Effects of Lactococcus lactis on composition of intestinal microbiota: role of nisin

Abstract

This study examined the ability of (i) pure nisin, (ii) nisin-producing Lactococcus lactis strain CHCC5826, and (iii) the non-nisin-producing L. lactis strain CHCH2862 to affect the composition of the intestinal microbiota of human flora-associated rats. The presence of both the nisin-producing and the non-nisin-producing L. lactis strains significantly increased the number of Bifidobacterium cells in fecal samples during the first 8 days but decreased the number of enterococci/streptococci in duodenum, ileum, cecum, and colon samples as detected by selective cultivation. No significant changes in the rat fecal microbiota were observed after dosage with nisin. Pearson cluster analysis of denaturing gradient gel electrophoresis profiles of the 16S rRNA genes present in the fecal microbial population revealed that the microbiota of animals dosed with either of the two L. lactis strains were different from that of control animals dosed with saline. However, profiles of the microbiota from animals dosed with nisin did not differ from the controls. The concentrations of nisin estimated by competitive enzyme-linked immunosorbent assay (ELISA) were approximately 10-fold higher in the small intestine and 200-fold higher in feces than the corresponding concentrations estimated by a biological assay. This indicates that nisin was degraded or inactivated in the gastrointestinal tract, since fragments of this bacteriocin are detected by ELISA while an intact molecule is needed to retain biological activity.

FIG. 1.

(A) Bifidobacterial populations in feces of rats dosed with nisin-producing L. lactis (closed triangles), non-nisin-producing L. lactis (closed squares), 60 mg nisin (open trangles), 0.6 mg nisin (open squares), and PBS (open circles). Each point represents the mean of data from animals in one dose group. Error bars designate standard errors of the means. Animals were dosed on day 1 and day 2. Statistical analysis confirmed that, between day 2 and day 11, numbers of bifidobacteria in the feces of animals inoculated with either of the L. lactis strains (closed symbols) were higher than in the other three groups (open symbols). (B) Densities of enterococci/streptococci in intestinal samples from rats 25 days after dosage with nisin-producing L. lactis (black), non-nisin-producing L. lactis (gray), 60 mg nisin (white), 0.6 mg nisin (dots), and PBS (stripes). Each point represents the mean of data from animals in one dose group. Error bars designate standard errors of the means. Statistical analysis confirmed that the densities of enterococci/streptococci in all sections of the gut were lower in animals dosed with either of the L. lactis strains (black and gray shaded bars) than in the other three groups.

FIG. 2.

Dendrograms generated by unweighted-pair group method using average linkages cluster analysis of PCR-DGGE profiles of 16S rRNA obtained from fecal samples of HFA rats inoculated as given in Table 1. Samples were taken an hour before first inoculation (A), 1 day after last inoculation (B), and 3 days after last inoculation (C). Numbers 1 to 19 designate the individual animals.