Location: Produce Safety and Microbiology Research
Title: AI-2 signaling in Campylobacter jejuni and its contribution to chicken colonization Authors
Submitted to: UJNR Food & Agricultural Panel Proceedings
Publication Type: Proceedings
Publication Acceptance Date: August 15, 2007
Publication Date: N/A
Interpretive Summary: Infections caused by bacterial foodborne pathogens continue to be a serious health issue and an area of increasing concern in food safety. A significant contributor to human gastrointestinal infections is the bacterial foodborne pathogen Campylobacter jejuni (1). 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 are exposed and contaminate the chicken meat products. 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 (2). In this process, bacteria sense their local population density, by detecting the presence of small diffusible signal molecules, and respond 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 may be 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 (2). Several reports have examined recently the AI-2-dependent signaling in C. jejuni (2). AI-2 production was demonstrated to regulate motility on semi-solid agar and autoagglutination, a phenomenon shown to be associated with flagella and cell surface hydrophobicity. AI-2 signaling appears to regulate toxin production in C. jejuni since the transcription of genes, encoding the three subunits of cytolethal distending toxin, was reduced in a luxS- mutant (3). In a recent report, AI-2 was detected in foods, such as chicken broth and milk, demonstrating the production of this signaling molecule in the food environment (4). The present study characterized AI-2 production in C. jejuni strain 81-176 and examined the role that this signaling system may have on colonization of a host.
Technical Abstract: To investigate the role of AI-2-mediated signaling in Campylobacter jejuni, a mutation in luxS, encoding an AI-2 biosynthesis enzyme, was constructed. Inactivation of luxS in C. jejuni strain 81-176 eliminated extracellular AI-2 production and diminished swarming motility and autoagglutination. Furthermore, the ability to colonize 3-day old chicks and to chemotax toward organic acids was impaired in the luxS- mutant when compared to the wild type. Both attachment and invasion of intestinal epithelial INT-407 cells were reduced significantly in the luxS- mutant. These results demonstrate that AI-2 production contributes to the colonization and survival in chickens and also regulates functions with an importance in virulence.