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

Abstract

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.

The Respiratory Microbiome in Paediatric Chronic Wet Cough: What Is Known and Future Directions

“…Likewise, intranasal administration of Bifidobacterium longum reduced influenza viral load in a mouse model [ 222 ]. Other studies show oropharyngeal H. haemolyticus carriage correlates with reduced NTHi prevalence and density [ 223 ], with anti-NTHi activity also demonstrated in vitro [ 83 ]. Taken together, these data indicate potential therapeutic utility of respiratory-administered probiotics; however, progression of respiratory probiotics into clinical trials first requires improved understanding of the key microbes and metabolites, delivery methods, timing, efficacy in humans, effect duration, safety, and generalisability of use (for example, among children or those with existing chronic lung disease).…”

Heme sequestration by hemophilin from Haemophilus haemolyticus reduces respiratory tract colonization and infection with non-typeable Haemophilus influenzae

“…Importantly, Hpl binds heme in a manner that cannot be utilized by NTHi, thus inhibiting NTHi growth in vitro ( 17 – 20 ). In humans, colonization with Hpl-expressing H. haemolyticus is associated with lower NTHi burdens in the upper airway and a reduced risk of NTHi acquisition, suggesting a beneficial role for Hpl expression ( 21 ). Here, we investigated the hypothesis that H. haemolyticus reduces NTHi burdens in the upper and lower airway in an Hpl-dependent manner and determined whether recombinant Hpl was sufficient for protection against NTHi colonization and lung infection.…”

Bacterial hemophilin homologs and their specific type eleven secretor proteins have conserved roles in heme capture and are diversifying as a family

“…Hemophilin producing strains of H. haemolyticus inhibit the growth of H. influenzae significantly more than non-hemophilin encoding strains in co-cultured media [18] and cell cultures [20]. Additionally, oropharyngeal sampling of human subjects indicates that individuals who carry hemophilin encoding H. haemolyticus are between 2.43 and 2.67 times less likely to carry nontypeable H. influenzae [21]. Conversely, within the opportunistic pathogen A. baumannii, hemophilin can act as a virulence factor by facilitating systemic infection in a murine model [13].…”