Lactic Acid Bacteria - A Promising Tool for Controlling Chicken Campylobacter Infection

Abstract

Since 2005, campylobacteriosis has been the most common zoonotic disease in Europe. The main reservoir of pathogenic Campylobacter strains is broilers, which makes raw and undercooked poultry meat two major sources of disease. Infection in chicken flocks is most often asymptomatic, despite a high level of colonization reaching 10⁶-10⁹cfu/g in animal ceca. It is widely believed that controlling the level of colonization of the birds' digestive tract by pathogenic strains is a good way to increase food safety. Many treatments have been proposed to combat or at least reduce the level of colonization in animals reservoirs: probiotics, bacteriophages, vaccines, and anti-Campylobacter bacteriocins. This review focuses on the effects of Campylobacter infection on the chicken microbiome and colonization control strategies using probiotics (mostly lactic acid bacteria, LAB), which are live microorganisms included in the diet of animals as feed additives or supplements. Probiotics are not only an alternative to antibiotics, which were used for years as animal growth promoters, but they also constitute an effective protective barrier against excessive colonization of the digestive system by pathogenic bacteria, including Campylobacter. Moreover, one of the many beneficial functions of probiotics is the ability to manipulate the host's microbiota. Recently, there have also been some promising attempts to use lactic acid bacteria as a delivery system of oral vaccine against Campylobacter. Recombinant LAB strains induce primarily a mucosal immune response against foreign antigens, accompanied by at most a low-level immune response against carrier strains. Since the main barrier against the invasion of pathogens in the gastrointestinal tract is the intestinal mucosal membrane, the development of effective oral vaccines to protect animals against enteric infection is very reasonable.

Keywords: Campylobacter; lactic acid bacteria; microbiome; poultry; probiotic.

Figure 1

Age-related changes in the chicken cecal microbiota (from hatch to 42days of age) and potential impact of Campylobacter jejuni colonization that could affect microbiota composition. After hatch, the microbiota is mainly composed of environmental bacteria. Stabilization of the microbial diversity occurs after 10–20days post-hatch. The diagram is based on the information provided by (Oakley et al., 2014a; Thibodeau et al., 2015; Connerton et al., 2018; Richards et al., 2019; Duquenoy et al., 2020). The distribution of the most common and abundant bacterial taxa (phylum, order, and family) in the ceca of the chickens is presented.

Figure 2

Overview of mechanisms of probiotics’ action. Probiotics exert their beneficial effects mainly by ensuring the proper balance of the microbiota colonizing the gut. Probiotic activity depends on stabilization of the epithelial barrier, induction of mucin secretion, and aggregation skills. By adhering to enterocytes, they reduce the opportunity for the colonization of this ecological niche by pathogenic bacteria. They also produce various, not always fully characterized, metabolites that inhibit the growth of pathogens. Additionally, they modulate the host immune system. Probiotics influence the gut through one or a combination of these mechanisms. Dotted arrow underlines the interplay between the host microbiota and probiotic strains and nature of these interactions can be both – positive, negative, depending on the composition of resident gut microbiota and used probiotic. DC, dendritic cells.

Figure 3

Schematic representation of strategies for the cloning of C. jejuni genes for secretory expression in Lactococcus lactis: (A) Campylobacter protein covalently attached to peptidoglycan via the CWA domain from M6 or YndF proteins; (B) Campylobacter protein non-covalently attached to peptidoglycan via LysM domains from AcmA protein; and (C) secreted Campylobacter protein fused to labile enterotoxin subunit B domain. Transcription of the cloned genes is driven by an nisin-inducible P_nisA promoter or strong, constitutive P_usp45 promoter. SP_usp45 – signal peptide of Usp45, the major Sec-dependent protein secreted by L. lactis.