Lipopolysaccharide O-chain microheterogeneity of Salmonella serotypes enteritidis and typhimurium

Variability in the lipopolysaccharide (LPS) of the two most prevalent Salmo nella serotypes causing foodborne salmonellosis was assessed using gas chro matography analysis of neutral sugars from 43 Salmonella enterica serovar E nteritidis (S. Enteritidis) and 20 Salmonella enterica serovar Typhimurium (S. Typhimurium) isolates. Four substantially different types of O-chain ch emotypes were detected using cluster analysis of sugar compositions; these were low-molecular-mass (LMM) LPS, glucosylated LMM LPS, high-molecular-mas s (HMM) LPS and glucosylated HMM LPS. Nineteen out of 20 S. Typhimurium iso lates yielded glucosylated LMM. In contrast, S. Enteritidis produced a more diverse structure, which varied according to the source and history of the isolate: 45.5% of egg isolates yielded glucosylated HMM LPS; 100% of store d strains lacked glucosylation but retained chain length in some cases; and 83.3% of fresh isolates from the naturally infected house mouse Mus muscul us produced glucosylated LMM LPS. A chain length determinant (wzz) mutant o f S. Enteritidis produced a structure similar to that of S. Typhimurium and was used to define what constituted significant differences in structure u sing cluster analysis. Fine mapping of the S. Enteritidis chromosome by mea ns of a two-restriction enzyme-ribotyping technique suggested that mouse is olates producing glucosylated LMM LPS were closely related to orally invasi ve strains obtained from eggs, and that stored strains were accumulating ge netic changes that correlated with suppression of LPS O-chain glucosylation . These results suggest that the determination of LPS chemotype is a useful tool for epidemiological monitoring of S. Enteritidis, which displays an u nusual degree of diversity in its LPS O-chain.