Methods: The goals of this study were to: 1) Investigate the role of genes implicated in capsule assembly and export, 2) Determine the capsule diversity of colonizing and invasive isolates through identification of the genetic determinants of capsule synthesis, and 3) Investigate an association between capsule composition and infection site of isolation. The capsule assembly/export genes lipA, lipB, and ctrABCD were all present in a set of clinical K. kingae isolates chosen to reflect different putative capsule types and clinical phenotypes. Interestingly, lipA, lipB, and ctrABCD were located at different loci in the genome without adjacent capsule synthesis genes, which is atypical for bacteria that utilize similar assembly and export machinery for capsule surface localization.
Results: Through a mariner mutagenesis screen in prototype strain 269-492, we identified a putative GalNAc glycosyltransferase gene (gly) necessary for encapsulation that was present in 47% of isolates and was flanked by genes with no putative function in capsule synthesis. Sequencing of the region between the flanking genes in strains lacking the strain 269-492 gly gene revealed a locus encoding either a predicted GlcNAC-transferase (with 2 other hypothetical genes) or two haloacid dehydrogenases (with 1 hypothetical gene). Capsule composition analysis established that these 3 loci were associated with capsule compositions consisting of: 1) Kdo and GalNAc, 2) Kdo and GlcNAc, or 3) Kdo and ribose.
Conclusion: No association was identified between colonizing or invasive strains and a particular capsule type. K. kingae isolates can be separated into three subgroups based on their polysaccharide capsule and the presence of one of three associated capsule synthesis loci. This study has identified novel bacterial capsule types and genetic requirements for K. kingae capsule biogenesis and will inform future vaccine development.
P. Seed, None
J. W. St. Geme III, None