The role of colonization with multi-drug resistant pathogens in an adult intensive care unit

The significance of colonization of patients with multi-drug resistant (MDR) bacteria in the pathogenesis of severe infections in the intensive care unit (ICU) environment has not been fully clarified. The roles played by the normal microbial flora as an adaptive and protective mechanism, that competing against highly virulent pathogens, and as a potential target for intervention efforts in the implementation of infection control practices, need to be underlined, in order to avoid overconsumption of antibiotics. Bacterial colonization is considered to be the first step in the pathogenesis of nosocomial infections, in synergy with the severity of underlying disease and the weakened defense mechanisms, a situation that is common in critically ill ICU patients. Colonization reflects the dynamic development of resistance of normal flora under the influence of the hospital environment and the specific risk factors associated with antibiotic administration, therapeutic interventions and the specific hospital practices in the implementation of surveillance measures and infection control. Information on a patient's colonization status can be an important part of the selection of appropriate, effective and targeted empirical antibiotic treatment of nosocomial infections. The pathogenetic pathways of colonization and development of ICU infections, and in particular of hospital pneumonia associated with mechanical ventilation (VAP), include the bronchial tree, the oropharynx and, to some extent, the digestive system. This review investigates the role of, and the risk factors for, MDR colonization in the pathogenesis of infections in the ICU setting. A preliminary report on the incidence of problematic resistant pathogens is also quoted. The significance of colonization revealed in this review comprises the following parameters: (a) The utility of selection of antibiotic treatment according to the results of surveillance cultures, as a preventive infection control measure, and (b) description of the role of colonization of the bronchial tree, pharynx and stomach in the pathogenesis of ICU infections, and in particular in the case of VAP.