Clinical and veterinary isolates of Salmonella enterica serovar enteritidis defective in lipopolysaccharide O-chain polymerization

Twelve human and chicken isolates of Salmonella enterica serovar Enteritidi s belonging to phage types 4, 8, 13a, and 23 were characterized for variabi lity in lipopolysaccharide (LPS) composition. Isolates were differentiated into two groups, i.e., those that lacked immunoreactive O-chain, termed rou gh isolates, and those that had immunoreactive O-chain, termed smooth isola tes. Isolates within these groups could be further differentiated by LPS co mpositional differences as detected by gel electrophoresis and gas liquid c hromatography of samples extracted with water, which yielded significantly more LPS in comparison to phenol-chloroform extraction. The rough isolates were of two types, the O-antigen synthesis mutants and the O-antigen polyme rization (wzy) mutants. Smooth isolates were also of two types, one produci ng low-molecular-weight (LMW) LPS and the other producing high-molecular-we ight (HMW) LPS. To determine the genetic basis for the O-chain variability of the smooth isolates, we analyzed the effects of a null mutation in the O -chain length determinant gene, wzz (cld) of serovar Typhimurium. This muta tion results in a loss of HMW LPS; however, the LMW LPS of this mutant was longer and more glucosylated than that from clinical isolates of serovar En teritidis, Cluster analysis of these data and of those from two previously characterized isogenic strains of serovar Enteritidis that had different vi rulence attributes indicated that glucosylation of HMW LPS (via oafR functi on) is variable and results in two types of HMW structures, one that is hig hly glucosylated and one that is minimally glucosylated. These results stro ngly indicate that naturally occurring variability in wzy, wzz, and oafR fu nction can be used to subtype isolates of serovar Enteritidis during epidem iological investigations.