Nontypeable Haemophilus influenzae Type IV Pilus Mediates Augmented Adherence to Rhinovirus-Infected Human Airway Epithelial Cells

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

Chronic wet cough for longer than 4 weeks is a hallmark of chronic suppurative lung diseases (CSLD), including protracted bacterial bronchitis (PBB), and bronchiectasis in children. Severe lower respiratory infection early in life is a major risk factor of PBB and paediatric bronchiectasis. In these conditions, failure to clear an underlying endobronchial infection is hypothesised to drive ongoing inflammation and progressive tissue damage that culminates in irreversible bronchiectasis. Historically, the microbiology of paediatric chronic wet cough has been defined by culture-based studies focused on the detection and eradication of specific bacterial pathogens. Various 'omics technologies now allow for a more nuanced investigation of respiratory pathobiology and are enabling development of endotype-based models of care. Recent years have seen substantial advances in defining respiratory endotypes among adults with CSLD; however, less is understood about diseases affecting children. In this review, we explore the current understanding of the airway microbiome among children with chronic wet cough related to the PBB-bronchiectasis diagnostic continuum. We explore concepts emerging from the gut-lung axis and multi-omic studies that are expected to influence PBB and bronchiectasis endotyping efforts. We also consider how our evolving understanding of the airway microbiome is translating to new approaches in chronic wet cough diagnostics and treatments.

Biofilm aggregates and the host airway-microbial interface

Biofilms are multicellular microbial aggregates that can be associated with host mucosal epithelia in the airway, gut, and genitourinary tract. The host environment plays a critical role in the establishment of these microbial communities in both health and disease. These host mucosal microenvironments however are distinct histologically, functionally, and regarding nutrient availability. This review discusses the specific mucosal epithelial microenvironments lining the airway, focusing on: i) biofilms in the human respiratory tract and the unique airway microenvironments that make it exquisitely suited to defend against infection, and ii) how airway pathophysiology and dysfunctional barrier/clearance mechanisms due to genetic mutations, damage, and inflammation contribute to biofilm infections. The host cellular responses to infection that contribute to resolution or exacerbation, and insights about evaluating and therapeutically targeting airway-associated biofilm infections are briefly discussed. Since so many studies have focused on Pseudomonas aeruginosa in the context of cystic fibrosis (CF) or on Haemophilus influenzae in the context of upper and lower respiratory diseases, these bacteria are used as examples. However, there are notable differences in diseased airway microenvironments and the unique pathophysiology specific to the bacterial pathogens themselves.

Nontypeable Haemophilus influenzae newly released (NRel) from biofilms by antibody-mediated dispersal versus antibody-mediated disruption are phenotypically distinct

Biofilms contribute significantly to the chronicity and recurrence of bacterial diseases due to the fact that biofilm-resident bacteria are highly recalcitrant to killing by host immune effectors and antibiotics. Thus, antibody-mediated release of bacteria from biofilm residence into the surrounding milieu supports a powerful strategy to resolve otherwise difficult-to-treat biofilm-associated diseases. In our prior work, we revealed that antibodies directed against two unique determinants of nontypeable Haemophilus influenzae (NTHI) [e.g. the Type IV pilus (T4P) or a bacterial DNABII DNA-binding protein, a species-independent target that provides structural integrity to bacterial biofilms] release biofilm-resident bacteria via discrete mechanisms. Herein, we now show that the phenotype of the resultant newly released (or NRel) NTHI is dependent upon the specific mechanism of release. We used flow cytometry, proteomic profiles, and targeted transcriptomics to demonstrate that the two NRel populations were significantly different not only from planktonically grown NTHI, but importantly, from each other despite genetic identity. Moreover, each NRel population had a distinct, significantly increased susceptibility to killing by either a sulfonamide or β-lactam antibiotic compared to planktonic NTHI, an observation consistent with their individual proteomes and further supported by relative differences in targeted gene expression. The distinct phenotypes of NTHI released from biofilms by antibodies directed against specific epitopes of T4P or DNABII binding proteins provide new opportunities to develop targeted therapeutic strategies for biofilm eradication and disease resolution.