Oropharyngeal Carriage of hpl-Containing Haemophilus haemolyticus Predicts Lower Prevalence and Density of NTHi Colonisation in Healthy Adults

Nontypeable Haemophilus influenzae (NTHi) is a major respiratory pathogen that initiates infection by colonising the upper airways. 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, 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. 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 two- to six-month period was assessed in individuals that carried either Hh-hpl(−) (n = 25) or Hh-hpl(+) (n = 25). Compared to carriage of Hh-hpl(−) strains, adult (18–65 years) and elderly (>65 years) participants that were colonised with Hh-hpl(+) were 2.43 or 2.67 times less likely to carry NTHi in their oropharynx, respectively. Colonisation with high densities of Hh-hpl(+) correlated with a low NTHi carriage load and a 2.63 times lower likelihood of acquiring/maintaining NTHi colonisation status between visits. 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.