Antibiotic resistance in biofilms

Abstract

Biofilms are microbial communities encased in polysaccharide-rich extracellular matrices and living in association with surfaces (1). Biofilm formation is an important process for survival of microbial pathogens in the environment (e.g., Vibrio cholerae) or in the mammalian host (e.g., Pseudomonas aeruginosa). Free-swimming (planktonic) microbial cells attach, first transiently and then permanently as a single layer, to an inert surface or to a tissue. This monolayer gives rise to larger cell clusters that eventually develop into a highly structured biofilm, consisting of mushroom-shaped bacterial microcolonies separated by fluid-filled channels. The channels allow nutrients to reach all levels of the biofilm and toxic waste products to diffuse out (2-8). Biofilms are formed particularly in high-shear environments: the respiratory and urinary tracts, the oropharynx, and native heart valves. Thus, biofilm formation is an important aspect of many chronic human infections: dental caries, middle ear infections, medical device-related infections (ocular/cochlear implants, orthopedic devices, indwelling catheters, IUDs), native/prosthetic valve endocarditis, osteomyelitis, prostatitis, and chronic lung infections in cystic fibrosis patients (9-18). For bacterial biofilm formation, cell-to-cell communication (quorum sensing) may be required (19). Signal molecules produced by bacteria accumulate locally, triggering elaboration of virulence factors and biofilms.