Virulence factors in the colonization and persistence of bacteria in the airways

Haemophilus influenzae, Streptococcus pneumoniae, Moraxella catarrhalis, Staphylococcus aureus, Klebsiella pneumoniae, and Pseudomonas aeruginosa are commonly isolated from sputum specimens of patients with lower respiratory tract infections. Haemophilus influenzae, S. pneumoniae, and M. catarrhalis have several pathogenic properties in common. These bacteria are able to interact with mucus, to exert ciliotoxic activity, to adhere to bronchial epithelial cells, and to invade airway epithelium. Haemophilus influenzae and S. pneumoniae strains persist for many months in the respiratory tract of patients with chronic obstructive pulmonary disease (COPD), despite the specific antibodies present in serum and sputum against the persistent strain. Especially during exacerbations persistent strains with changes in their antigenic composition are isolated. Among H. influenzae strains, the antigenic characteristics of the outer membrane protein composition vary. Variation in S. pneumoniae occurs in capsular polysaccharides, the major immunogens of this bacterium. Such variations affect the efficacy of the antibody-mediated defense mechanisms against the bacteria. Between exacerbations, particularly H. influenzae, S. pneumoniae strains are recovered from the sputum of patients with COPD. Recovery may continue for periods up to 2 yr, although not continuously. Besides ineffective antibody-mediated defense mechanisms, it is likely that hiding of the bacteria in tissue contributes to the persistence of these bacteria in patients with COPD.