Antagonismo de bactérias da microbiota fecal humana contra enteropatógenos

Abstract

The term "indigenous microbiota" refers to the population of micro-organisms normally present on the surface and mucosa of an individual, where performs functions essential to the health of the host, including the colonization resistance (CR) by pathogens. The CR may occur due to the production of antagonistic substances and/or the competition for nutrients and binding sites. To identify the bacteria responsible and the mechanisms involved in the CR, the germ-free (GF) animal model has been used, because in vitro studies cannot always be extrapolated to what occurs in vivo. In the present study, after standardization of the methodology, ex vivo antagonism tests against seven enteropathogenic indicator bacteria using feces from 15 healthy human volunteers, confirmed that the CR showed individual variation, with seven volunteers (46%) having a high CR (six or more indicators inhibited), four subjects (27%) an intermediate CR (four to five indicators inhibited), and four subjects (27%) a low CR (one to two indicators inhibited). Using in vitro antagonism assays and with culture supernatant, 14 strains isolated from fecal dominant microbiota of volunteers with elevated CR were selected for association in GF mice. In the in vivo antagonism assay against Salmonella enterica ser. Typhimurium, mice monoassociated with Enterococcus hirae (8.2), Bacteroides thetaiotaomicron (16.2) and Lactobacillus ruminis (18.1) strains had significant reductions in fecal counts of the pathogen during the challenge. After five days of infection, the 8.2 group showed a reduction (p < 0.05) in the translocation of S. Typhimurium to the spleen, while the 18.1 group had an increased (p < 0.05) translocation to the liver. These results were confirmed by the histological data, in which only the 8.2 group showed clear protective signs of ileum and liver, compared to the damage caused by challenge with S. Typhimurium in a control group, while in group 18.1 there was significantly more intense lesions. Concluding, from the dominant fecal microbiota from healthy human donors having a high CR, and using ex vivo, in vitro and in vivo assays, a bacterium with a high CR potential was selected.