Several culture-independent studies on BAL samples illustrate that lungs are not sterile and reveal the existence of a core pulmonary bacterial microbiome in healthy lungs. Microbes present in the lung were first considered to come from the upper respiratory tract. Microbial community overlaps were observed between BAL samples and samples from the upper airway. The ebb and flow of air in and out of the lungs likely results in a compositional continuum rather than a clearly demarcated line of separation between upper and lower respiratory tract. Nevertheless, the core microbiota in healthy human lungs has been found to be comprised of a diverse assemblage of bacterial genera including species of Streptococcus, Pseudomonas, Prevotella, Fusobacterium, Haemophilus, Veillonella and Porphyromonas. Debate continues on whether the organisms present in the lower respiratory tract truly represent a resident microbiome or are transient contaminations from air and the upper respiratory tract, however, the presence of microbes in the lower lung in the disease state is far less controversial (reviewed in Nagalingam et al.).
The Pulmonary Microbiome, Mechanical Ventilation, and Trauma: Ashley D Smith, Yan Zhang, Shantanu J Shewale, Robert C Barber, Michael S Allen and Ryan M Huebinger
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Last date updated on July, 2014