Abstract
BackgroundThere has been increasing interest in the use of newer, culture-independent techniques to study the airway microbiome of COPD patients. We investigated the relationships between the three common potentially pathogenic microorganisms (PPMs) Haemophilus influenzae, Streptococcus pneumoniae and Moraxella catarrhalis, as detected by quantitative PCR (qPCR), and inflammation and health status in stable patients in the London COPD cohort.MethodsWe prospectively collected sputum, serum and plasma samples for analysis of airway bacterial presence and load, and airway and systemic inflammation from 99 stable COPD patients between January 2011 and October 2012. Health status was measured with St George’s Respiratory Questionnaire and COPD Assessment Test.ResultsAirway inflammation and plasma fibrinogen, but not C-reactive protein, were greater in samples with PPM detection (p < 0.001, p = 0.049 and p = 0.261, respectively). Increasing total bacterial load was associated with increasing airway (p < 0.01) but not systemic inflammation (p > 0.05). Samples with high total bacterial loads had significantly higher airway inflammation than both samples without PPM detection and those with lower loads. Haemophilus influenzae presence was associated with significantly higher levels of airway but not systemic inflammation for all given pathogen loads (p < 0.05), and was significantly greater than with other PPMs. No association was observed between inflammation and health status (p > 0.05).ConclusionsAirway and systemic inflammation, as measured by fibrinogen, is greater in stable COPD patients with PPMs detected using the culture-independent qPCR technique. The airway, but not systemic inflammatory response, appears to have a total pathogen-load threshold and appears attributable to Haemophilus influenzae. However, discordance between inflammation and health status was observed.Electronic supplementary materialThe online version of this article (doi:10.1186/s12931-014-0114-1) contains supplementary material, which is available to authorized users.
Highlights
There has been increasing interest in the use of newer, culture-independent techniques to study the airway microbiome of Chronic obstructive pulmonary disease (COPD) patients
There were no significant differences in baseline characteristics between the two groups
Sputum bacterial isolates and loads One or more potentially pathogenic microorganisms (PPMs) were identified by quantitative polymerase chain reaction (qPCR) in 64/183 (35%) of sputum samples and these samples were defined as lower airway bacterial colonisation (LABC)
Summary
There has been increasing interest in the use of newer, culture-independent techniques to study the airway microbiome of COPD patients. Studies using such techniques have demonstrated the presence of a wide range of bacterial species in healthy individuals, described as the core microbiome, which may become disrupted in disease states [15] These techniques are expensive and timeconsuming to perform and analyse, limiting their use to small sample numbers. The culture-independent quantitative polymerase chain reaction (qPCR) technique targeting commonly isolated PPMs in COPD; HI, SP, and MC, has been shown to be more discriminatory than culture, detecting a higher prevalence of PPMs at both stable and exacerbation states [16] This technique is relatively inexpensive and can be used to examine much larger sample numbers
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