MOLECULAR BIOLOGY AND GENOMICS OF FOODBORNE PATHOGENS
Location: Produce Safety and Microbiology Research
Title: Autoinducer-2 production in Campylobacter jejuni contributes to chicken colonization
Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 6, 2008
Publication Date: January 1, 2009
Citation: Quinones, B., Miller, W.G., Bates, A.H., Mandrell, R.E. 2009. Autoinducer-2 production in Campylobacter jejuni contributes to chicken colonization. Applied and Environmental Microbiology. 75/1:281-285
Infections caused by bacterial foodborne pathogens continue to be a serious health issue and is an area of increasing concern in food safety. A significant contributor to human gastrointestinal infections is the bacterial foodborne pathogen Campylobacter jejuni. A major source of campylobacteriosis is the consumption of undercooked poultry products. C. jejuni colonizes preferentially the avian gastrointestinal tract in a commensal relationship. During the slaughtering process, the gastrointestinal contents can be released and contaminate the chicken meat products. Furthermore, several studies have shown that a large proportion of retail chicken products contain C. jejuni. Thus, a better understanding of processes that contribute to the growth and survival of C. jejuni in chickens could lead to efficient intervention strategies for reducing C. jejuni population sizes in this natural reservoir.
Bacterial populations are capable of coordinating the expression of virulence factors and metabolites that mediate successful colonization of the host by a process known as quorum sensing. In this process, bacteria sense their local population density by detecting the presence of small diffusible signal molecules and responding with changes in gene expression in a cell-density-dependent manner. The signal molecule produced by most pathogenic enteric bacteria is autoinducer 2 (AI-2). AI-2 is a collection of interchangeable molecules derived from a single compound, which is synthesized by a key enzyme known as LuxS. In contrast to other quorum sensing signaling molecules, LuxS functions as an integral component of the activated methyl cycle; therefore, AI-2 synthesis is connected to cellular metabolism and may provide information about the fitness of the bacterial population. The fact that both gram-positive and gram-negative bacteria produce AI-2 has lead to the proposal that AI-2 is a universal signal for interspecies communication. Recent studies that examined AI-2-controlled phenotypes in pathogenic bacteria demonstrated that AI-2 production is implicated in regulating ‘niche-specific’ functions for host colonization and virulence.
Several reports have recently examined the AI-2-dependent signaling in C. jejuni. AI-2 production in C. jejuni was demonstrated to regulate motility and cytolethal distending toxin production. In a recent report, AI-2 production was detected in foods, such as chicken broth and milk, providing the first evidence of this signaling molecule in this environment. To further understand the contribution of AI-2 production in C. jejuni on host colonization and interactions with epithelial cells, the present study characterized a luxS mutation in C. jejuni strain 81-176. We provide evidence that AI-2 production in C. jejuni promotes the colonization and survival in the lower gastrointestinal tract of chickens and the in vitro adherence to chicken hepatocellular cells and differentially regulates the chemotactic behavior toward amino acids and organic acids.
The bacterial foodborne pathogen Campylobacter jejuni is considered to be a significant contributor to human gastrointestinal infections worldwide. C. jejuni are associated prominently with poultry by colonizing preferentially the avian gastrointestinal tract. A major source of C. jejuni infections in humans is thought to be due to the consumption and handling of undercooked poultry products. To further identify mechanisms that may contribute to the colonization of the chicken host, the present study examined autoinducer-2 (AI-2) production in C. jejuni strain 81-176. A mutation in luxS, encoding an AI-2 biosynthesis enzyme, was constructed. Inactivation of luxS in strain 81-176 eliminated extracellular AI-2 production and diminished swarming motility. To examine the role of AI-2 production in chicken colonization, 3-day old chicks were inoculated with either the wild-type or the luxS mutant strain. The results from two independent trials showed that the luxS mutant was impaired in its ability to colonize the lower gastrointestinal tract when compared to the wild type. Significant differences in colonization were observed 7 days after inoculation. Furthermore, analysis of the chemotactic response to amino acids and organic acids demonstrated that the wild type displayed a stronger chemotactic behavior towards organic acids than the luxS mutant. In contrast, the luxS mutant showed significantly greater chemotaxis towards certain amino acids. To examine interactions with host eukaryotic cells, an in vitro adherence assay was performed by using LMH chicken hepatocellular cells. The results demonstrated that the ability of the luxS mutant to adhere to LMH cells was reduced substantially, and adherence was recovered partially by complementation with an intact copy of luxS. Based on these observations, AI-2 production in C. jejuni contributes to the colonization and survival in chickens and regulates traits with an important role in interactions of C. jejuni with host epithelial cells