Inflammatory thresholds and the species-specific effects of colonising bacteria in stable chronic obstructive pulmonary disease

Abstract

Background: There 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.

Methods: We 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.

Results: Airway 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).

Conclusions: Airway 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.

Figure 1

Bacterial colonisation status and BronkoTest® colour. (A) Proportion of colonised (LABC) and non-LABC sputum samples according to BronkoTest® colour chart. (B) Relationship between BronkoTest® colour and total bacterial load by qPCR.

Figure 2

Relationship between total bacterial load, as measured by qPCR, in colonised samples (n = 64) and (A) CXCL8, (B) IL-1β, and (C) MPO.

Figure 3

Inflammatory thresholds of (A) CXCL8, (B) IL-1β, and (C) MPO. Low load samples were defined as a total bacterial load of ≤10^7.0 cfu.ml^-1 (n = 32) and high load as >10^7.0 cfu.ml^-1 (n = 32). LABC = lower airway bacterial colonisation.

Figure 4

The species-specific effect of potentially pathogenic microorganisms (PPMs) on (A) CXCL8, (B) IL-1β, and (C) MPO. LABC = lower airway bacterial colonisation; HI = Haemophilus influenzae; SP = Streptococcus pneumoniae; MC = Moraxella catarrhalis; mixed = mixed potentially pathogenic microorganisms.

Figure 5

Multiple regression analysis showing change in (A) CXCL8, (B) IL-1β, and (C) MPO in relation to the bacterial load of single isolate Haemophilus influenzae (HI, n = 21), Streptococcus pneumoniae (SP, n = 21) and Moraxella catarrhalis (MC, n = 7) and mixed-potentially pathogenic microorganisms (PPMs) (mixed, n = 15) samples.