Lipopolysaccharide-associated resistance to killing of yersiniae by complement

Yersinia pestis, Y. pseudotuberculosis, and Y. enterocolitica share ~70 kb low calcium response (Lcr) plasmids encoding virulence factors expressed at 37°C that, except for the adhesin YadA, are repressed by Ca 2+ (Lcr + ). Virulence factors encoded on both the Lcr plasmid and chromosome have been reported to protect yersiniae against complement-dependent killing. In this study, LPS was isolated from yersiniae of serum-sensitive phenotypes (Lcr + and Lcr - Y. enterocolitica and Y. pseudotuberculosis grown at 26°C and Lcr - Y. enterocolitica grown at 37°C) and incorporated into liposomes containing radioactive chromium. These vesicles lysed with release of free 51 Cr in normal but not decomplemented serum. Liposomes prepared from serum-resistant phenotypes (Lcr + and Lcr - Y. pestis grown at 26°C or 37°C, Lcr + and Lcr - Y. pseudotubercu losis grown at 37°C, and Lcr + Y. enterocolitica grown at 37°C) did not undergo complement-dependent lysis. LPS from serum-resistant Y. pestis and Y. pseudotuberculosis was rough as judged by deficiency of O-groups.