Influence of a nonfavorable environment, egg white, on resistance to heat and disinfectant, adhesion, and virulence of Salmonella enteritidis

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.

Pathogenic potential of Salmonella Typhimurium DT104 following sequential passage through soil, packaged fresh-cut lettuce and a model gastrointestinal tract

From a quantitative microbial risk assessment perspective it is important to know whether certain food environments influence the pathogenic potential of pathogens and to what extent. The purpose of the present study was to examine the pathogenic potential of S. Typhimurium DT104, measured as the capability to survive a simulated gastrointestinal tract system and the capability of adhering to and invading differentiated Caco-2 cells, after sequential incubation (without intermediate culturing) into soil, lettuce and cut lettuce stored under modified atmosphere (MAP) conditions. Two S. Typhimurium DT104 strains were used, one isolated from a pig carcass and one isolated from lettuce. The most important result of the present study is that the sequential incubation of S. Typhimurium in soil and lettuce slightly increased the capability of surviving the simulated gastric fluid, increased the capability to grow in the simulated intestinal fluid but decreased the capability of epithelial attachment and invasion and decreased the overall survival probability of the gastrointestinal tract system. Some variation in responses between the strains was observed, with the lettuce strain maintaining higher epithelial attachment capability and the carcass strains maintaining higher epithelial invasion capability. This study provided quantitative data on the effect of environmental and food matrices on the pathogenic potential of S. Typhimurium DT104 using a realistic system of sequential incubations in environmental and food matrices, followed by simulated gastrointestinal tract passage without intermediate culturing. These results could aid the development of more realistic quantitative microbial risk assessments.

Survival and growth of Salmonella Enteritidis in liquid egg products varying by temperature, product composition, and carbon dioxide concentration

Cryogenic cooling of shell eggs with carbon dioxide (CO(2)) is known to improve egg content quality through rapid cooling as well as by increasing internal CO(2) levels. A study was undertaken to determine the effects of variations in atmospheric CO(2) concentrations (aerobically stored, flushed with CO(2) and sealed, or bubbled with CO(2)) on the survival and growth of Salmonella Enteritidis in liquid egg products including whole egg, albumen, yolk, and albumen + 1% yolk. Egg products were inoculated with a three-strain composite of Salmonella Enteritidis at ca. 4 log colony-forming units (CFU)/mL and stored at 7 degrees C or 10 degrees C for 8 or 4 days, respectively, or at ca. 2 log CFU/mL and stored at 23 degrees C and 37 degrees C for 48 or 24 hours, respectively. Salmonella populations differed based on variations in liquid egg composition (p < 0.05). Manipulating the atmospheric concentrations of CO(2) in which liquid egg products were stored did not significantly inhibit the growth of Salmonella Enteritidis (p > 0.05) in yolk-containing egg products or affect the inhibitory activity of albumen-containing products. Populations of Salmonella were static at 7 degrees C over the entire storage period and significant growth occurred in whole egg and yolk stored at 10 degrees C. Populations in egg stored at 23 degrees C and 37 degrees C were greater in yolk than in whole egg, although whole egg had populations greater than in albumen or albumen +1% yolk (p < 0.05). Results of this investigation suggest that increasing atmospheric CO(2) to enhance egg quality should not promote the growth of Salmonella Enteritidis in eggs.

Isolated or associated experimental contamination of albumen and egg yolk for Salmonella Enteritidis and Escherichia coli: influence of temperature and storage time

The behavior of Salmonella enteritidis (SE) and Escherichia coli in albumen and yolk of chicken eggs submitted to two different temperatures, 8ºC and 30ºC, when separately inoculated or in the form of mixed cultures was studied. There was no difference in the behaviour of the tested agents even when inoculated together. Even under high temperature, E. coli did not multiply in the albumen, demonstrating the inhibition power for that microorganism, while SE increased its population up to three logarithmic cycles. In egg yolk, SE demonstrated psychrotrophic characteristics.