O-Acetylation status of the capsular polysaccharides of serogroup Y and W135 meningococci isolated in the UK.

At a time when tetravalent conjugate vaccines for meningococcal serogroups A/C/Y/W135 are being formulated the O-acetylation status of their respective capsular polysaccharides has not previously been studied in the UK for all components. Although this has been elucidated for serogroup C, little is known about the O-acetylation status of serogroups W135 and Y. Meningococcal serogroup W135 (n=181) and Y (n=90) isolates submitted to the PHLS Meningococcal Reference Unit in 1996, 2000 and 2001 were investigated for O-acetylation capsular status by dot blot assay. Eight per cent of W135 and 79% of Y isolates respectively were found to be O-acetylated with a similar distribution found in both carrier and case isolates. An increase in O-acetylated W135 isolates was noted between 2000 (0%) and 2001 (21%) which was not due to the introduction of the Hajj associated W135 (ET 37 complex; serosubtype P1.5,2) isolates, all of which were de-O-acetylated. Although the biological relevance of O-acetylation status is unknown for these serogroups, an understanding of O-acetylation status of the respective polysaccharides may provide useful insights into the optimal vaccine formulation.