44 Invasive Devices in the Pathogenesis of Nosocomial Pneumonia M. Valencia, T.T. Bauer, A. Torres 44.1 Introduction Nosocomial pneumonia remains a common complica- tion in patients who require mechanical ventilation. On various occasions endotracheal intubation has been identified as a risk factor for nosocomial pneumonia. Levine and Niederman [1] described four different de- vice/host interactions that may be responsible. First, an endotracheal tube can have direct effects on the airway, resulting in an impairment of local host defense mech- anisms. Mucosal injury can reduce mucociliary func- tion, while upper airway defenses are bypassed and the effectiveness of cough is reduced. Second, intubation can result in an enhanced capacity of tracheobronchial cells to bind Gram-negative bacteria, an effect that fa- vors airway colonization and, thus, pneumonia. Third, the airway injury can create binding sites for bacteria in the basement membrane of the bronchial tree. Fourth and most important in relation to bacterial biofilm, en- dotracheal tubes may serve as a reservoir for bacteria [1]. Recent studies have suggested that microorganisms can adhere to the surface of endotracheal tubes. Some species produce an exopolysaccharide that acts as a slime-like adhesive and the surface lining has been re- ferred to as bacterial biofilm [2]. Other invasive devices such as bronchoscopes and tracheal suction systems can also introduce microor- ganisms into the patient’s lower respiratory tract. Al- though transmission of infections by bronchoscopy de- pends on many factors, the cleaning and disinfection process is the single element that the clinician can most influence. In spite of disinfection measures several cases of nosocomial transmission of infections and pneumonia have been detected [3]. This manuscript will review the basic research relat- ed to bacterial biofilm formation on abiotic surfaces and the possible role of bacterial biofilm on the inner lumen of endotracheal tubes and the possible role of other invasive devices for the pathogenesis of ventila- tor-associated pneumonia. 44.2 Bacterial Biofilm: Definition and Formation Bacterial biofilms are defined as matrix-enclosed bac- terial populations adherent to each other and/or to sur- faces or interfaces. This definition includes microbial aggregates and also adherent populations within the pore spaces in porous media [4]. The biofilm can be regarded as a complex matrix with channels that allow nutrients to circulate analo- gous to tissues of higher organisms [5]. The sessile forms of the bacteria coated in biofilm can give rise to planktonic bacteria that may eventually leave the bio- film and disperse into the environment. Some of the bacterial species that may generate biofilms are cur- rently regarded to have only low pathogenic potential in the context of nosocomial pneumonia such as Staph- ylococcus epidermidis. However, P. aeruginosa and Streptococcus pneumoniae are common nosocomial pulmonary pathogens and their potential to aggregate in biofilms has been well described [6]. Four funda- mental steps have been identified during the process of biofilm formation and are best described for P. aerugi- nosa [6]. Flagella play an important role for the initial attachment to abiotic surfaces of P. aeruginosa during the first step of biofilm formation. Type IV pilli and twitching motility further leads to the formation of mi- crocolonies of these bacteria. Recent research has shown that strains of P. aeruginosa unable to form these initial microcolonies were also unable to form a mature biofilm on a polyvinylchloride (PVC) plastic surface [7]. Once microcolonies are formed, the at- tached bacteria have to mature into a differentiated bio- film [5]. Bacteria secrete small molecule pheromones at this stage to determine whether there are enough bac- teria to initiate the expression of a particular pheno- type (“ quorum sensing”) [8]. If this step is successful, the microcolonies differentiate into a structured, thick, biocide-resistant biofilm. Chapter 44