THE ELUCIDATION OF NOVEL CAPSULAR GENOTYPES OF HAEMOPHILUS-INFLUENZAETYPE-B WITH THE POLYMERASE CHAIN-REACTION

Molecular characterisation is an important pre-requisite for post-vacc ine studies of Haemophilus influenzae type b (Hib). Three capsular gen otyping patterns, b(S), b(G) and b(V), have been described in the majo r phylogenetic lineage of Hib. However, in a recent series of prospect ive studies, three new hybridisation patterns were observed among 425 strains of Hib. Four pairs of polymerase chain reaction (PCR) primers were used to identify the capsular gene (cap) structure of these Hib s trains. This showed that the strains possessed simple DNA re-arrangeme nts. In two instances a change in restriction enzyme recognition site was the most likely cause of the new hybridisation pattern. The third strain possessed a cap b locus consisting of intact tandem repeats of cap b in a b(S) background. It was reasoned that a similar cap b locus would not be readily recognised by hybridisation in a b(G) background , and b(G) strains were therefore characterised by the PCR method. Thi s showed one of 35 b(G) strains to possess a cap locus with intact tan dem repeat copies of cap b. The novel capsular genotypes described her e are rare, but can be detected rapidly and accurately by a combinatio n of PCR and capsular genotyping hybridisation patterns.