Interactions and mechanisms of respiratory tract biofilms involving Streptococcus pneumoniae and nontypeable Haemophilus influenzae

The pathology associated with human respiratory tract bacterial agents that exist as opportunistic commensals in the nasopharynx cause infections. This is particularly true for the middle ear disease otitis media (OM) and exacerbations of chronic obstructive pulmonary disease (COPD). Streptococcus pneumoniae and nontypeable Haemophilus influenzae (NTHi) are a commonly recurrent combination and the formation of bacterial biofilms by these pathogens in the bronchial airway or middle ear contributes significantly to the chronic nature of these diseases. While S. pneumoniae and NTHi have been extensively studied in mono-culture, our knowledge about how they exist together, either in their free-living (planktonic) form or as a biofilm, or indeed the implication of co-infection is still limited. Several key elements are believed to contribute or are induced: (1) a set of sugar metabolic pathways; (2) surface structures in S. pneumoniae and NTHi when they are able to co-exist equally; (3) epithelial cell contact that dramatically increases the rate of biofilm formation; (4) chemical modifications of NTHi surface structures involved in host cell interactions; and (5) transcription factors that regulate particular surface molecules and the switch to a biofilm state. There appears to be multiple mechanisms involved and that these are active under specific conditions.