In nutrient limited ecosystems, bacteria have a marked tendency to adhere to surfaces and initiate the formation of a biofilm. A biofilm is a community of microbes, embedded in an organic polymer matrix, adhering to a surface. In nutrient limited natural and industrial ecosystems biofilm cells will predominate and cause problems as increased frictional resistance to fluids in water conduits and on ship hulls (fouling), decreased heat transfer from heat exchangers, corrosion of metallic substrata and contamination in the food and biotechnology industry. Biofilms are also a severe problem in medical science and industry causing dental plaque, contaminated endoscopes and contact lenses, prosthetic device colonization and biofilm formation on medical implants. More specifically, biofilms cause problems in a variety of areas including the bodies of humans and animals, food processing, health care facilities, metal-working shops, dairy fares and other industries.
Bacteria growing in biofilms are more resistant to antibiotics and disinfectants than planktonic cells and the resistance increases with the age of the biofilm. Bacterial biofilm also exhibits increased physical resistance towards desiccation, extreme temperatures or light. As mentioned, biofilm formation causes industrial, environmental and medical problems and the difficulties in cleaning and disinfection of bacterial biofilm with chemicals is a major concern in many industries. Furthermore, the trend towards milder disinfection and cleaning compositions may increase the insufficient cleaning of surfaces covered with biofilm.
In fact, one of the apparent purposes of natural biofilm formation is for the protection of the constituent microbes from a hostile environment. Consequently, there is a combative interaction between microbes in biofilms and biocidal vehicles such as preservatives, disinfectants and antibiotics. Further, the sessile mode of bacterial growth in biofilms differs from that of the same bacteria species that are present as planktonic cells in a circulating aqueous medium which interfaces with the biofilm. Biofilms also act as a trap for nutrient acquisition, which is an important factor when bacteria grow on surfaces and the nutrient supply is oligotrophic.
Biofilms consist of both host microbes and their extracellular products, usually exopolysaccharides. Microbes have a tendency to form these protective exopolysaccharide matrices after they have adhered to a surface. The formation of biofilm complexes requires only humid conditions and/or water systems and contact with a support surface and/or interface. With respect to nutrients, a nutrient deficiency in fact may increase the biofilm formation capacity of microbes. See 29 Adv. Appl. Microbiol. 93 (1983).
In general, biofilms can be produced by almost all microbes under suitable conditions. Various bacteria have been detected in biofilms, including several bacteria having pathogenic potential, such as Flavobacterium, Moraxella, Achromobacter, Pseudomonas, Alcaligenes, Micrococcus and Legionella. All of these bacteria have the potential to cause infections in humans, and Legionella, which is highly resistant to antibiotics, is of particular concern since infection can be fatal. The most common biofilm producers belong to the genera Pseudomonas, Enterobacter, Flavobacterium, Alcaligenes, Staphylococcus, and Bacillus. There also are anaerobes that can construct corrosive biofilms.
Bacterial deposits on the surfaces of food processing equipment can lead to potential contamination of food products. Bacterial deposits on medical devices such as implants, catheters and intraocular lenses also present the potential for infection when in contact with patients and medical personnel. Consequently, good hygiene standards require that food processing equipment be thoroughly cleaned between uses and that medical and dental equipment be sterilized if possible or at least, for non-surgical instruments, thoroughly cleaned before use. Other surfaces proximate to food processing or medical equipment, such as flooring, walls, tiles, conveyor belts, drains, and packaging, also should be regularly cleaned. Nonetheless, the potential always exists for residual bacterial deposits or for the incidental growth of bacteria on cleaned surfaces, particularly after contact with biological materials as encountered in food processing, e.g., blood, fats, and proteins. For equipment that cannot be thoroughly sterilized between uses, such as most food processing equipment, the potential exists for residual bacteria surface deposits because of the tenacious adherence of bacterial biofilms to the material of the processing equipment, commonly stainless steel but also often including other metals and polymers. Biofilms are communities of microorganisms adhering to surfaces of substrates, usually within a matrix of extracellular polymeric substances. Contamination of biological origin (hereafter biological contamination) on surfaces can include biofilms, blood, proteins, fats, oils, or combinations of such materials.
Besides causing problems in cleaning and hygiene, biofilms can cause energy losses and blockages in condenser and heat exchange tubes, interfere with water and waste water systems, and form drag-inducing encrustations on ship hulls. In the medical disciplines, a biofilm (referred to as “glycocalyx”) formed by bacteria such as a Pseudomonas species can be the systemic causation of diseases of the lungs or the gastrointestinal and urinary tracts. Additionally, a biofilm formed by bacteria such as Staphylococcus species can be a serious contamination problem in foreign-body instruments such as cardiac pacemakers, catheters, prostheses, artificial valves, and the like. Dental plaque is also a typical form of biofilm.