Elsevier

Vaccine

Volume 35, Issue 24, 31 May 2017, Pages 3204-3208
Vaccine

Microbial compositional changes in broiler chicken cecal contents from birds challenged with different Salmonella vaccine candidate strains

https://doi.org/10.1016/j.vaccine.2017.04.073Get rights and content

Abstract

Previously, we constructed and characterized the vaccine efficacy of Salmonella Typhimurium mutant strains in poultry with either inducible mviN expression (PBAD-mviN) or methionine auxotrophy (ΔΔmetRmetD). The aim of the present study was to assess potential impact of these Salmonella vaccine strains on the cecal microbiota using a next generation sequencing (NGS). The cecal microbial community obtained from unvaccinated (group 1) and vaccinated chickens (group 2, vaccinated with PBAD-mviN; group 3, vaccinated with wild type; group 4, vaccinated with ΔΔmetRmetD) were subjected to microbiome sequencing analysis with an Illumina MiSeq platform. The NGS microbiome analysis of chicken ceca revealed considerable changes in microbial composition in the presence of the different vaccine strains and exhibited detectable patterns of distinctive clustering among the respective groups (the R value of unweighted PCoA plot was 0.68). The present study indicates that different S. Typhimurium vaccine strains can differentially influence the microbiota of the ceca in terms of presence but not in the relative abundance of microbiota.

Introduction

Microbiological safety of food has become a global public health issue to both the consumers and the food industry. Salmonella is one of the more prominent foodborne pathogens and a major cause of foodborne illness. Approximately 56,000 hospitalizations occur with non-typhoidal Salmonella being the leading cause of these hospitalizations, and of deaths, due to foodborne illness [1]. Globally, the number of non-typhoidal Salmonella foodborne illnesses is estimated to be 80.3 million per year, with 155,000 deaths per year [2]. Chicken meat and eggs have been reported as a major source of Salmonella contamination, thus it is important to control Salmonella in those products [3], [4].

Vaccination is one of the most effective methods to control Salmonella and two types of vaccine including live attenuated and killed bacterin are now commercially available [5], [6]. Live attenuated strains have been more effective than killed bacterin, especially those harboring defined deletions in genes that limit the ability to survive intracellularly [6], [7]. For example, deletions in genes involved in carbohydrate metabolism or various forms of auxotrophy have been developed. These mutations attenuate the pathogenicity while allowing adhesion, colonization, and invasion of host tissues to stimulate cell-mediated immunity [7]. In our previous study, we developed a programmed lysis system in Salmonella Typhimurium targeting a different gene of peptidoglycan biosynthesis, mviN and this live attenuated vaccine strain was effective in controlling Salmonella in challenged birds [6]. Our laboratory also constructed a vaccine strain S. Typhimurium with methionine auxotrophy (ΔΔmetRmetD) expecting that the metR and metD deletion could also reduce the ability of a Salmonella to survive in the host by limiting the ability to take in methionine via the remaining methionine transporters.

Another aspect of Salmonella control is the impact on gut microbial diversity. The chicken ceca are not only a primary colonization site for Salmonella but serve as fermentation chambers for polysaccharide digestion, water adsorption and urea recycling [8], [9] as well as harboring as many as 700 distinguishable bacterial species as evidenced by 16S rRNA amplicon pyrosequencing [10]. Several studies have indicated that Salmonella colonization in the host can also directly alter the gut microbiome [11], [12], [13], [14]. This is important since microbiota in the gut may play an important role in host health. Therefore, the next logical step of developing vaccine strains is to examine their various effects on the host cecal microbiome. A significant lack of knowledge exists regarding the impact of vaccine strains such as these on the normal microbiota in chicken ceca. This potential interaction may be important since live attenuated Salmonella vaccines inhabit the ceca and persist in the environment.

In the present study, we compared bacterial compositional changes in ceca of unvaccinated and vaccinated chickens with a wild type Salmonella UK-1 (positive control) and two mechanistically distinct vaccine strains namely, a methionine auxotrophic mutant (ΔΔmetRmetD recently constructed in our laboratory) and a mutant strain PBAD-mviN (vaccine strain which was initially introduced in our previous research [6]) using a next generation sequencing (NGS) to assess potential impact of the Salmonella vaccine strains on the cecal microbiota.

Section snippets

Bacterial strains

A wild type S. Typhimurium UK-1 strain had previously been utilized to construct potential vaccine strains and a nalidixic acid (NA) resistant S. Typhimurium UK-1 derived from the wild type was used as the challenge strain. The PBAD-mviN vaccine strain generated from UK-1 as described in our previous report was used in our previous challenge study [6]. A double deletion mutant affecting methionine metabolism was also recently constructed from S. Typhimurium strain UK-1 (data not shown) using

Results and discussion

Recently, a novel vaccine strain with arabinose-inducible expression of mviN was constructed for the first time and we reported effective vaccine capacity in immunogenicity and colonization control in broiler chickens [6]. A Salmonella oral challenge strain in the ceca from vaccinated chicken with PBAD-mviN was reported to be significantly lower than that from unvaccinated chicken or vaccinated with wild type [6]. The double mutant strain (ΔΔmetRmetD) initially introduced in this study appeared

Acknowledgments

This work was funded by USDA-SBIR grant award 2012-33610-19529.

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    Co-first author, these authors contributed equally to this work.

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