The Etiology and Persistence of Cryptic Bacterial Infections: a Hypothesis

The growth and survival mechanisms used by Pseudomonas aeruginosa in human infections are similar to those used by the organism in aquatic systems. P. aeruginosa attaches to inert solid or tissue surfaces and grows predominantly in biofilms that release mobile swarmer cells into the surrounding fluid phase. These natural and pathogenic biofilms are covered by an exopolysaccharide matrix (glycocalyx) that serves as a barrier against hostile environmental factors, such as host defense mechanisms and antibiotics. Glycocalyx-enclosed biofilms of P. aeruginosa or other bacteria have been identified in experimental or clinical infections arising from contaminated prostheses and in chronic refractory infections, such as endocarditis, osteomyelitis, and P. aeruginosa pneumonia associated with cystic fibrosis. Conventional in vitro antibiotic susceptibility tests are directed against unprotected, mobile, swarmer cells. Antibiotics used to treat sequestered infections should be tested against populations of pathogens in intact biofilms to determine the ability of the antibiotics to penetrate the glycocalyces and to kill the component bacteria.