The roles of epithelial cell contact, respiratory bacterial interactions and phosphorylcholine in promoting biofilm formation by Streptococcus pneumoniae and nontypeable Haemophilus influenzae

Haemophilus influenzae and pneumococci: Co-colonization, interactions, cooperation and competition

Nontypeable Haemophilus influenzae (NTHi) and Streptococcus pneumoniae (pneumococcus) are pathobionts that share common environmental niches within the upper respiratory tract. They can form part of the resident upper airway microbiota, but under certain environmental circumstances become pathogenic and induce disease. In children, both organisms have a considerable impact on the healthcare system, commonly causing acute otitis media and pneumonia. They are also associated with chronic biofilm-mediated respiratory infections, such as persistent middle ear effusions and chronic suppurative otitis media, and in the lower airways with protracted bacterial bronchitis and bronchiectasis. Consequently, both organisms are responsible for large numbers of antibiotic prescriptions and substantial healthcare costs. The complex relationship between NTHi and pneumococcal co-interaction during colonization, infection and biofilm formation is poorly understood and a greater understanding is needed to facilitate development of future therapies, and novel interventions and prevention strategies. Co-infections with both bacteria can result in more severe disease, with disease severity likely mediated by their ability to cooperate in some in vivo niches. However, this relationship is not always straightforward, as under certain conditions, these two bacteria compete rather than cooperate. Current opinion supports developing a vaccine targeting NTHi strains, as well as a combined vaccine targeting both NTHi and pneumococci to decrease the respiratory disease burden in young children. This review summarizes our current knowledge of the interactions between NTHi and pneumococci and speculates on the future directions of research to understand how these bacteria co-exist and how to better prevent and treat NTHi and pneumococcal infection.

The Role of Non-Typeable Haemophilus influenzae Biofilms in Chronic Obstructive Pulmonary Disease

Non-typeable Haemophilus influenzae (NTHi) is an ubiquitous commensal-turned-pathogen that colonises the respiratory mucosa in airways diseases including Chronic Obstructive Pulmonary Disease (COPD). COPD is a progressive inflammatory syndrome of the lungs, encompassing chronic bronchitis that is characterised by mucus hypersecretion and impaired mucociliary clearance and creates a static, protective, humid, and nutrient-rich environment, with dysregulated mucosal immunity; a favourable environment for NTHi colonisation. Several recent large COPD cohort studies have reported NTHi as a significant and recurrent aetiological pathogen in acute exacerbations of COPD. NTHi proliferation has been associated with increased hospitalisation, disease severity, morbidity and significant lung microbiome shifts. However, some cohorts with patients at different severities of COPD do not report that NTHi is a significant aetiological pathogen in their COPD patients, indicating other obligate pathogens including Moraxella catarrhalis, Streptococcus pneumoniae and Pseudomonas aeruginosa as the cause. NTHi is an ubiquitous organism across healthy non-smokers, healthy smokers and COPD patients from childhood to adulthood, but it currently remains unclear why NTHi becomes pathogenic in only some cohorts of COPD patients, and what behaviours, interactions and adaptations are driving this susceptibility. There is emerging evidence that biofilm-phase NTHi may play a significant role in COPD. NTHi displays many hallmarks of the biofilm lifestyle and expresses key biofilm formation-promoting genes. These include the autoinducer-mediated quorum sensing system, epithelial- and mucus-binding adhesins and expression of a protective, self-produced polymeric substance matrix. These NTHi biofilms exhibit extreme tolerance to antimicrobial treatments and the immune system as well as expressing synergistic interspecific interactions with other lung pathogens including S. pneumoniae and M. catarrhalis. Whilst the majority of our understanding surrounding NTHi as a biofilm arises from otitis media or in-vitro bacterial monoculture models, the role of NTHi biofilms in the COPD lung is now being studied. This review explores the evidence for the existence of NTHi biofilms and their impact in the COPD lung. Understanding the nature of chronic and recurrent NTHi infections in acute exacerbations of COPD could have important implications for clinical treatment and identification of novel bactericidal targets.

