PCR FOR CAPSULAR TYPING OF HAEMOPHILUS-INFLUENZAE

A PCR method for the unequivocal assignment of Haemophilus influenzae capsular type (types a to f) was developed. PCR primers were designed from capsule type-specific DNA sequences cloned from the capsular gene cluster of each of the six capsular types. PCR product was amplified only from the capsular type for which the primers were designed. Produ ct was confirmed by using either an internal oligonucleotide or restri ction endonuclease digestion. A total of 172 H. influenzae strains of known capsular type (determined genetically) comprising all capsular t ypes and noncapsulate strains were tested by PCR capsular typing. In a ll cases the PCR capsular type corresponded to the capsular genotype d etermined by restriction fragment length polymorphism analysis of the cap region. When used in conjunction with PCR primers derived from the capsular gene bexA, capsulate, noncapsulate, and capsule-deficient ty pe b mutant strains could be differentiated. PCR capsular typing overc omes the problems of cross-reaction and autoagglutination associated w ith the serotyping of H. influenzae strains. The rapid and unequivocal capsular typing method that is described will be particularly importa nt for typing invasive H. influenzae strains isolated from recipients of H. influenzae type b vaccine.