The haem–haemopexin utilization gene cluster (hxuCBA) as a virulence factor of Haemophilus influenzae

Abstract

Haemophilus influenzae has an absolute growth requirement for a porphyrin source, which can be supplied in vitro by haem, haemoglobin, or the haemoglobin-haptoglobin, haem-haemopexin and haem-albumin complexes. Utilization of the haem-haemopexin complex is known to be mediated by the products of the hxuCBA gene cluster. It was demonstrated that hxuC, but not hxuA or hxuB, is also essential for the utilization of haem from haem-albumin complexes. Mutants of the type b strain E1a lacking genes in the hxuCBA gene cluster were examined for their ability to cause bacteraemia in rat models of invasive disease. In 5-day-old rats, mutants in the hxuCBA genes yielded a significantly reduced bacteraemic titre compared to the wild-type strain. In addition, 5-day-old rats infected with the hxuCBA mutant strains exhibited significantly improved survival rates compared to those infected with the wild-type strain. Mutations in the haemoglobin/haemoglobinhaptoglobin-binding protein genes (hgps), either alone or in combination with the hxuCBA mutations, had no impact on virulence in 5-day-old rats. In 30-day-old rats infected with either the hxuCBA mutants or the wild-type strains, there was no significant difference in the ability to establish bacteraemia although bacterial titres were lower in rats infected with the hxuCBA mutants than in those infected with the wild-type strain. These age-related differences in the impact of mutations in the hxuCBA gene cluster may be related to changes in levels of host haem-binding proteins during development of the rat.

Lipoprotein e (P4) of Haemophilus influenzae: role in heme utilization and pathogenesis

“…These proteins are essential for the utilization of hemoglobin-haptoglobin [9] and the age-related difference in virulence could be explained by hemoglobin-haptoglobin complexes becoming the predominant available heme source in 30-day old rats [14]. We have also recently reported age-related differences in virulence when comparing a type b strain with a mutant in the heme-hemopexin utilization genes (hxuCBA) [10].…”

“…Stock solutions were prepared as previously described [9,10]. Rabbit hemopexin was prepared as described previously [11].…”

“…A rat model was used to assess bacteremia in both 5-day old and 30-day old rats as previously described [10,11,14]. Specified pathogen free timed-pregnant Sprague-Dawley rats were received five days prior to parturition.…”

A Novel Zinc Binding System, ZevAB, Is Critical for Survival of Nontypeable Haemophilus influenzae in a Murine Lung Infection Model

“…Interestingly, several potential DsbA-dependent proteins that were not required in the lung model as determined by HITS are important for H. influenzae pathogenesis in other sites of infection. For example, the hemopexin utilization protein HxuA has been shown to be required for wild-type bacteremic levels in an infant rat model of H. influenzae type B infection (45), and the outer membrane protein P5 (OmpA) is required for virulence of NTHI in a chinchilla model of otitis media (62). This suggests that examination of the requirement for DsbA substrates in other H. influenzae infection models is likely to reveal additional mechanisms involved in pathogenesis.…”

Characterization of the Haemophilus influenzae tehB gene and its role in virulence

“…Mutant genes with subtle effects on virulence, such as those with overlapping/redundant functions (e.g. genes involved Fe/Hm acquisition), often exhibit a significantly reduced ability to produce and sustain bacteraemia in weanling rats compared to infant rats (Seale et al, 2006;Morton et al, 2007aMorton et al, , b, 2009. For this reason we assessed the impact on virulence of the tehB deletion in both infant rats (5 days old) and weanling rats (30 days old) (Fig.…”