Lower Airway Bacterial Colonization Patterns and Species-Specific Interactions in Chronic Obstructive Pulmonary Disease

Little is known about interactions between nontypeable Haemophilus influenzae, Moraxella catarrhalis, Streptococcus pneumoniae, and Pseudomonas aeruginosa in the lower respiratory tract in chronic obstructive pulmonary disease (COPD) patients. We characterized colonization by these four bacterial species, determined species-specific interactions, and estimated the effects of host factors on bacterial colonization among COPD patients. We conducted a prospective cohort study in veterans with COPD that involved monthly clinical assessment and sputum cultures with an average duration of follow-up of 4.5 years. Cultures were used for bacterial identification. We analyzed bacterial interactions using generalized linear mixed models after controlling for clinical and demographic variables. The outcomes of interest were the relationships between bacteria based on clinical status (stable or exacerbation). One hundred eighty-one participants completed a total of 8,843 clinic visits, 30.8% of which had at least one of the four bacteria isolated. H. influenzae was the most common bacterium isolated (14.4%), followed by P. aeruginosa (8.1%). In adjusted models, S. pneumoniae colonization was positively associated with H. influenzae colonization (odds ratio [OR], 2.79; 95% confidence interval [CI], 2.03 to 3.73). We identified negative associations between P. aeruginosa and H. influenzae (OR, 0.15; 95% CI, 0.10 to 0.22) and P. aeruginosa and M. catarrhalis (OR, 0.51; 95% CI, 0.35 to 0.75). Associations were similar during stable and exacerbation visits. Recent antimicrobial therapy was associated with a lower prevalence of S. pneumoniae, H. influenzae, and M. catarrhalis, but not P. aeruginosa. Our findings support the presence of specific interspecies interactions between common bacteria in the lower respiratory tracts of COPD patients. Further work is necessary to elucidate the mechanisms of these complex interactions that shift bacterial species.