Background: Nontypeable Haemophilus influenzae (NTHi) is a major respiratory pathogen that initiates infection by colonising the pharynx. Strategies that interfere with this interaction may therefore have a clinically significant impact on the ability of NTHi to cause disease. We have previously shown that strains of the commensal bacterium Haemophilus haemolyticus (Hh) that produce a novel haem-binding protein, haemophilin (Hpl), can prevent NTHi growth and interactions with host cells in vitro. We hypothesized that natural pharyngeal carriage of Hh strains with the hpl open reading frame (Hh-hpl+) would be associated with a lower prevalence and/or density of NTHi colonisation in healthy individuals.
Methods: Oropharyngeal swabs were collected from 257 healthy adults in Australia between 2018 and 2019. Real-time PCR was used to quantitatively compare the oropharyngeal carriage load of NTHi and Hh populations with the Hh-hpl+ or Hh-hpl- genotype. The likelihood of acquiring/maintaining NTHi colonisation status over a 2–6-month period was assessed in individuals that carried either Hh-hpl- (n=25) or Hh-hpl+ (n=25).
Results: A propensity for lower Hh and Hh-hpl+ carriage, and higher NTHi carriage was observed among elderly participants (>65 years), compared to the adult (18-65 years) age group. Compared to carriage of Hh-hpl- strains, adult and elderly participants that were colonised with Hh-hpl+ were 2.43 times (95% CI, 1.95-2.61; p= < 0.0001), or 2.67 times (95% CI, 2.63-2.70; p= 0.0036) less likely to carry NTHi in their oropharynx, respectively. Colonisation with high densities of Hh-hpl+ correlated with low NTHi carriage load, and 2.63 times (95% CI, 2.56-2.70, p = 0.0112) lower likelihood of acquiring/maintaining NTHi colonisation status between visits.
Conclusions: In summary, carriage of Hh-hpl+ was associated with a significantly lower proportionate density and prevalence of concurrent NTHi carriage, and long-term maintenance or acquisition of NTHi colonisation status. Together with supporting in vitro studies, these results encourage further investigation into the potential use of Hh-hpl+ as a respiratory probiotic candidate for the prevention of NTHi infection.