Identification of a gene essential for O-acetylation of the Staphylococcus aureus type 5 capsular polysaccharide

The Staphylococcus aureus serotype 5 capsular polysaccharide (CP5) has a trisaccharide repeating unit of (-4)-3-O-Ac-beta-D-ManNAcAp-(1 --> 4)-alpha-L-FucNAcp-(1-->3)-beta-D-FucNAcp-(1-->). Tn918 mutagenesis of strain Reynolds yielded a mutant that produced wild-type levels of O-deacetylated CP5. The site and orientation of the single transposon insertion in mutant JL232 were determined by analysis of Southern blots and amplification of DNA flanking the transposon. DNA sequencing revealed that Tn918 was inserted within an open reading frame of 627 bp. The predicted amino acid sequence encodes a protein of approximately 26 kDa with homology to members of the NodL-LacA-CysE family of bacterial acetyltransferases. Southern blot analysis showed that genes similar to cap5H were present only in strains of S. aureus belonging to capsular serotypes 2, 4 and 5. In an in vitro assay, the parental strain was more resistant to opsonophagocytic killing than the mutant strain. In a mouse model of staphylococcal infection, the parental strain was able to seed the bloodstream from the peritoneal cavity and colonize the kidneys more efficiently than the O-deacetylated mutant. When cap5H was provided to the mutant in trans, it fully restored CP5 O-acetylation. The virulence of the complemented mutant strain closely approximated that of the parental strain.