Inorganic particulate matter modulates non-typeable Haemophilus influenzae growth: a link between chronic bacterial infection and geogenic particles

Abstract

Australian Aboriginal populations have unacceptably high rates of bronchiectasis. This disease burden is associated with high rates of detection of pathogenic bacteria; particularly Nontypeable Haemophilus influenzae (NTHi). While there is evidence to suggest that exposure to inorganic particulate matter (PM) is associated with worse respiratory infections, no studies have considered the direct effect of this PM on bacterial growth. Nine clinical isolates of pathogenic NTHi were used for this study. Isolates were exposed to two common iron oxides, haematite (Fe2O3) or magnetite (Fe3O4), or quartz (SiO2), as the main constituents of environmental inorganic PM. NTHi isolates were exposed to PM with varying levels of heme to identify whether the response to PM was altered by iron availability. The maximal rate of growth and maximum supported growth were assessed. We observed that inorganic PM was able to modify the maximal growth of selected NTHi isolates. Magnetite and quartz were able to increase maximal growth while haematite could both increase and suppress the maximal growth. However, these effects varied depending on iron availability and on the bacterial isolate. Our data suggests that inorganic PM may directly alter the growth of pathogenic NTHi. This observation may partly explain the link between exposure to high levels of crustal PM and chronic bacterial infection in Australian Aboriginals.

Geogenic Particles Induce Bronchial Susceptibility to NTHi

“…NTHi are fastidious heme auxotrophs. This is the second line of evidence from our group that has suggested these bacteria may be able to bene t from environmental iron (Williams et al, 2020). Combined with our functional data, it suggests that these differences in genes are not critical to haematite-induced invasion but exacerbate invasion and could be linked to worse infection.…”