Sialylation of lipopolysaccharide and loss of absorption of bactericidal antibody during conversion of gonococci to serum resistance by cytidine 5'-monophospho-N-acetyl neuraminic acid.

Changes in lipopolysaccharide (LPS) which occur when serum susceptible gonococci are converted to resistance by incubation with cytidine 5'-monophospho-N-acetyl neuraminic acid (CMP-NANA) have been investigated. Transfer of radioactivity to bacterial LPS from CMP-NANA labelled with 14C in the NANA moiety was detected by fluorography following lysis, proteinase K digestion and SDS-PAGE. Incorporation of radioactivity was inhibited by cytidine 5'-monophosphate (CMP). Both the radioactivity of the LPS and the resistance of gonococci to fresh human serum were largely lost after incubation with neuraminidase. No evidence was obtained to suggest that CMP-NANA is an inducer of new protein synthesis as well as a substrate for the sialylation of LPS. Little radioactivity was incorporated into components other than LPS. Sialylated, serum resistant gonococci were less able than serum susceptible gonococci to absorb the bactericidal activity of fresh human serum. Hence, we conclude that serum resistance conferred on gonococci by CMP-NANA is due to transfer of sialyl groups to surface LPS sites and this inhibits their reaction with bactericidal antibody in human serum.