Bacterial colonization of distal airways in healthy subjects and chronic lung disease: a bronchoscopic study

Abstract

In contrast to the healthy population, distal airway bacterial colonization may occur in patients with chronic lung diseases, who often have altered pulmonary defences. However, the information dealing with this issue is insufficient and is based mainly on nonspecific samples, such as sputum cultures.Using quantitative cultures of bronchoscopic protected specimen brush (PSB) and bronchoalveolar lavage (BAL) samples, we studied the bacterial colonization of distal airways in 16 healthy subjects, 33 patients with bronchogenic carcinoma, 18 with chronic obstructive pulmonary disease (COPD), 17 with bronchiectasis, and 32 with a long-term tracheostomy due to laryngeal carcinoma. All patients were without exacerbation, and free from antibiotic treatment at least 1 month before the study protocol. Thresholds for quantitative cultures to define colonization were ≥10 2 colony-forming units (cfu)·mL -1 for PSB and ≥10 3 cfu·mL -1 for BAL.Only one healthy subject was colonized by a potential pathogenic microorganism (PPM) (Staphylococcus aureus 4×10 2 cfu·mL -1 in a PSB culture). Colonization was observed in 14 (42%) bronchogenic carcinoma patients (19 non-PPMs, and 10 PPMs); in 15 (83%) COPD patients (22 non-PPMs and 7 PPMs); in 15 (88%) bronchiectasis patients (20 non-PPMs and 13 PPMs); and in 15 (47%) long-term tracheostomy patients (5 non-PPMs and 13 PPMs). The two most frequent nonPPMs isolated in all groups studied were Streptococcus viridans and Neisseria spp. Haemophilus spp., Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis were the most frequent PPMs isolated in bronchogenic carcinoma, COPD, bronchiectasis and long-term tracheostomized patients, respectively. Pseudomonas aeruginosa colonization was infrequent in all the groups.Our results show that distal airway bacterial colonization is a frequent feature in stable patients with chronic lung diseases and also in patients with long-term tracheostomy. However, the pattern of colonization differs among groups studied. The knowledge of different colonization patterns may be important for future antibiotic prophylactic strategies and for the empirical antibiotic regimens when exacerbations occur in these patients.

Predisposing factors to bacterial colonization in chronic obstructive pulmonary disease

“…PSB cultures resulted in $10 3 CFU . mL -1 in 55.5% (10/18) of the patients reported by CABELLO et al [10] and in 33.3% (6/18) of those reported by VEREEN et al [11]. MONSO Â et al [12], using a similar protocol to that of the present study, obtained positive PSB cultures mainly for H. influenzae and S. pneumoniae, in 10 of 40 (25%) stable COPD outpatients.…”

“…Although PSB sampling is a common and standard procedure, it may be argued that a single negative PSB sample is considered representative of the bacterial environment of the whole two lungs, assuming that PSB samples taken at the same time from other parts of the lungs would also be sterile. This has been accepted by other authors [10,12] and no previous studies addressing the reproducibility of results of PSB sampling between specimens and in different parts of the lung have been published. A standard criterion for colonization of the lower airways has not yet been defined and, although a cut-off point of $10 2 CFU .…”

“…When the subgroup of patients with PPM was considered, PSB sampling was positive in 30.7% of cases, with the degree of airflow obstruction being the only variable predictive of positive microbiological results. CABELLO et al [10] using a cut-off point of $10 2 CFU . mL -1 , recently reported bacterial colonization in 83% of clinically stable COPD patients and in 47% of long-term tracheostomized patients.…”

“…A standard criterion for colonization of the lower airways has not yet been defined and, although a cut-off point of $10 2 CFU . mL -1 was used in a recent report [10], the $10 3 CFU . mL -1 criterion was adopted here as the cut-off point as commonly used in other studies [11,12,21].…”

“…those recognized as causative pathogens of respiratory tract infections (Haemophilus influenzae, Streptococcus pneumoniae, Moraxella catarrhalis, and others) and excluding non-PPM (Streptococcus viridans, Neisseria spp. and others) [10] was carried out. Samples from expectorated sputum were not cultured.…”