Campylobacter contaminated broiler chicken meat is an important source of foodborne gastroenteritis and poses a serious health burden in industrialized countries. Broiler chickens are commonly regarded as a natural host for this zoonotic pathogen and infected birds carry a very high C. jejuni load in their gastrointestinal tract, especially the ceca. This eventually results in contaminated carcasses during processing. Current intervention methods fail to reduce the colonization of broiler chicks by C. jejuni due to an incomplete understanding on the interaction between C. jejuni and its avian host. Clearly, C. jejuni developed several survival and colonization mechanisms which are responsible for its highly adapted nature to the chicken host. But how these mechanisms interact with one another, leading to persistent, high-level cecal colonization remains largely obscure. A plethora of mutagenesis studies in the past few years resulted in the identification of several of the genes and proteins of C. jejuni involved in different aspects of the cellular response of this bacterium in the chicken gut. In this review, a thorough, up-to-date overview will be given of the survival mechanisms and colonization factors of C. jejuni identified to date. These factors may contribute to our understanding on how C. jejuni survival and colonization in chicks is mediated, as well as provide potential targets for effective subunit vaccine development.

Campylobacteriosis is the most reported foodborne gastroenteritic disease and poses a serious health burden in industrialized countries. Disease in humans is mainly caused by the zoonotic pathogen Campylobacter jejuni. Due to its wide-spread occurrence in the environment, the epidemiology of Campylobacter remains poorly understood. It is generally accepted, however, that chickens are a natural host for Campylobacter jejuni, and for Campylobacter spp. in general, and that colonized broiler chicks are the primary vector for transmitting this pathogen to humans. Several potential sources and vectors for transmitting C. jejuni to broiler flocks have been identified. Initially, one or a few broilers can become colonized at an age of > 2 weeks until the end of rearing, after which the infection will rapidly spread throughout the entire flock. Such a flock is generally colonized until slaughter and infected birds carry a very high C. jejuni load in their gastrointestinal tract, especially the ceca. This eventually results in contaminated carcasses during processing, which can transmit this pathogen to humans. Recent genetic typing studies showed that chicken isolates can frequently be linked to human clinical cases of Campylobacter enteritis. However, despite the increasing evidence that the chicken reservoir is the number one risk factor for disease in humans, no effective strategy exists to reduce Campylobachter prevalence in poultry flocks, which can in part be explained by the incomplete understanding of the epidemiology of C. jejuni in broiler flocks. As a result, the number of human campylobacteriosis cases associated with the chicken vector remains strikingly high.

Campylobacter strains pathogenic to human (Friis et al., 2010) and broiler chicken meat 5 contaminated with this pathogen is believed to be responsible for up to 40% of human 6 campylobacteriosis cases (EFSA, 2010a). 7Campylobacter is highly prevalent among broiler flocks with on average 60% to 80% of 8 the analyzed flocks being colonized with the bacterium at slaughter age in the EU (Evans and 9 Sayers, 2000; Herman et al., 2003;Rasschaert et al., 2006;Reich et al., 2008; EFSA, 2010c). 10Primary infection of broilers probably occurs through horizontal transmission from the 11 environment (Jacobs-Reitsma et al., 1995). Potential sources and vectors for contamination 12 are infected livestock and free-living animals (van de Giessen et al., 1996; Zweifel et al., 13 2008; Ellis-Iversen et al., 2009), rodents and flies (Hald et al., 2008; Hazeleger et al., 2008), 14 contaminated surface water (Messens et al., 2009) and personnel and farm equipment 15 (Ramabu et al., 2004) at the farm. Also partial thinning of broiler flocks has been implicated 16 as a potential risk factor for Campylobacter colonization of the remainder of the animals, due 17 to difficulties in maintaining biosecurity during thinning (Allen et al., 2008). Most flocks 18 become colonized at an age of two to four weeks only (Jacobs-Reitsma et al., 1995; Evans 19 and Sayers, 2000; Herman et al., 2003; van Gerwe et al., 2009). The majority of the birds in a 20 flock are colonized within only a few days after the first chick is infected (van Gerwe et al., 21 2009). These broiler chickens carry high C. jejuni numbers in their intestinal tract, especially 22 in the ceca (between 10 6 to 10 8 CFU/g or higher), and remain colonized until slaughter (Beery 23 et al., 1988;Jacobs-Reitsma et al., 1995; Evans and Sayers, 2000). 24 4 Intestinal colonization of broiler chickens with Campylobacter during rearing is 1 responsible for the contamination of the carcasses after processing (Herman et al., 2003; 2 Rasschaert et al., 2006; Rosenquist et al., 2006;Reich et al., 2008). Worldwide, an average 3 prevalence of Campylobacter contamination on poultry carcasses is reported to be in the 4 range of 60% to 80% (Suzuki and Yamamoto, 2009; EFSA, 2010c). Carcass contamination 5 occurs during defeathering and evisceration, by contaminated feces leaking from the cloaca 6 and visceral rupture of the ceca carrying a high Campylobacter load (Berrang et al., 2001; 7 Smith et al., 2007; Allen et al., 2008;Boysen and Rosenquist, 2009). In addition, carcasses 8 can become contaminated by cross-contamination of Campylobacter strains between 9 slaughtered flocks (Allen et al., 2008;Normand et al., 2008). 10 11 Campylobacter control in poultry 12 13In the past few years, several quantitative risk assessments for Campylobacter in poultry 14 meat have been developed as a guidance tool to control the presence of this zoonotic pathogen 15 throughout the poultry meat production chain (Nauta et al., 2009). Although there is 16 considerable variation between countrie...

