Haemophilus influenzae Forms Biofilms on Airway Epithelia: Implications in Cystic Fibrosis

Biofilms are increasingly recognized as contributing to disease pathogenesis in cystic fibrosis (CF) and other respiratory tract diseases associated with chronic bacterial infections. Pseudomonas aeruginosa in CF sputum displays morphologic and physiologic evidence suggestive of biofilm formation in vivo (1, 2). Biofilms enable bacteria to persist in CF pulmonary infections (for a review, see Reference 3). P. aeruginosa in a biofilm state can exhibit a more than 1,000-fold increase in antibiotic resistance (4) and more readily evades host defense factors (5). Nontypeable Haemophilus influenzae (NTHi) has recently been shown to form biofilms in vitro and in otitis media (OM) (6-10); however, there is no information on NTHi biofilm formation in the lung or in CF.

NTHi commonly infects patients with CF, especially early in childhood (11, 12). It is hypothesized that H. influenzae causes inflammation and damage to the airway and acts as a gateway organism paving the way for colonization with P. aeruginosa (13). Supportive of this, most children with P. aeruginosa had prior infection with H. influenzae or Staphylococcus aureus ( 14), and single-pathogen infections with H. influenzae, S. aureus, or P. aeruginosa showed no statistically significant differences for airway inflammatory markers (15).

We hypothesized that NTHi forms biofilms on airway epithelia, which leads to increased airway epithelial inflammatory responses. We further hypothesized that NTHi biofilms form in the lungs of patients with CF in childhood and may contribute to early lung disease pathogenesis. Some of the results of these studies have been previously reported in the form of abstracts (16, 17).

METHODS

All bronchoalveolar lavage fluid (BALF) and bacterial culture samples used in these studies were obtained using protocols approved by the institutional review board at the University of Iowa.

Human BAL Samples