Dataset Information

Complete sequence of the cap locus of Haemophilus influenzae serotype b and nonencapsulated b capsule-negative variants.

ABSTRACT: The complete capsule (cap) loci from three Haemophilus influenzae strains, one serotype b (Hib) and two nonencapsulated b capsule-negative variants, were sequenced. Two new open reading frames, hcsA and hcsB, were identified in region III and thought to be involved in postpolymerization modification of the capsule. The location of the cap locus in the Haemophilus influenzae chromosome was identified within section 97 of the Rd genome (chromosomal coordinates 1074542 to 1086327) and found to be the same for the Hib and two Hib(-) strains as well as some other encapsulated division I H. influenzae strains.

SUBMITTER: Satola SW

PROVIDER: S-EPMC155767 | biostudies-literature | 2003 Jun

REPOSITORIES: biostudies-literature

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Complete sequence of the cap locus of Haemophilus influenzae serotype b and nonencapsulated b capsule-negative variants.

Satola Sarah W SW Schirmer Patricia L PL Farley Monica M MM

Infection and immunity 20030601 6

The complete capsule (cap) loci from three Haemophilus influenzae strains, one serotype b (Hib) and two nonencapsulated b capsule-negative variants, were sequenced. Two new open reading frames, hcsA and hcsB, were identified in region III and thought to be involved in postpolymerization modification of the capsule. The location of the cap locus in the Haemophilus influenzae chromosome was identified within section 97 of the Rd genome (chromosomal coordinates 1074542 to 1086327) and found to be t ...[more]

PMID: 12761153

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Project description:The occurrence of fimbria gene clusters in nonencapsulated Haemophilus influenzae strains from chronic bronchitis patients (n = 58), patients with acute otitis media (n = 13), and healthy carriers (n = 12) was determined by DNA hybridization and PCR, based on sequences of fimbriate H. influenzae type b. Although an average of 18% of all nonencapsulated strains had a fimbria gene cluster consisting of hifA to hifE inserted in the chromosome between purE and pepN, differences in the frequency of fimbria cluster-positive strains were observed, depending on the source of isolates. The compositions of the fimbria gene clusters of seven strains from chronic bronchitis patients and one strain from an otitis media patient were analyzed in more detail. After enrichment for fimbria expression, the promoter of the gene cluster contained 10 TA repeats (n = 2), leading to optimal positioning between the -10 and -35 promoter regions. The promoter regions of five fimbria-negative strains were sequenced; four were found to have nine TA repeats, and one had only four TA repeats. The protein sequence of three ganglioside GM1-specific HifA adhesins consisted of conserved regions intermingled with regions of sequence diversity. hifA appeared to be flanked by intergenic regions that varied between strains and contained both direct and inverted DNA repeats. Since noncoding DNA between hifA and purE has not been found in H. influenzae type b, these DNA sequences are probably not essential for fimbria expression. An analysis of strains lacking the gene cluster revealed the presence of similar sequences in 13 of 15 strains from chronic bronchitis patients, 5 of 5 strains from otitis media patients, and 3 of 5 strains from healthy carriers. The lengths of these intergenic regions were the same for multiple isolates of strains obtained during persistent infections. The presence or absence and the composition of the fimbria gene cluster and other sequences between the flanking genes purE and pepN suggest that the fimbria gene cluster was originally contained on a mobile element.

Project description:BackgroundDespite nearly complete vaccine coverage, a small number of fully vaccinated children in the Netherlands have experienced invasive disease caused by Haemophilus influenzae serotype b (Hib). This increase started in 2002, nine years after the introduction of nationwide vaccination in the Netherlands. The capsular polysaccharide of Hib is used as a conjugate vaccine to protect against Hib disease. To evaluate the possible rise of escape variants, explaining the increased number of vaccine failures we analyzed the composition of the capsular genes and the expressed polysaccharide of Dutch Hib strains collected before and after the introduction of Hib vaccination.ResultsThe DNA sequences of the complete capsular gene clusters of 9 Dutch Hib strains were assessed and two variants, designated type I and type II were found. The two variants displayed considerable sequence divergence in the hcsA and hcsB genes, involved in transport of capsular polysaccharide to the cell surface. Application of hcsA type specific PCRs on 670 Hib strains collected from Dutch patients with invasive Hib disease showed that 5% of the strains collected before 1996 were type II. No endogenous type II Hib strains were isolated after 1995 and all type II strains were isolated from 0-4 year old, non-vaccinated children only. Analysis of a worldwide collection of Hib strains from the pre-vaccination era revealed considerable geographic differences in the distribution of the type I and type II strains with up to 73% of type II strains in the USA. NMR analysis of type I and type II capsule polysaccharides did not reveal structural differences. However, type I strains were shown to produce twice as much surface bound capsular polysaccharide.ConclusionType II strains were only isolated during the pre-vaccination era from young, non-vaccinated individuals and displayed a lower expression of capsular polysaccharide than type I strains. The higher polysaccharide expression may have provided a selective advantage for type I strains resulting in the rapid elimination of type II from the Dutch Hib population after introduction of nationwide Hib vaccination. However, this phenomenon does not explain the increase in the number of Hib vaccine failures in the Netherlands.

Dataset Information

Complete sequence of the cap locus of Haemophilus influenzae serotype b and nonencapsulated b capsule-negative variants.

Publications

Complete sequence of the cap locus of Haemophilus influenzae serotype b and nonencapsulated b capsule-negative variants.

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