Cattle intestinal microbiota shifts following Escherichia coli O157:H7 vaccination and colonization

Authors: MIR, RAIES - Orise Fellow; SCHAUT, ROBERT - Orise Fellow; Allen, Heather; Looft, Torey; Loving, Crystal; Kudva, Indira; Sharma, Vijay

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/18/2019
Publication Date: 12/5/2019
Citation: Mir, R.A., Schaut, R.A., Allen, H.K., Looft, T.P., Loving, C.L., Kudva, I.T., Sharma, V.K. 2019. Cattle intestinal microbiota shifts following Escherichia coli O157:H7 vaccination and colonization. PLoS One. 14(12):e0226099. https://doi.org/10.1371/journal.pone.0226099.
DOI: https://doi.org/10.1371/journal.pone.0226099

Interpretive Summary: Cattle carry the foodborne, human disease-causing bacteria Escherichia coli O157:H7 (O157) in their intestines and shed these bacteria in their feces. Foods contaminated with O157-containing cattle feces are the main sources of human infections. Cattle vaccines targeting O157 have potential to reduce O157 shedding in feces by colonized animals. However, both vaccination and colonization with O157 can impact numbers and kinds of bacterial populations (microbiota) that are normally found in cattle intestines. These changes in the intestinal microbiota could affect immune responses and health of cattle. In this study, we evaluated the impact of vaccination and O157 colonization on the diversity of intestinal microbiota and immune responses of cattle. Microbiota analysis of fecal samples (which contains intestinal bacteria) collected from these animals over a 30-day period indicated a significant correlation between vaccination and changes in the intestinal bacterial populations. Vaccinated cattle had higher representation of certain populations (families) of bacteria and higher O157-specific cellular immune responses compared to non-vaccinated, non-O157 colonized cattle. Further investigation of these changes in microbiota and immune responses due to vaccination may assist in the development of optimal vaccine strategies for reducing O157 colonization in cattle.

Technical Abstract: Vaccination-induced O157-specific immune responses have been shown to reduce O157 shedding in cattle. Although O157 colonization is correlated with perturbations in intestinal microbial diversity, it is not yet known whether vaccination against O157 could cause shifts in bovine intestinal microbiota. To understand the impact of O157 vaccination and colonization on intestinal microbial diversity, cattle were vaccinated with two doses of different O157 vaccine formulations. Six weeks post-vaccination, the two vaccinated groups (Vx-Ch) and one non-vaccinated group (NonVx-Ch) were orally challenged with O157. Another group was neither vaccinated nor challenged (NonVx-NonCh). Fecal microbiota analysis over a 30-day period indicated a significant (FDR corrected, p less than 0.05) association of bacterial community structure with vaccination until O157 challenge. Shannon diversity index and species richness were significantly lower in vaccinated compared to non-vaccinated groups after O157 challenge (p less than 0.05). The Firmicutes:Bacteroidetes ratio (p greater than 0.05) was not associated with vaccination but the relative abundance of Proteobacteria was significantly lower (p less than 0.05) in vaccinated calves after O157 challenge. Similarly, Vx-Ch calves had higher relative abundance of Paeniclostridium spp. and Christenellaceae R7 group while Campylobacter spp., and Sutterella spp. were more abundant in NonVx-Ch group post-O157 challenge. Only Vx-Ch calves had significantly higher (p less than 0.001) O157-specific serum IgG but no detectable O157-specific IgA. However, O157-specific IL-10-producing T cells were detected in vaccinated animals prior to challenge, but IFN-gamma-producing T cells were not detected. Neither O157-specific IgG nor IgA were detected in blood or feces, respectively, of NonVx-Ch and NonVx-NonCh groups prior to or post vaccinations. Both Vx-Ch and NonVx-Ch animals shed detectable levels of challenge strain during the course of the study. Despite the lack of protection with the vaccine formulations there were detectable shifts in the microbiota of vaccinated animals before and after challenge with O157.