Bacterial Composition, Genotoxicity, and Cytotoxicity of Fecal Samples from Individuals Consuming Omnivorous or Vegetarian Diets

Abstract

This study analyzes the composition of viable fecal bacteria and gut toxicology biomarkers of 29 healthy volunteers, who followed omnivorous, lacto-ovo-vegetarian, or vegan diets. In particular, the research was focused on the prevalence of some representative viable bacteria from the four dominant phyla (Firmicutes, Bacteroidetes, Proteobacteria, Actinobacteria) commonly present in human feces, in order to evaluate the relationship between microorganisms selected by the habitual dietary patterns and the potential risk due to fecal water (FW) genotoxicity and cytotoxicity, considered as biomarkers for cancer risk and protective food activity. The relative differences of viable bacteria among dietary groups were generally not statistically significant. However, compared to omnivores, lacto-ovo-vegetarians showed low levels of total anaerobes. Otherwise, vegans showed total anaerobes counts similar to those of omnivores, but with lower number of bifidobacteria and the highest levels of bacteria from the Bacteroides-Prevotella genera. FW genotoxicity of lacto-ovo-vegetarians resulted significantly lower either in relation to that of omnivores and vegans. Lacto-ovo-vegetarians also showed the lowest levels of cytotoxicity, while the highest were found for vegans. These results highlighted that lacto-ovo-vegetarian diet was particularly effective in a favorable modulation of microbial activity, thus contributing to a significant reduction of the genotoxic and cytotoxic risk in the gut.

Keywords: cytotoxicity; fecal water; genotoxicity; omnivores; vegetarian diet; viable fecal bacteria.

FIGURE 1

Frequency distribution of genotoxicity (A) and cytotoxicity (B) levels observed for fecal water samples from omnivores, lacto-ovo-vegetarians, and vegans. Only data relative to subjects showing no significant change in the samples of the 2 weeks are included. For each box the arrow indicates an approximation to normality in the first part of the figure.

FIGURE 2

Relative quantification of genotoxic effect in fecal waters samples of omnivores (O), lacto-ovo-vegetarians (L), vegans (V), and negative controls (C-). Box and Whisker plots with median, 25–75th percentiles, range and mean as “+”. DNA tail intensity of positive controls (0.75 μM 4-NQO instead of FW) was 10.34 ± 2.36. The p-values were obtained by unpaired t-test.

FIGURE 3

Relative quantification of cytotoxic effect in fecal waters samples of omnivores (O), lacto-ovo-vegetarians (L), and vegans (V). Box and Whisker plots with median, 25-75th percentiles, range and mean as “+”. The p-values were obtained by unpaired t-test.

FIGURE 4

Relation between fecal water cytotoxicity and genotoxicity. The overall analysis of 52 samples from omnivores (), lacto-ovo-vegetarians (), and vegans () showed no significant regression (y = 1.34 + 0.003x) and correlation (r = 0.049). The dashed lines delimit the reference levels for the normality approximation (see Figure 1). (A) low cytotoxicity, high genotoxicity; (B) high cytotoxicity and genotoxicity; (C) low cytotoxicity and genotoxicity; (D) high cytotoxicity, low genotoxicity.