Impact of micro-environmental changes on respiratory tract infections caused by intracellular bacteria.

Community-acquired pneumonia is caused by intra- and extracellular bacteria, some of which are also linked to the pathogenesis of chronic lung diseases, such as asthma and chronic obstructive pulmonary disease (COPD). Chlamydia pneumoniae is an obligate intracellular pathogen that is highly sensitive to micro-environmental conditions that control both pathogen growth and host immune responses. Availability of nutrients, as well as changes in oxygen, pH and interferon-γ (IFNγ) levels have been shown to directly influence chlamydial life cycle and clearance. Although the lung has been traditionally regarded as a sterile environment, sequencing approaches have enabled the identification of a large number of bacteria in healthy and in diseased lungs. The influence of the lung microbiota on respiratory infections has not been extensively studied so far, and data on chlamydial infections are currently unavailable. In this article, we speculate on how the lung microbiota might interfere with acute and chronic infections by focusing exemplarily on C. pneumoniae. Furthermore, we consider changes in the gut microbiota as an additional player in the control of lung infections, especially in view of the increasing evidence suggesting involvement of the gut microbiota in various immunological processes throughout the human body. This article is protected by copyright. All rights reserved.