The Salmonella Enteritidis TolC outer membrane channel is essential for egg white survival.

Salmonella Enteritidis has developed the potential to contaminate eggs by surviving in the antimicrobial environment of the hen's egg white. This has led to a worldwide pandemic of foodborne salmonellosis infections in humans due to the consumption of contaminated eggs and egg-derived products. The molecular mechanisms of Salmonella Enteritidis egg white survival are not fully clear. Using in vivo expression technology and promoter-reporter fusions we showed that the promoter of the tolC gene, encoding the TolC outer membrane channel that is used by multidrug efflux pumps to export harmful molecules and to secrete bacterial products, is activated by egg white at the chicken body temperature. Using a Salmonella Enteritidis tolC deletion mutant we showed that TolC has an important role in egg white survival. Chromatographic separation techniques and subsequent testing of antimicrobial activities of separated egg white fractions led to the identification of ovotransferrin as the egg white antimicrobial factor which is capable of inhibiting growth of a tolC deletion strain but not the wild type strain. We provide evidence that TolC protects Salmonella Enteritidis against ovotransferrin-mediated growth inhibition in egg white.

Microarray-based detection of Salmonella enterica serovar Enteritidis genes involved in chicken reproductive tract colonization.

Salmonella enterica serovar Enteritidis has developed the potential to contaminate table eggs internally, by colonization of the chicken reproductive tract and internalization in the forming egg. The serotype Enteritidis has developed mechanisms to colonize the chicken oviduct more successfully than other serotypes. Until now, the strategies exploited by Salmonella Enteritidis to do so have remained largely unknown. For that reason, a microarray-based transposon library screen was used to identify genes that are essential for the persistence of Salmonella Enteritidis inside primary chicken oviduct gland cells in vitro and inside the reproductive tract in vivo. A total of 81 genes with a potential role in persistence in both the oviduct cells and the oviduct tissue were identified. Major groups of importance include the Salmonella pathogenicity islands 1 and 2, genes involved in stress responses, cell wall, and lipopolysaccharide structure, and the region-of-difference genomic islands 9, 21, and 40.

A genome-wide screen identifies Salmonella Enteritidis lipopolysaccharide biosynthesis and the HtrA heat shock protein as crucial factors involved in egg white persistence at chicken body temperature.

Eggs contaminated with Salmonella Enteritidis are an important source of human foodborne Salmonella infections. Salmonella Enteritidis is able to contaminate egg white during formation of the egg within the chicken oviduct, and it has developed strategies to withstand the antimicrobial properties of egg white to survive in this hostile environment. The mechanisms involved in the persistence of Salmonella Enteritidis in egg white are likely to be complex. To address this issue, a microarray-based transposon library screen was performed to identify genes necessary for survival of Salmonella Enteritidis in egg white at chicken body temperature. The majority of identified genes belonged to the lipopolysaccharide biosynthesis pathway. Additionally, we provide evidence that the serine protease/heat shock protein (HtrA) appears essential for the survival of Salmonella Enteritidis in egg white at chicken body temperature.

Salmonella Enteritidis is superior in egg white survival compared with other Salmonella serotypes.

Salmonella enterica subspecies enterica serotype Enteritidis is a major cause of egg-borne human salmonellosis. The ability to survive in egg albumen at chicken body temperature was hypothesized to be an important factor involved in the predominant contamination of eggs by this specific serotype. Eighty-nine Salmonella strains from different serotypes, belonging to 5 serogroups, were incubated for 24 h in egg white at 42°C. The number of Salmonella Enteritidis strains that were able to survive in egg white was significantly higher compared with strains belonging to other serotypes and serogroups that were tested in this study. These data add evidence to the hypothesis that egg white survival is one of the reasons why Salmonella Enteritidis is more predominantly isolated from contaminated eggs, and helps explaining why most reported egg-borne Salmonella outbreaks in humans are caused by Salmonella Enteritidis.

Salmonella Enteritidis universal stress protein (usp) gene expression is stimulated by egg white and supports oviduct colonization and egg contamination in laying hens.

Salmonella enterica subspecies enterica serovar Enteritidis has caused a worldwide egg-associated pandemic since the mid 1980s. The exact mechanisms causing this egg tropism are still largely unknown, and only a few Salmonella genes have been implicated in the interaction with the oviduct or eggs. A in vivo expression technology screening performed previously, identified the uspA and uspB genes as being highly expressed in the chicken oviduct and in eggs. Here, we demonstrate that uspA and uspB gene expression is indeed induced after contact with egg white. Intra-oviduct inoculation of Salmonella Enteritidis uspB and uspBA mutant strains showed that the mutants had a decreased ability to colonize the magnum and isthmus of the oviduct, the organs that produce the egg white and eggshell membranes, respectively, at 7 days post-inoculation. Intravenous challenge showed that a Salmonella Enteritidis uspBA mutant strain had a decreased ability to contaminate eggs. Analogous to the function of universal stress proteins A and B in other bacterial species, we hypothesize that the Salmonella uspA and uspB genes are involved in long term persistence of Salmonella Enteritidis in harmful environments, such as in the oviduct and eggs, by conferring resistance against compounds that damage the bacterial cell membrane and DNA.