Bacterial–viral load and the immune response in stable and exacerbated COPD: significance and therapeutic prospects

D’Anna, Silvestro Ennio; Balbi, Bruno; Cappello, Francesco; Carone, Mauro; Di Stefano, Antonino

Pathogenic bacteria have been identified using culture techniques in 25%-50% of patients with stable COPD. 8 A limitation of culture techniques, however, is the possibility of contamination from the upper airways. Moreover, more than 70% of bacterial species cannot be cultured by current techniques 9,10 and many of the remaining species are very difficult to culture. 11 The development of nonculture-based techniques, such as quantitative polymerase chain reaction (qPCR), has improved the capacity to detect bacteria, and has shown that the lungs are not sterile 12, 13 and that the mix of bacterial species composing the lung microbiome contributes to the disease state in chronic respiratory diseases. 14 Lower airways in COPD patients are colonized by Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis and, in patients with more severe disease, by Pseudomonas aeruginosa (Figure 1 ). [15] [16] [17] Some studies in stable-state COPD have observed a direct correlation between airway inflammation and the bacterial load, for example, before the advent of nonculture-based techniques, Hill et al 17 performed sputum cultures in 160 stable COPD patients, 55 with normal blood α 1 -antitrypsin levels, 62 with severe α 1 -antitrypsin deficiency, and 43 with idiopathic bronchiectasis, and observed that the bacterial load