Low genetic diversity of Haemophilus influenzae type b compared to nonencapsulated H. influenzae in a population in which H. influenzae is highly endemic

Abstract

Immunization with Haemophilus influenzae type b (Hib) conjugate polysaccharide vaccines has dramatically reduced Hib disease worldwide. As in other populations, nasopharyngeal carriage of Hib declined markedly in Aboriginal infants following vaccination, although carriage has not been entirely eliminated. In this study, we describe the genetic characteristics and the carriage dynamics of longitudinal isolates of Hib, characterized by using several typing methods. In addition, carriage rates of nonencapsulated H. influenzae (NCHi) are high, and concurrent colonization with Hib and NCHi is common; we also observed NCHi isolates which were genetically similar to Hib. There is a continuing need to promote Hib immunization and monitor H. influenzae carriage in populations in which the organism is highly endemic, not least because of the possibility of genetic exchange between Hib and NCHi strains in such populations.

FIG. 1

Example of the IS-bexA deletion in a phylogenetic division I Hib strain with a duplication at cap. The diagonal line indicates the location of the IS-bexA deletion. PCR amplification using primers denoted IF and IR resulted in a strong product of approximately 339 bp which relates to the truncated region and a lighter product (PCR is preferential to smaller products) of 1.2 kb relating to the complete form of the IS1016 bridge region.

FIG. 2

PCR ribotype patterns of representative isolates of H. influenzae (HaeIII digest). Lane 1, Hib MinnA; lane 2, Hib-PRT 1 (608-1); lane 3, NCHi-PRT 1 (855-1); lane 4, Hib-PRT 2 (Hib isolated from a Darwin infant). This photograph was digitized with Deskscan II software and annotated with Corel Photopaint.

FIG. 3

ERIC PCR fingerprinting patterns of H. influenzae. Lanes 1, 2, and 5, Hib-PRT 1/ERIC A; lanes 3, 4, and 6 to 9, Hib-PRT 1/ERIC B; lane 10, NCHi-PRT 1/ERIC D; lane 11, NCHi-PRT 1/ERIC E; lanes 12 and 13, NCHi-PRT 1/ERIC F; lane 14, Hib-PRT 2/ERIC C (Hib isolated from a Darwin infant). The image was digitally acquired by using Bio-Rad GelDoc 1000 and annotated with Corel Draw.

FIG. 4

ApoI PCR ribotype patterns of H. influenzae. Lane 1, NCHi 621-1 (HaeIII PRT 4); lane 2, NCHi 473-22 (HaeIII PRT 3); lane 3, NCHi 413-1 (HaeIII PRT 51); lane 4, NCHi 521-1 (HaeIII PRT 2); lane 5, NCHi 599-4 (HaeIII PRT 17); lane 6, NCHi 273-1 (HaeIII PRT 1); lane 7, NCHi 855-1 (HaeIII PRT 1); lane 8, Hib MinnA (HaeIII PRT 1); lane 9, Hib 608-1 (HaeIII PRT 1). The image was digitally acquired by using Bio-Rad GelDoc 1000 and annotated with Corel Draw.