A VIRULENT ISOLATE OF SALMONELLA-ENTERITIDIS PRODUCES A SALMONELLA TYPHI-LIKE LIPOPOLYSACCHARIDE

The lipopolysaccharide (LPS) of Salmonella enteritidis has been implic ated as a virulence factor of this organism. Therefore, the LPS from a stable virulent isolate, SE6-E21, was compared with that from an avir ulent isolate, SE6-E5. The LPSs were extracted, and the high-molecular -weight (HMW) LPS was separated from the low-molecular-weight (LMW) LP S for both isolates, Both the HMW and LMW LPSs were characterized by g lycosyl composition and linkage analyses, Immunochemical characterizat ion was performed by Western blotting using factor 9 antiserum and usi ng S. typhimurium antiserum which contains factors 1, 4, 5, and 12(2). In addition, the polysaccharides released by mild acid hydrolysis wer e isolated and subjected to hydrolysis by bacteriophage P22, which con tains endorhamnosidase activity, The resulting oligosaccharides were p urified by using Bio-Gel P4 gel permeation chromatography and characte rized by nuclear magnetic resonance spectroscopy, fast atom bombardmen t mass spectrometry (FAB-MS), tandem MS-MS, and matrix-assisted laser desorption time of flight MS, The results show that the HMW LPS O-anti gen polysaccharides from both isolates are comprised of two different repeating units, -(1-->4)-alpha-L-Rhap-(1-->3)-alpha-D-Galp-(1-->]- (s tructure I) and [-->2)- (1-->3)-[alpha-D-Glcp-(1-->4)]alpha-D-Galp-(1- ->]- (structure II), The LMW LPSs from both isolates contains truncate d O-antigen polysaccharide which is comprised of only structure I, In the virulent SE6-E21 isolate, the HMW LPS has a structure I/II ratio o f 1:1, while in the avirulent SE6-E5 isolate, this ratio is 7:1. While the 7:1 ratio represents the published level of glucosylation for S. enteritidis LPS as well as for S. enteritidis LPS purchased from Sigma Chemical Co., the 1:1 ratio found for the virulent SE6-E21 is identic al to the high level of glucosylation reported for S. typhi LPS, Thus, the LPS from the virulent SE6-E21 isolate produces an S. typhi-like L PS, Furthermore, the amount of O-antigen polysaccharide in SE6-E21 was twice that in SE6-E5.