Biofilm, Dental Unit Water Line and Its Control

Biofilms are well-organized communities of cooperating microorganisms that can include bacteria, algae, fungi and diatoms. Dental unit waterlines (DUWL) are an integral part of dental surgery equipment, supplying water as a coolant, primarily for air turbine and ultrasonic scalers. Surveys of dental unit waterlines (DUWLs) indicate that biofilm formation is a universal problem and great majority of bacteria that have been identified from DUWL are ubiquitous, although present in only low numbers in domestic water distribution systems, but can flourish as biofilms on the lumen surfaces of narrow-bore waterlines in dental units. DUWL contamination and its significance as a factor in nosocomial infection of patients and health care workers has stressed the risk to immunocompromized persons. Not only patients but also dentists and dental personnel are at risk of being infected with opportunistic pathogens such as Pseudomonas or Legionella species by means of cross-infection or after aerosol formation from water emanating from DUWL. Several methods of decreasing the level of contamination in DUWL have been proposed. At present, the goal of this review is to discuss various aspects of biofilm formation and effective standardized disinfecting methods to maintain low bacterial counts in dental water line. This will increase the awareness of potential health risks posed by biofilm formation and provide information on techniques and devices designed to control the microbial contamination of DUWLs. Introduction Bacteria exist in two forms i.e., planktonic (free swimming) and attached forms (in communities). Traditional studies of bacterial cells in planktonic (free-swimming) phase have focussed on pure culture physiology, a model for major microbiological studies today. However, the study of planktonic bacteria does not accurately reflect the growth of bacteria in nature because different microbial life style exists when bacteria live in association with different microrganisms and with different surfaces (1). Historically, Antonie van Leeuwenhoek was the first to examine bacteria from plaque on his teeth in the 17th Century followed by the observations of thus leading to the theory of biofilms (2). A biofilm may be defined as a community of micro-organisms irreversibly attached to a surface, producing extracellular polymeric substances (EPS) (2). Bacteria in biofilm mode have an altered phenotype compared to their corresponding planktonic counterparts, particularly with regard to gene transcription, and in interaction with each other (2, 3). The conversion from a relatively simple planktonic cell to a complex, highly differentiated multi-cultural community is monitored by a close genetic regulation. In addition to bacteria, fungi, yeasts, algae, protozoa and viruses have also been isolated from biofilms in industrial and medical settings but bacteria as microganisms provide the best-studied model with regard to colonization of surfaces and subsequent biofilm formation (2). Furthermore, different biofilms are formed in different environments because of different hydrogeochemical properties. Depending upon the environment, in which biofilm formed, non living components also varies. Monocellular materials such as mineral crystals, corrosion particles, clay and silt particles, or blood components, from different environments may act as physical components of biofilms (2). Other important variables involved in cell-cell attachment and biofilm formation are: (i) properties of the substratum (texture or roughness, hydrophobicity, conditioning of film); (ii) properties of the bulk fluid (flow velocity, pH, temperature, cations, presence of antimicrobial agents); (iii) properties of the cell (cell surface hydrophobicity, fimbriae, flagella, EPS (2). BIOFILMS Biofilms are heterogeneous and complex in structure, function and metabolism. The microbes in biofilm mode exhibit coordinate behaviour and live in cooperative consortia which is identical to higher multicellular organisms (3). There are number of reasons, due to which bacteria like to live in the form of biofilms; (1) Genetic material can be easily exchanged between microrganisms;