Panel 5: Immunology

Objective

To perform a state-of-the-art review of the literature from January 2012 through May 2015 on studies that advanced our knowledge of the innate and adaptive immunology related to otitis media. This review also proposes future directions for research in this area.

Data Sources

PubMed database of the National Library of Medicine.

Review Methods

Three subpanels comprising experts in the field focused on sections relevant to cytokines, innate immunity, and adaptive immunity. The review focused on animal, cell line, and human studies and was critical in relation to the recommendations from the previous publication and for determination of the proposed goals and priorities. The panel met at the 18th International Symposium on Recent Advances in Otitis Media in June 2015 to consolidate its prior search results and discuss, plan, and refine the review. The panel approved the final draft.

Conclusion

From 2012 to 2014, tremendous progresses in immunology of otitis media were established—especially in the areas of innate immunity associated with the pathogenesis of otitis media.

Implications for Practice

The advances of the past 4 years formed the basis for a series of short- and long-term research goals in an effort to guide the field. Accomplishing these goals will provide opportunities for the development of novel interventions, including new ways to better treat and prevent otitis media, especially for recurrent otitis media.

Panel 4: Report of the Microbiology Panel

Objective To perform a comprehensive review of the literature from July 2011 until June 2015 on the virology and bacteriology of otitis media in children. Data Sources PubMed database of the National Library of Medicine. Review Methods Two subpanels comprising experts in the virology and bacteriology of otitis media were created. Each panel reviewed the relevant literature in the fields of virology and bacteriology and generated draft reviews. These initial reviews were distributed to all panel members prior to meeting together at the Post-symposium Research Conference of the 18th International Symposium on Recent Advances in Otitis Media, National Harbor, Maryland, in June 2015. A final draft was created, circulated, and approved by all panel members. Conclusions Excellent progress has been made in the past 4 years in advancing our understanding of the microbiology of otitis media. Numerous advances were made in basic laboratory studies, in animal models of otitis media, in better understanding the epidemiology of disease, and in clinical practice. Implications for Practice (1) Many viruses cause acute otitis media without bacterial coinfection, and such cases do not require antibiotic treatment. (2) When respiratory syncytial virus, metapneumovirus, and influenza virus peak in the community, practitioners can expect to see an increase in clinical otitis media cases. (3) Biomarkers that predict which children with upper respiratory tract infections will develop otitis media may be available in the future. (4) Compounds that target newly identified bacterial virulence determinants may be available as future treatment options for children with otitis media.

The outcome of H. influenzae and S. pneumoniae inter-species interactions depends on pH, nutrient availability and growth phase

Haemophilus influenzae and Streptococcus pneumoniae exist together as common commensals of the healthy human nasopharynx, but both are important aetiological agents of different diseases, including the paediatric disease otitis media. It was recently shown that the formation of a multispecies biofilm of H. influenzae and S. pneumoniae is the cause of chronic forms of otitis media. However, the interactions between the two species are not clearly defined. Using a defined and kinetic analysis, our study has shown that while co-existence of the two species occurs, S. pneumoniae is also able to convert H. influenzae to a non-culturable state. We determined that this process was dependent on growth phase and pH. To analyse the H. influenzae/S. pneumoniae interactions in more depth, we investigated the growth and transcriptional profile in a pH-defined batch culture model, as well as in a growth phase independent flow cell system. Transcriptomics has shown that there are changes in gene expression in each of the species when grown in co-culture, intriguingly inducing the S. pneumoniae bacteriocin transport genes, and phage-associated genes in both species. Importantly, we have shown vast changes in gene expression in a group of S. pneumoniae metabolic genes, including those encoding lactose utilisation, glycerol utilisation and sugar transport proteins; we have shown that the expression of these genes depends not only on the presence of H. influenzae, but also on the growth system utilised.