Though biofilms were first described by Antonie van Leeuwenhoek, the theory describing the biofilm process was not developed until 1978. We now understand that biofilms are universal, occurring in aquatic and industrial water systems as well as a large number of environments and medical devices relevant for public health. Using tools such as the scanning electron microscope and, more recently, the confocal laser scanning microscope, biofilm researchers now understand that biofilms are not unstructured, homogeneous deposits of cells and accumulated slime, but complex communities of surface-associated cells enclosed in a polymer matrix containing open water channels. Further studies have shown that the biofilm phenotype can be described in terms of the genes expressed by biofilm-associated cells. Microorganisms growing in a biofilm are highly resistant to antimicrobial agents by one or more mechanisms. Biofilm-associated microorganisms have been shown to be associated with several human diseases, such as native valve endocarditis and cystic fibrosis, and to colonize a wide variety of medical devices. Though epidemiologic evidence points to biofilms as a source of several infectious diseases, the exact mechanisms by which biofilm-associated microorganisms elicit disease are poorly understood. Detachment of cells or cell aggregates, production of endotoxin, increased resistance to the host immune system, and provision of a niche for the generation of resistant organisms are all biofilm processes which could initiate the disease process. Effective strategies to prevent or control biofilms on medical devices must take into consideration the unique and tenacious nature of biofilms. Current intervention strategies are designed to prevent initial device colonization, minimize microbial cell attachment to the device, penetrate the biofilm matrix and kill the associated cells, or remove the device from the patient. In the future, treatments may be based on inhibition of genes involved in cell attachment and biofilm formation.

Biofilms: Survival Mechanisms of Clinically Relevant Microorganisms

Saliva is thought to have a significant impact on the colonization of microorganisms in the oral cavity. Salivary components may participate in this process by one of four general mechanisms: binding to microorganisms to facilitate their clearance from the oral cavity, serving as receptors in oral pellicles for microbial adhesion to host surfaces, inhibiting microbial growth or mediating microbial killing, and serving as microbial nutritional substrates. This article reviews information pertinent to the molecular interaction of salivary components with bacteria (primarily the oral streptococci and Actinomyces) and explores the implications of these interactions for oral bacterial colonization and dental plaque formation. Knowledge of the molecular mechanisms controlling bacterial colonization of the oral cavity may suggest methods to prevent not only dental plaque formation but also serious medical infections that may follow microbial colonization of the oral cavity.

Saliva-Bacterium Interactions in Oral Microbial Ecology

Resistance responses of microorganisms in food environments.

Virtually any organism can cause implant infections, but Gram-positive bacteria usually predominate. Infections due to Gram-negative bacteria and fungi, however, tend to be more serious, often requiring prompt removal of the implant. Several factors influence the microbiology of infections in implanted devices, including organisms resident at the site of implantation, itinerant pathogens that reach the implant by various mechanical means, selection of resistant organisms by antibiotics, microbial pathogenicity and ecology, and culture methods.

Pathobiology of Infection in Prosthetic Devices

Protein deposition on contact lenses: the past, the present, and the future.

Pseudomonas aeruginosa isolated from a corneal ulcer was examined for its ability to adhere to hydrophilic contact lenses with adsorbed organic films. Generally, adherence was enhanced by mucin, lactoferrin, lysozyme, immunoglobulin A, bovine serum albumin, and a mixture of these macromolecules. The water content of the lenses also influenced bacterial adherence and protein adsorption. Adherence to lenses coated with human tear films was more complex; both enhanced and inhibited adherence were observed on lenses obtained from different individuals.

L A Wilson

Papers

Effects of protein, mucin, and human tears on adherence of Pseudomonas aeruginosa to hydrophilic contact lenses.