ARS | Publication request: A VIRULENT ISOLATE OF SALMONELLA ENTERITIDIS PRODUCES A SALMONELLA TYPHI-LIKE LIPOPOLYSACCHARIDE

Submitted to: Journal of Bacteriology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 23, 1997
Publication Date: N/A

Interpretive Summary: The incidence of gastrointestinal disease in people who consumed eggs contaminated with Salmonella enteritidis has risen significantly, and there is a clear need to understand how S. enteritidis has changed. Previous work on the molecular characteristics of the outer membrane of avirulent versus virulent S. enteritidis had indicated that the structure of lipopolysaccharide (LPS) was different between the two variants, and that virulent S. enteritidis produced much more high-molecular-weight O- antigen than did avirulent strains. To prove that there were clear differences in LPS produced by different pathotypes of S. enteritidis, chemical and physical analyses of highly purified LPSs obtained from well- characterized avirulent or virulent variants were performed. Results prove that 1) virulent S. enteritidis which is enhanced in its ability to contaminate eggs produces more smooth LPS than does an isogenic avirulent variant, and that 2) the LPS of virulent S. enteritidis has a structure that is similar in detail to that produced by S. typhi. The body of work that is supported by the results presented here indicate that it is possible to screen for egg-contaminating S. enteritidis that closely resembles S. typhi. This work should impact government agencies that oversee public health (CDC, FDA, FSIS, APHIS, state public health departments) and industries that produce diagnostic reagents and vaccines.

Technical Abstract: The lipopolysaccharide (LPS) of Salmonella enteritidis has been implicated as a virulence factor of this organism (J.G. Petter 1993. Appl. Environ. Microbiol. 59:2884-2890, J. Guard-Petter, et al. 1995. Appl. Environ. Microbiol. 61:2845-2851, J. Guard-Petter, et al. 1996. Epidemiol. Infect. In press.). Therefore, the LPS from a stable virulent isolate, SE6-E21, was compared with that from an avirulent isolate, SE6-E5. The LPSs were extracted and the high molecular weight (HMW) LPS was separated from the low molecular weight (LMW) LPS from both isolates. Both the HMW- and LMW- LPSs were characterized by glycosyl composition and linkage analyses. Immunochemical characterization was performed by western blots using factor 9 antiserum, and with S. typhimurium antiserum which contains factors 1,4,5, and 12-2. In addition, the polysaccharides released by mild acid hydrolysis were isolated and subjected to hydrolysis by bacteriophage P22 which contains endorhamnosidase activity. The resultin oligosaccharides were purified using Bio-Gel P4 gel permeation chromatography and characterized by NMR, fast atom bombardment mass spectrometry (FAB-MS), tandem MS-MS, and matrix assisted laser desorption time of flight (MALDI-TOF) MS. The results show that the HMW-LPS O- antigen polysaccharides from both isolates are comprised of two different repeating units.