Localization of Burkholderia cepacia Complex Bacteria in Cystic Fibrosis Lungs and Interactions with Pseudomonas aeruginosa in Hypoxic Mucus

Abstract

ABSTRACTThe localization ofBurkholderia cepaciacomplex (Bcc) bacteria in cystic fibrosis (CF) lungs, alone or during coinfection withPseudomonas aeruginosa, is poorly understood. We performed immunohistochemistry for Bcc andP. aeruginosabacteria on 21 coinfected or singly infected CF lungs obtained at transplantation or autopsy. Parallelin vitroexperiments examined the growth of two Bcc species,Burkholderia cenocepaciaandBurkholderia multivorans, in environments similar to those occupied byP. aeruginosain the CF lung. Bcc bacteria were predominantly identified in the CF lung as single cells or small clusters within phagocytes and mucus but not as “biofilm-like structures.” In contrast,P. aeruginosawas identified in biofilm-like masses, but densities appeared to be reduced during coinfection with Bcc bacteria. Based on chemical analyses of CF and non-CF respiratory secretions, a test medium was defined to study Bcc growth and interactions withP. aeruginosain an environment mimicking the CF lung. When test medium was supplemented with alternative electron acceptors under anaerobic conditions,B. cenocepaciaandB. multivoransused fermentation rather than anaerobic respiration to gain energy, consistent with the identification of fermentation products by high-performance liquid chromatography (HPLC). Both Bcc species also expressed mucinases that produced carbon sources from mucins for growth. In the presence ofP. aeruginosain vitro, both Bcc species grew anaerobically but not aerobically. We propose that Bcc bacteria (i) invade aP. aeruginosa-infected CF lung when the airway lumen is anaerobic, (ii) inhibitP. aeruginosabiofilm-like growth, and (iii) expand the host bacterial niche from mucus to also include macrophages.