Submitted to: Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/25/2001
Publication Date: 5/16/2001
Interpretive Summary: Salmonella serovar Enteritidis (SE) is the only Salmonella bacterium that routinely causes illness in humans by contaminating the internal contents of Grade A eggs of otherwise healthy chickens. In order to understand the unique biology of SE, we analyzed the chemical composition of a complex sugar, called LPS, from a total of 78 strains of Salmonella. We found that tS. Enteritidis produced a wide variety of LPS structures as compared to those recovered from S. Typhimurium, which routinely causes food-borne illness by carcass contamination, or S. Schwarzengrund, which is a pig-associated Salmonella that rarely causes illness in people. The egg, the spleen of the naturally infected house mouse, and storage of strains were 3 environmental conditions that appeared to alter LPS structure of SE. S. Typhimurium did not undergo the same degree of variation. Thus, results were that egg-contaminating SE, which is the leading cause of human salmonellosis in the world, has a significantly different outer membrane from that of S. Typhimurium, which is the second most common cause of human salmonellosis. Generation of changes in the LPS molecule could be a factor that is important for this organism to contaminate eggs. This information can be used to improve epidemiological monitoring of S. Enteritidis in disease outbreaks, to improve vaccines, and to follow adaptation of bacteria to different environmental conditions.
Technical Abstract: Variability in the lipopolysaccharide (LPS) of Salmonella (S.) serotypes causing food-borne salmonellosis was assessed by chemical methods and cluster analysis of 43 S. Enteritidis and 20 S. Typhimurium isolates. 15 isolates of low prevalence S. Schwarzengrund were also analysed. Four substantially different types of LPS O-antigen chemotypes were detected, which were LMW LPS, glucosylated LMW LPS, HMW LPS, and glucosylated HMW LPS. S. Typhimurium and S. Schwarzengrund both produced glucosylated LMW LPS. S. Enteritidis produced a more diverse structure that varied according to source of isolation: 45.5% of egg isolates yielded glucosylated HMW LPS, stored strains lacked glucosylation but retained chain length, and fresh isolates from the naturally infected house mouse produced glucosylated LMW LPS. Mapping of the S. Enteritidis chromosome suggested that mouse isolates could be closely related to orally invasive strains obtained from eggs. These results suggest that determination of LPS chemotype is a useful tool for epidemiological monitoring of S. Enteritidis.