CHARACTERIZATION OF LIPOPOLYSACCHARIDE HETEROGENEITY IN SALMONELLA-ENTERITIDIS BY AN IMPROVED GEL-ELECTROPHORESIS METHOD

Salmonella enteritidis field isolates of different phage types and pat hogenicities were assessed for changes in lipopolysaccharide (LPS) str ucture, using an improved method of polyacrylamide gel electrophoresis (PAGE) that revealed the same degree of structural detail as mass spe ctroscopy, The method allowed characterization of an LPS chemotype tha t may be associated, regardless of phage type, with increased virulenc e of S, enteritidis, The virulent variant SE6-E21, which efficiently c ontaminates eggs and yields high numbers of organisms from chick splee ns, had an O-antigen/core ratio of 2.8, as determined from gels by den sitometry, and 1.67 mu g of mannose per mu g of 2-keto-3-deoxy-octulos onic acid (KDO), while the avirulent variant SE6-E5 had O-antigen/core ratios of 1.2 and 1.00, The association between O antigen and virulen ce was also seen on analysis of five new field isolates, One of the ne w field isolates generated a mixed population of smooth and semismooth variants in agreement with its mixed virulence in chicks, When LPS wa s purified from large-volume cultures, only the most virulent isolate yielded high amounts of O antigen (1.6 mu g of mannose per mu g of KDO ), while the other isolates had ratios characteristic of semismooth va riants (less than or equal to 1.0 mu g of mannose per mu g of KDO), in cluding the isolate of mixed virulence, These results indicate that th e improved PAGE method might provide a rapid, sensitive, in vitro asse ssment of field isolate virulence prior to the performance of definiti ve infectivity trials.