Access to highly specialized growth substrates and production of epithelial immunomodulatory metabolites determine survival of Haemophilus influenzae in human airway epithelial cells.

Jennifer Hosmer,Rabeb Dhouib,Anna Henningham,Marufa Nasreen,Ulrike Kappler,Emmanuelle Fantino,Horst Joachim Schirra,Alastair G Mcewan,Peter Sly,Ama-Tawiah Essilfie,William Navarre

doi:10.1371/journal.ppat.1010209

Abstract

Haemophilus influenzae (Hi) infections are associated with recurring acute exacerbations of chronic respiratory diseases in children and adults including otitis media, pneumonia, chronic obstructive pulmonary disease and asthma. Here, we show that persistence and recurrence of Hi infections are closely linked to Hi metabolic properties, where preferred growth substrates are aligned to the metabolome of human airway epithelial surfaces and include lactate, pentoses, and nucleosides, but not glucose that is typically used for studies of Hi growth in vitro. Enzymatic and physiological investigations revealed that utilization of lactate, the preferred Hi carbon source, required the LldD L-lactate dehydrogenase (conservation: 98.8% of strains), but not the two redox-balancing D-lactate dehydrogenases Dld and LdhA. Utilization of preferred substrates was directly linked to Hi infection and persistence. When unable to utilize L-lactate or forced to rely on salvaged guanine, Hi showed reduced extra- and intra-cellular persistence in a murine model of lung infection and in primary normal human nasal epithelia, with up to 3000-fold attenuation observed in competitive infections. In contrast, D-lactate dehydrogenase mutants only showed a very slight reduction compared to the wild-type strain. Interestingly, acetate, the major Hi metabolic end-product, had anti-inflammatory effects on cultured human tissue cells in the presence of live but not heat-killed Hi, suggesting that metabolic endproducts also influence HI-host interactions. Our work provides significant new insights into the critical role of metabolism for Hi persistence in contact with host cells and reveals for the first time the immunomodulatory potential of Hi metabolites.

Highlights

The success of Haemophilus influenzae (Hi) as a pathobiont is directly linked to its remarkable ability to persist in the human host and to access different epithelial niches
We have shown that Hi metabolism is adapted to the human respiratory tract, and access to preferred growth substrates, which included L-lactate, is required for Hi long-term persistence in primary human epithelia, including intracellular colonization of the host cells
The role of metabolism for host interactions was not limited to growth substrates but extended to Hi metabolic endproducts where we were able to link the immunometabolite acetate to a reduction of the host immune response to Hi infection

Summary

Introduction

The success of Haemophilus influenzae (Hi) as a pathobiont is directly linked to its remarkable ability to persist in the human host and to access different epithelial niches. The ability of various bacterial pathogens to thrive intracellularly during infection of human tissues often correlates with increased persistence of infections and reduces the efficacy of antimicrobial therapy. Increasing evidence suggests that in addition to colonizing human epithelia extracellularly, Hi is able to enter into epithelial cells and survive intracellularly, including in resected respiratory tissues such as adenoids [14–16]. While uptake of NTHi into tissue cells has been linked to micropinocytosis and different host-cell receptors such as β-glucan receptor and platelet-activating factor (PAF) [19,21–23], there is currently no information about metabolic processes that enable Hi persistence in the cytosol of infected human cells. The links between Hi metabolic activities and colonization of specific cellular niches are only beginning to be understood

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Conclusion