Abstract
Haemophilus ducreyi, the etiologic agent of chancroid, has been previously reported to show genetic variance in several key virulence factors, placing strains of the bacterium into two genetically distinct classes. Recent studies done in yaws-endemic areas of the South Pacific have shown that H. ducreyi is also a major cause of cutaneous limb ulcers (CLU) that are not sexually transmitted. To genetically assess CLU strains relative to the previously described class I, class II phylogenetic hierarchy, we examined nucleotide sequence diversity at 11 H. ducreyi loci, including virulence and housekeeping genes, which encompass approximately 1% of the H. ducreyi genome. Sequences for all 11 loci indicated that strains collected from leg ulcers exhibit DNA sequences homologous to class I strains of H. ducreyi. However, sequences for 3 loci, including a hemoglobin receptor (hgbA), serum resistance protein (dsrA), and a collagen adhesin (ncaA) contained informative amounts of variation. Phylogenetic analyses suggest that these non-sexually transmitted strains of H. ducreyi comprise a sub-clonal population within class I strains of H. ducreyi. Molecular dating suggests that CLU strains are the most recently developed, having diverged approximately 0.355 million years ago, fourteen times more recently than the class I/class II divergence. The CLU strains' divergence falls after the divergence of humans from chimpanzees, making it the first known H. ducreyi divergence event directly influenced by the selective pressures accompanying human hosts.
Highlights
Haemophilus ducreyi is a Gram-negative coccobacillus in the polyphyletic family Pasteurellaceae, and is the etiologic agent of the sexually transmitted infection chancroid, a genital ulcer disease [1]
Four genes previously used to distinguish class I and II had very limited variation even between class I and II [17], and were excluded from this analysis. In place of these four genes, we examined four additional loci, cpxR, ompA2, dltA, and 16s rDNA, to better distinguish the cutaneous limb ulcers (CLU) strains from class I and class II H. ducreyi
We describe genotyping of cutaneous leg ulcer H. ducreyi strains using an Multi Locus Sequence Analysis (MLSA) approach that provides information for the genetic basis of the population structure (Table 2)
Summary
Haemophilus ducreyi is a Gram-negative coccobacillus in the polyphyletic family Pasteurellaceae, and is the etiologic agent of the sexually transmitted infection chancroid, a genital ulcer disease [1]. H. ducreyi has historically only been known to cause genital ulcer infections as chancroid is transmitted via micro-abrasions developed during sexual intercourse [1]. No additional reports of non-genital H. ducreyi infection were reported until 2007, when H. ducreyi was confirmed to be the etiologic agent of cutaneous limb ulcers (CLU) present in three children ranging between 6–9 years of age via phenotypic testing on cultures and by 16S rDNA sequencing [7]. These cases occurred after travel to the South Pacific, as each child had recently visited Samoa. Chronic limb ulcers caused by H. ducreyi are not limited to children [9]. [10]
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