Duplication of pilus gene complexes of Haemophilus influenzae biogroup aegyptius

Abstract

Brazilian purpuric fever (BPF) is a recently described pediatric septicemia caused by a strain of Haemophilus influenzae biogroup aegyptius. The pilus specified by this bacterium may be important in BPF pathogenesis, enhancing attachment to host tissue. Here, we report the cloning of two haf (for H. influenzae biogroup aegyptius fimbriae) gene clusters from a cosmid library of strain F3031. We sequenced a 6.8-kb segment of the haf1 cluster and identified five genes (hafA to hafE). The predicted protein products, HafA to HafD, are 72, 95, 98, and 90% similar, respectively, to HifA to HifD of the closely related H. influenzae type b pilus. Strikingly, the putative pilus adhesion, HifE, shares only 44% identity with HafE, suggesting that the proteins may differ in receptor specificity. Insertion of a mini-␥␦ transposon in the hafE gene eliminated hemadsorption. The nucleotide sequences of the haf1 and haf2 clusters are more than 99% identical. Using the recently published sequence of the H. influenzae Rd genome, we determined that the haf1 complex lies at a unique position in the chromosome between the pmbA gene and a hypothetical open reading frame, HI1153. The location of the haf2 cluster, inserted between the purE and pepN genes, is analogous to the hif genes on H. influenzae type b. BPF fimbrial phase switching appears to involve slip-strand mispairing of repeated dinucleotides in the pilus promoter. The BPF-associated H. influenzae biogroup aegyptius pilus system generally resembles other H. influenzae, but the possession of a second fimbrial gene cluster, which appears to have arisen by a recent duplication event, and the novel sequence of the HafE adhesin may be significant in the unusual pathogenesis of BPF.

Nucleotide Sequence Analysis of Hypervariable Junctions of Haemophilus influenzae Pilus Gene Clusters

“…3B), direct repeats featuring IDS elements vary in copy number between strains, presumably due to slip-stranded replication (22). A similar process seems to be happening within the pilus cluster between hifA and hifB, where there are 10 directly repeated IDSs in serotype b strain AM30 (23) but only one in Hae strain F3031 (17). The left hif-2 junction is even more variable than the right (Fig.…”

“…The hif-1 and hif-2 clusters of Hae strain F3031 were shown to be more than 99% similar (17); furthermore, sequences immediately flanking the clusters are highly conserved ( Fig. 2 and 3).…”

“…The five hif genes that encode pili have been found at two distinct chromosomal locations (8,14,17,23) (Fig. 1).…”

Haemophilus influenzae : Genetic Variability and Natural Selection To Identify Virulence Factors

“…Recombination events resulting in additional copies of the cap locus generate Hib variants with increased pathogenicity proportional to the number of copies present and the amount of capsule produced (12,23). Because of the presence of a second copy of the hif locus, some H. influenzae biogroup aegyptius strains (including strains isolated from patients with Brazilian purpuric fever) display abundant piliation, reflecting the decreased probability that, at any point in time, both copies of the phase-variable pilus promoters are present in the off orientation (35,37).…”

Fimbrial ghf Gene Cluster of Genital Strains of Haemophilus spp

“…The principal fimbrial gene cluster studied in Hib and NTHi encodes long, thick, and hemagglutination-positive (LKP) fimbriae. The LKP fimbrial gene cluster contains five genes, hifA to hifE, and is regulated by two overlapping and inverted promoters located between hifA and hifB (8,24,31,32). The first promoter initiates the transcription of hifA.…”