The Colonization Resistance of the Digestive Tract with Special Emphasis on the Oropharynx

Abstract

In association with medical advances that have prolonged survival in both critically and chronically ill patients, including the introduction of a number of effective antimicrobial agents, a change in the pattern of many infections has occurred from acquisition outside of the hospital to acquisition within the hospital [1]. Bacterial infections of the respiratory tract have been reported to occur in 0.5 to 5.0% of hospitalized patients [2]. In a study of nosocomial infections in six community hospitals Eickhoff and associates [3] observed an adjusted rate of 3.5% for all types of nosocomial infections. Of these infections, 15.4% involved the respiratory tract and 53% of the pneumonias were associated with aerobic Gram-negative bacilli [3]. Bacteria may invade the alveolar level of the lung in sufficient numbers to produce infection by three routes: (1) haematogenously from a distant focus causing bacteremia such as Escherichia coli pneumonia during pyelonephritis [4]; (2) by suspension in inhaled gas which is a well recognized potential danger in the case of respiratory therapy, and (3) by aspiration from the pharynx, the most frequent route of lung infection. Indirect evidence supports this assumption [5, 6, 7], and the aspiration into the lung of radiopaque material instilled into the oropharynx of normal sleeping adults has been demonstrated [8]. Perhaps the most compelling evidence for the pharynx as a major source of infection of the bronchial tree is that from Johanson and coworkers, who studied the relationship of oropharynx colonization with Gram-negative bacilli to nosocomial pneumonia in patients admitted to a medical intensive care unit [9].