Campylobacter jejuni is the most common cause of bacterial-mediated diarrheal disease worldwide. Because poultry and poultry products are a major source of C. jejuni infections in humans, efforts should be taken to develop strategies to decrease Campylobacter shedding during primary production. For this purpose, the efficacy of medium-chain fatty acids (MCFA) as feed additives to control C. jejuni colonization in broiler chickens was analyzed. First, the antimicrobial activity of the MCFA caproic, caprylic, and capric acid on C. jejuni was evaluated in vitro. Minimal inhibitory concentrations were 0.25 mM for caproic and 0.5 mM for caprylic and capric acids at pH 6.0 and 4 mM for all 3 compounds at pH 7.5. Time-kill curves revealed strong bactericidal properties of the tested compounds toward C. jejuni at pH 6.0. Concentrations as low as 4 mM caprylic and capric acids and 16 mM caproic acid killed all bacteria within 24 h. Capric acid had the highest activity, with concentrations of 4 mM killing all bacteria within the hour. Together these data show a profound bactericidal, dose-dependent activity of the tested MCFA toward C. jejuni in vitro. For this reason, the effect of these 3 MCFA on C. jejuni was evaluated in vivo. The addition of any of the acids to the feed, from 3 d before euthanization, was not capable of reducing cecal Campylobacter colonization in 27-d-old broilers experimentally infected with C. jejuni at 15 d of age. Using a cecal loop model, sodium caprate was not able to reduce cecal Campylobacter counts. When time-kill curves were conducted in the presence of chick intestinal mucus, capric acid was less active against C. jejuni. At 4 mM, all bacteria were killed only after 24 h. Thus, despite the marked bactericidal effect of MCFA in vitro, supplementing these acids to the feed does not reduce cecal Campylobacter colonization in broiler chickens under the applied test conditions, probably due to the protective effect of the mucus layer.

Campylobacter jejuni is the most common cause of bacterium-mediated diarrheal disease in humans worldwide. Poultry products are considered the most important source of C. jejuni infections in humans but to date no effective strategy exists to eradicate this zoonotic pathogen from poultry production. Here, the potential use of passive immunization to reduce Campylobacter colonization in broiler chicks was examined. For this purpose, laying hens were immunized with either a whole-cell lysate or the hydrophobic protein fraction of C. jejuni and their eggs were collected. In vitro tests validated the induction of specific ImmunoglobulinY (IgY) against C. jejuni in the immunized hens’ egg yolks, in particular. In seeder experiments, preventive administration of hyperimmune egg yolk significantly (P < 0.01) reduced bacterial counts of seeder animals three days after oral inoculation with approximately 104 cfu C. jejuni, compared with control birds. Moreover, transmission to non-seeder birds was dramatically reduced (hydrophobic protein fraction) or even completely prevented (whole-cell lysate). Purified IgY promoted bacterial binding to chicken intestinal mucus, suggesting enhanced mucosal clearance in vivo. Western blot analysis in combination with mass spectrometry after two-dimensional gel-electrophoresis revealed immunodominant antigens of C. jejuni that are involved in a variety of cell functions, including chemotaxis and adhesion. Some of these (AtpA, EF-Tu, GroEL and CtpA) are highly conserved proteins and could be promising targets for the development of subunit vaccines.