Oxygen restriction increases the infective potential of Listeria monocytogenes in vitro in Caco-2 cells and in vivo in guinea pigs

<p>Abstract</p> <p>Background</p> <p>Listeria monocytogenes has been implicated in several food borne outbreaks as well as sporadic cases of disease. Increased understanding of the biology of this organism is important in the prevention of food borne listeriosis.</p> <p>The infectivity of <it>Listeria monocytogenes </it>ScottA, cultivated with and without oxygen restriction, was compared in <it>vitro </it>and <it>in vivo</it>. Fluorescent protein labels were applied to allow certain identification of <it>Listeria </it>cells from untagged bacteria in <it>in vivo </it>samples, and to distinguish between cells grown under different conditions in mixed infection experiments.</p> <p>Results</p> <p>Infection of Caco-2 cells revealed that <it>Listeria </it>cultivated under oxygen-restricted conditions were approximately 100 fold more invasive than similar cultures grown without oxygen restriction. This was observed for exponentially growing bacteria, as well as for stationary-phase cultures.</p> <p>Oral dosage of guinea pigs with <it>Listeria </it>resulted in a significantly higher prevalence (p < 0.05) of these bacteria in jejunum, liver and spleen four and seven days after challenge, when the bacterial cultures had been grown under oxygen-restricted conditions prior to dosage. Additionally, a 10–100 fold higher concentration of <it>Listeria </it>in fecal samples was observed after dosage with oxygen-restricted bacteria. These differences were seen after challenge with single <it>Listeria </it>cultures, as well as with a mixture of two cultures grown with and without oxygen restriction.</p> <p>Conclusion</p> <p>Our results show for the first time that the environmental conditions to which <it>L. monocytogenes </it>is exposed prior to ingestion are decisive for its <it>in vivo </it>infective potential in the gastrointestinal tract after passage of the gastric barrier. This is highly relevant for safety assessment of this organism in food.</p

Characterization of Campylobacter phages including analysis of host range by selected Campylobacter Penner serotypes

Background: The predominant food borne pathogen in the western world today is Campylobacter. Campylobacter specific bacteriophages (phages) have been proposed as an alternative agent for reducing the burden of Campylobacter in broilers. One concern in relation to phage biocontrol is the narrow host range often displayed by phages. To identify the potential of phages as a Campylobacter reducing agent we needed to determine their infectivity on a panel of isolates representing the Campylobacter strains found in broilers as well as humans. Results: In this study, Campylobacter phages were isolated from the intestines of broilers and ducks and from abattoir sewage. Twelve phages were investigated to determine their ability to infect the Campylobacter Penner serotypes commonly present in Danish poultry and patients with campylobacteriosis. A total of 89% of the Campylobacter jejuni strains and 14% of the Campylobacter coli strains could be infected by at least one of the bacteriophages. The majority of the phages infected the most common serotypes in Danish broilers (O:1,44; O:2; O:4-complex), but showed limited ability to infect 21 of the less frequent Campylobacter serotypes. Pulse field gel electrophoresis (PFGE) and restriction endonuclease analysis (REA) were used to characterize the phage genomes. Three categories of bacteriophages were observed. I: a genome size of similar to 194 kb and refractory to digestion with HhaI; II: a genome size of similar to 140 kb and digestible by HhaI; and III: a genome size undeterminable in PFGE. The categorization of the phages correlated with the host range patterns displayed by the phages. Six phages were subjected to transmission electron microscopy (TEM). They all belonged to the family of Myoviridae. Conclusion: We have characterized and identified the host range of 12 Danish Campylobacter phages. Due to their ability to infect the majority of the common serotypes in Denmark we suggest the phages can become an effective agent in the effort to reduce the incidence of campylobacteriosis in Denmark. This study provides the basis for future experiments in Campylobacter phages and knowledge for the selection of Campylobacter phages for biocontrol in broilers

Quantifying the effect of natural microflora on growth of salmonellae in fresh pork

This study was undertaken to provide predictive models to help prevent health problems in relation to salmonellae in fresh pork. The models consider different time and temperature of storage as well as microbial interaction with the natural microflora in the meat. At six temperatures between 4 and 20°C, duplicate growth curves of Salmonella Typhimurium DT104 and Salmonella Derby were established in both sterile (irradiated) minced pork as well as in minced pork with a natural microflora

Phase variable expression of capsular polysaccharide modifications allows <em>Campylobacter jejuni</em> to avoid bacteriophage infection in chickens

Bacteriophages are estimated to be the most abundant entities on earth and can be found in every niche where their bacterial hosts reside. The initial interaction between phages and Campylobacter jejuni, a common colonizer of poultry intestines and a major source of foodborne bacterial gastroenteritis in humans, is not well understood. Recently, we isolated and characterized a phage F336 resistant variant of C. jejuni NCTC11168 called 11168R. Comparisons of 11168R with the wildtype lead to the identification of a novel phage receptor, the phase variable O-methyl phosphoramidate (MeOPN) moiety of the C. jejuni capsular polysaccharide (CPS). In this study we demonstrate that the 11168R strain has gained cross-resistance to four other phages in our collection (F198, F287, F303, and F326). The reduced plaquing efficiencies suggested that MeOPN is recognized as a receptor by several phages infecting C. jejuni. To further explore the role of CPS modifications in C. jejuni phage recognition and infectivity, we tested the ability of F198, F287, F303, F326, and F336 to infect different CPS variants of NCTC11168, including defined CPS mutants. These strains were characterized by high-resolution magic angle spinning NMR spectroscopy. We found that in addition to MeOPN, the phase variable 3-O-Me and 6-O-Me groups of the NCTC11168 CPS structure may influence the plaquing efficiencies of the phages. Furthermore, co-infection of chickens with both C. jejuni NCTC11168 and phage F336 resulted in selection of resistant C. jejuni bacteria, which either lack MeOPN or gain 6-O-Me groups on their surface, demonstrating that resistance can be acquired in vivo. In summary, we have shown that phase variable CPS structures modulate phage infectivity in C. jejuni and suggest that the constant phage predation in the avian gut selects for changes in these structures leading to a continuing phage–host co-evolution