Stress-induced survival strategies enable Salmonella Enteritidis to persistently colonize the chicken oviduct tissue and cope with antimicrobial factors in egg white: a hypothesis to explain a pandemic

Background: Egg-associated transmission to humans seems to be characteristic of the Salmonella serotype Enteritidis, explaining why this particular serotype has caused a worldwide pandemic since the mid '80s. Salmonella Enteritidis is much more capable to persistently colonize the laying hen reproductive tract and to survive in the hostile egg white, as compared to other serotypes. Presentation of the hypothesis: It is hypothesized that stress-induced survival mechanisms enable the serotype Enteritidis to persistently colonize the oviduct without causing damage and excessive inflammation, and to cope with the antimicrobial compounds present in egg white. Testing the hypothesis: To test the hypothesis first of all Salmonella Enteritidis genes that are essential for colonization of the oviduct and survival in eggs need to be identified. Comparative genomics tools should be used to identify genes or pathogenicity islands that are present in Salmonella Enteritidis and not in the multiple non egg-contaminating serotypes. High-throughput signature-tagged-mutagenesis approaches, coupled to micro-array detection of the genes that lead to an attenuated phenotype when mutated is proposed as an ideal tool to identify genes involved in oviduct colonization and egg white survival. Identifying the stressors and antibacterial molecules in the oviduct and in the egg white that limit colonization or survival of non-Enteritidis serotypes is a second important objective that can theoretically be achieved using screenings of expressed oviduct cDNA libraries for their antibacterial activity against strains from multiple serotypes. Finally, the effect of contact with these stressors in the oviduct or egg white on Salmonella gene expression will need to be analyzed, in order to clarify whether serotype Enteritidis-specific regulation of certain stress-survival pathways are either or not present. Implications of the hypothesis: Knowledge on the pathogenesis of egg infections would furthermore give insights that might be extrapolated to other biological interactions, in which a highly specialized bacterial pathogen resists the host response in a specific biological niche. In addition, this info can be of value in developing early warning criteria to identify emerging egg-associated Salmonella strains and in developing safe live attenuated vaccine strains

In vitro selective growth-inhibitory effect of 8-hydroxyquinoline on Clostridium perfringens versus Bifidobacteria in a medium containing chicken ileal digesta

Clostridium perfringens-induced necrotic enteritis is generally controlled by antibiotics. However, because of increasing antibiotic resistance, other antibacterial agents are required, preferably ones that do not affect the beneficial intestinal microbiota of the host. This study evaluated the in vitro selective growth-inhibitory effect of 8-hydroxyquinoline (8HQ) on C. perfringens vs. bifidobacteria in a medium containing chicken ileal digesta. Prior to the experiments, the minimum inhibitory concentrations of 8HQ and penicillin G were determined by broth microdilution assay. The minimum inhibitory concentration values of 8HQ for C. perfringens were 16-32 times lower than the values for bifidobacteria. Treatment of autoclaved and non-autoclaved chicken ileal digesta with 8HQ showed a selective anticlostridial effect. After incubation of C. perfringens with autoclaved ileal digesta for 3 h, all 8HQ concentrations tested (32-2048 mu g/mL) significantly reduced C. perfringens bacterial count. In contrast, the same treatment had no or only a slight effect on bifidobacteria counts. Unlike 8HQ, penicillin G did not exhibit any selectivity. Similar results were obtained after incubation for 24 h. In non-autoclaved ileal digesta, all 8HQ concentrations tested significantly reduced C. perfringens bacterial counts after incubation for 30 min and 3 h, while no effect was observed on bifidobacteria. These results suggest that 8HQ may serve as a prospective veterinary compound for use against necrotic enteritis in poultry

Butyrate protects Caco-2 cells from Campylobacter jejuni invasion and translocation

Invasion in and translocation across enterocytes are major events during Campylobacter jejuni-induced enteritis in humans. C. jejuni in vitro infection of cell monolayers typically results in loss of tight junction integrity, which could contribute to translocation. In the present study, we wanted to investigate whether butyrate is able to confer protection to Caco-2 cells against C. jejuni invasion, thus reducing paracellular permeability and limiting C. Jejuni translocation. Protection of Caco-2 cells against C. jejuni invasion was assessed using a gentamicin protection assay. Trans-well systems were used to investigate the impact of butyrate on translocation of C. jejuni across a Caco-2 monolayer and its effect on transepithelial resistance during infection. Butyrate protected Caco-2 cells against C. jejuni invasion in a concentration-dependent manner. Differentiated Caco-2 cells were less Susceptible to C. jejuni invasion than 3-d-old undifferentiated cells and higher concentrations of butyrate and longer incubation times were needed to become refractive for invasion. C. jejuni translocation over Caco-2 monolayers was reduced when monolayers were treated with butyrate and this was accompanied by an enhanced drop in transepithelial resistance. The present study showed that butyrate is able to protect Caco-2 cells front two major Virulence mechanisms of C. jejuni, namely invasion and translocation, but not from a decline in transepithelial resistance

Progress and problems in vaccination against necrotic enteritis in broiler chickens

Necrotic enteritis in broilers is caused by Clostridium perfringens type A strains that produce the NetB toxin. Necrotic enteritis is one of the gastrointestinal diseases in poultry that has gained worldwide importance during the last decade due to efforts to improve broiler performance. Prevention strategies include avoiding predisposing factors, such as coccidiosis, and in-feed supplementation with a variety of feed additives. However, vaccination with modified toxin or other secreted immunogenic proteins seems a logical preventive tool for protection against a toxin-producing bacterium. Formalin-inactivated crude supernatant has been used initially for vaccination. Several studies have been carried out recently to identify the most important immunogenic and protective proteins that can be used for vaccination. These include the NetB toxin, as well as a number of other proteins. There is evidence that immunization with single proteins is not protective against severe challenge and that combinations of different antigens are needed. Most published studies have used multiple dosage vaccination regimens that are not relevant for practical use in the broiler industry. Single vaccination regimens for 1-day-old chicks appear to be non-protective. This review describes the history of vaccination strategies against necrotic enteritis in broilers and gives an update on future vaccination strategies that are applicable in the field. These may include breeder hen vaccination, in ovo vaccination and live attenuated vectors to be used in feed or in drinking water

Rethinking our understanding of the pathogenesis of necrotic enteritis in chickens

For decades, low doses of antibiotics have been used widely in animal production to promote growth. However, there is a trend to reduce this use of antibiotics in feedstuffs, and legislation is now in place in Europe to prohibit their use in this way. As a consequence, economically important diseases, such as necrotic enteritis (NE) of chickens, that are caused by Clostridium perfringens have become more prevalent. Recent research is creating a paradigm shift in our understanding of the pathogenesis of NE and is now providing information that will be necessary to monitor and control the incidence of NE in poultry