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

potential role of these strains in COPD exacerbations. Huang et al, hypothesized the presence of two bacterial microbiota related to exacerbated COPD, one characterized by a prevalence of Proteobacteria, the other by a prevalence of Firmicutes, which might be associated with more diversity. 28 The patients in the group with prevalence of Firmicutes were those with a shorter intubation period before performing the endotracheal aspirate. Moreover, a decreased bacterial diversity was correlated with the length of intubation. 28 It can be speculated that antibiotic treatment could have reduced the bacterial diversity. The limits of this study were the absence of control samples from non-intubated COPD and non-COPD patients and the lack of a longitudinal dimension. Bacteria in the oral cavity and gastrointestinal tract seed the airways in vulnerable patient populations. 24 Millares et al 29 analyzed paired sputum specimens from patients with COPD at baseline and during exacerbations, and found that exacerbations were associated with a selective increase in the relative abundance of bacteria typically associated with exacerbations (eg, Haemophilus, Pseudomonas, and Moraxella) despite inconsistent detection in culture. Huang et al 30 observed the temporal changes in the airway microbiome before, at onset, and after an acute exacerbation. They studied bacterial infections in COPD sputum samples from 12 subjects enrolled in a longitudinal study: the microbiota members that resulted increased during exacerbations, were mainly of the Proteobacteria phylum. Treatment with antibiotics alone decreased the Proteobacteria, whereas treatment with corticosteroids alone enriched the Proteobacteria and other phyla. Neither of these two studies 29,30 reported a decrease in bacterial community diversity, as would be expected after an acute infection or in more severe disease. For a better understanding of the role of the microbiome in exacerbations of COPD, there is a need for longitudinal studies in exacerbated conditions after a sufficiently extended stabilization period, including appropriate washout from pharmacological treatments, as well as in nontreated controls. The parallel analysis of the immunological host response associated with these different clinical states in COPD patients also needs to be longitudinally conducted.