Bacterial colonization of the tracheobronchial tree.

Bacterial colonization of the tracheobronchial tree is a significant problem in hospitalized and chronically ill individuals. Colonization occurs because of both microbial and host factors, with the foremost mechanism being adherence of pathogenic gram-negative bacteria to mucosal epithelial cells. In the pathogenesis of nosocomial pneumonia, colonization appears to be an essential first step. In the diagnostic approach to hospital-acquired pneumonia, a distinction must be made between colonization and true lower respiratory tract infection. Future approaches to the major problem of colonization with gram-negative bacteria will require a better understanding of pathogenesis and employ strategies that not only focus upon limiting the bacterial pathogens but also attempt to improve upon pulmonary defense mechanisms.