Antagonistic substances produced by microorganisms are important to maintenance of the resident microbiota in different ecological niches. They also are used to prevent the exogenous bacterial colonization and invasion, and consequently the development of infectious diseases. In this study, the presence of bacteriocin-producing Bacteroides and Parabacteroides species isolates from human intestinal microbiota was determined by phenotypic assays. Sixty-three (55.2%) out of the 114 strains produced antagonic substances. Our results showed that Bacteroides and Parabacteroides species evaluated produced substances with hetero- or iso-antagonism effects. The iso-antagonistic effect was observed in B. fragilis (40.9%), B. vulgatus (50%) and B. uniformis (14.2%). The production of bacteriocins with both hetero- and iso-antagonic effects may suggest a defense against the invasion of exogenous microorganisms in the intestinal microbiota.
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