PATHOGENICITY IN ISOLATES OF SALMONELLA-ENTERICA SEROTYPE ENTERITIDISPT4 WHICH DIFFER IN RPOS EXPRESSION - EFFECTS OF GROWTH-PHASE AND LOW-TEMPERATURE

Experiments with 2 wild type isolates of Salmonella enterica serotype Enteritidis PT4, which differed in RpoS expression, tolerance to certa in hostile environments and pathogenicity, found that changes in in vi tro acid, heat, or peroxide tolerance had no effect on the ability of the isolates to multiply in the spleens of C57/BL7/J mice infected ora lly. Thus, with the pathogenic RpoS-positive isolate, the infectivity of log phase chilled cells, which are profoundly acid-sensitive, was t he same as that of non-chilled stationary phase cells which are acid-t olerant. Similarity the infectivity of the RpoS-negative, sensitive is olate, was not enhanced by increases in any tolerance. The ability to survive on surfaces, like infectivity, was also largely unaffected by either growth phase or cold exposure. These two attributes may thus be related and, given that the pathogenic PT4 isolate is capable of prol onged survival and the nonpathogenic isolate survives poorly, survival could serve as a potential marker of pathogenicity. Although the path ogenicity of the two isolates was very different, they showed an almos t identical increase in acid tolerance following culture at pH 4.0 for up to 60 min.