-1630.
The elimination kinetics of the FMP bacterial species varied across rats (n = 24). During the FMP intervention, L. lactis CNCM I-1631, B. lactis CNCM I-2494, L. bulgaricus CNCM I-1632 and L. bulgaricus CNCM I-1519 were detected and quantified in 100% of the stool samples, whereas S. thermophilus was only poorly recovered in the stool and thus it was not investigated further. The transient persistence of the L. lactis strain differed between individual rats. One subgroup of rats (termed ‘resistant’) eliminated L. lactis CNCM I-1631 in a time that kept pace with normal gastrointestinal transit, whereas a second subgroup of rats (called ‘permissive’, n = 12) shed the strain in their stool over 2 additional days. The latter rats, therefore, had a gut microbial community that allowed the food-borne bacteria to persist longer.
Gut microbiota analyses showed that both resistant and permissive rats differed in their gut microbiota and in the amplitude of ecological changes induced by the FMP. Permissive rats had a higher relative abundance of Ruminococcaceae, and a lower relative abundance of Lachnospiraceae, compared with resistant rats, whereas resistant rats had a gut microbiota less susceptible to FMP-induced changes. The researchers observed similar patterns to a previous study that investigated the effects of a similar FMP on human gut microbiota (n = 14). Besides this, the variation of the gut microbiota induced by the FMP intervention was higher in permissive rats than in resistant ones, which points to an ecological robustness of the gut microbiota in resistant rats. All together, these results suggest that permissivity to L. lactis is associated with a specific gut microbiota structure.
Finally, the transfer of faecal microbiota from permissive and resistant donors into germ-free rats demonstrated that colonization resistance for L. lactis CNCM I-1631 was gut microbiota-dependent.
In conclusion, resistant rats, as assessed by clearance of L. lactis following FMP intervention, have a more robust gut microbiota compared with permissive rats. Therefore, bacteria in foodstuffs like fermented milk may have transient and individual effects on the gut microbiota. This suggests close interactions between resident and transient bacterial communities. More research is necessary to determine whether these findings apply to humans consuming probiotic food products with characterized strains.
Zhang C, Derrien M, Levenez F, et al. Ecological robustness of the gut microbiota in response to ingestion of transient food-borne microbes. ISME J. 2016. doi:10.1038/ismej.2016.13.