The lungs of patients with cystic fibrosis can contain slimy biofilms of the bacterium Pseudomonas aeruginosa, enmeshed in thick airway mucus. These biofilms present a front against antibiotics and other treatments, and patients succumb to complications from such bacterial infections, often before their mid-30s.

Credit: Reprinted with permission from Elsevier Science

Recent data have suggested that in the lung, biofilms persist under anaerobic conditions. In the October Developmental Cell, Sang Sun Yoon et al. describe experiments replicating these anaerobic biofilms in culture. They find that P. aeruginosa form denser, more robust biofilms under anaerobic (left) than aerobic conditions (right). In both images, live bacteria are stained green and dead bacteria are red. The authors went on to identify genes that assist in biofilm formation in anaerobic conditions. Among these were the outer membrane protein F (OprF) gene, which was upregulated 5-fold during aerobic biofilm growth but 39-fold during anaerobic growth. Bacteria without OprF produced very poor anaerobic biofilms. Yoon et al. provide hints that bacteria lacking OprF, a channel-forming protein, are defective in a respiratory pathway critical for anaerobic growth.

Anaerobic conditions impair the effectiveness of many 'front-line' antibiotics such as tobramycin. If anaerobic biofilm formation could be effectively inhibited, say the authors, this might give these antibiotics a second chance to work in patients with particularly resilient P. aeruginosa populations. Indeed, vaccination with OprF has been shown to protect mice against P. aeruginosa infection.