Prevalence and Load of Airway Bacteria in Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is defined by irreversible airflow limitation, usually caused by exposure to noxious particles or gases. COPD patients suffer from chronic daily symptoms, and may occasionally suffer acute exacerbations – episodes in which there is a worsening of symptoms above day-today levels. Exacerbation aetiology is variable and controversial, although infection and air pollution are believed to play a part. Certain bacterial pathogens, known as typical airway bacteria, are found with high prevalence in individuals at exacerbation. The burden of other airway bacteria is currently ill-defined. This study initially compared microbiological culture with quantitative PCR for detection of three commonly identified airway bacteria in COPD, Haemophilus influenzae, Streptococcus pneumoniae, Moraxella catarrhalis (typical airway bacteria). Quantitative PCR was utilised to establish prevalence and load of these species at stable, exacerbation and exacerbation recovery states. Typical airway bacterial prevalence and load was assessed against a range of clinical factors in COPD. Additional quantitative PCRs examined the prevalence and load of atypical airway bacteria (Chlamydophila pneumoniae, Legionella pneumophila, Mycoplasma pneumoniae) and the entire bacterial microflora of the lungs. My original contribution to knowledge is that higher load of typical airway bacteria is associated with higher levels of systemic inflammation and airflow limitation in both stable and exacerbated COPD. For the first time it has also been demonstrated that airway microbiome load is not associated with airflow limitation or systemic inflammation changes, providing evidence that typical airway bacteria in particular are contributing to disease severity. Atypical airway bacteria prevalence in COPD was negligible. The investigations in this thesis highlight the need for rapid antibiotic therapy in exacerbations where typical airway bacteria presence is suspected or confirmed. Furthermore, prophylactic antibiotic therapy should be considered for stable COPD patients with confirmed typical airway bacterial presence, as a means of reducing inflammation and airflow limitation

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

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

Changes in prevalence and load of airway bacteria using quantitative PCR in stable and exacerbated COPD

BACKGROUND: Prevalence and load of airway bacteria in stable and exacerbated chronic obstructive pulmonary disease (COPD) has been previously studied using microbiological culture. Molecular techniques, such as quantitative PCR (qPCR), may be more informative. METHODS: In this study, 373 sputum samples from 134 COPD outpatients were assessed for prevalence and load of typical airway bacteria (Haemophilus influenzae, Streptococcus pneumoniae, Moraxella catarrhalis) by multiplex qPCR, with 176 samples analysed for atypical bacteria. Paired stable and exacerbation typical bacteria data were compared in 52 patients. We compared routine culture with qPCR in 177/373 samples. RESULTS: Typical bacteria were more prevalent in exacerbation than stable-state paired samples: 30/52 (57.7%) vs. 14/52 (26.9%); p=0.001. In patients who were bacteria-positive at both time points, mean (±1 SEM) load was significantly higher at exacerbation than stable state (108.5(±0.3) vs. 107.2(±0.5) cfu/ml), constituting a 20-fold increase (p=0.011). qPCR was more discriminatory at detecting typical bacteria than microbiological culture (prevalence 59.3% vs. 24.3%; p<0.001). At stable state, higher airway bacterial load correlated with more severe airflow limitation (FEV(1)%predicted) (r=-0.299; p=0.033) and higher inhaled corticosteroid dosage (r=0.382; p=0.008). Mean C-reactive protein was higher in bacterial-associated exacerbations (35.0 Vs 25.1 mg/L; p=0.032). CONCLUSIONS: Airway bacterial prevalence and load increase at COPD exacerbations and are an aetiological factor. qPCR is more discriminatory than culture, identifying higher airway bacterial prevalence. Exacerbations associated with bacterial detection showed a higher mean C-reactive protein level. In the stable state, airway bacterial load is related to more severe airflow limitation and higher inhaled corticosteroid dosage used