Biofilms

Biofilms

Any surface exposed to the environment will, initially be coated with the surrounding environmental constituents (e.g. water, electrolytes and various organic and non-organic substances). It is likely that the presence of water, electrolytes and other substances could provide the stimulus for microbial growth and its further colonisation onto the material surfaces in vitro. Subsequently, any surface or material will likely to be affected in whatever its role or function. If the surface or material is used in a hospital or a food preparation environment, then it is essential that surface be free from any bio-contamination.

Stage 1

Bacteria posses a particular affinity for surfaces, be that electrostatic (ionic) or through dispersion forces (van der waals interactions), although the true nature is still hotly debated. Typically, free-floating bacteria (planktonic bacteria) within a medium will encounter a surface – now coated with environmental constituents – and adsorb onto the surface. At this stage, this adsorption in entirely reversible and occurs in a relatively short period of time of only seconds once exposed.

Stage 2

If the bacterium remains adsorbed on to the surface long enough, an irreversible attachment takes place as the bacterium undergoes chemical and physical changes.

Stage 3

As the numbers of bacterium cells adsorb onto a surface, they start to secrete a polysaccharide substance (EPS – extracellular substances). As the name suggests EPS are complex polymeric sugars such as glucose, galactose, fructose and others. This layer can now entrap particulate matter (e.g. clay, organic matter, dead cells and minerals) adding to the bulk and diversity of the biofilm.

Staphylococcus_aureus_biofilm_01

It was originally thought that biofilm was a simply layer with bacterium randomly scatted around. However it was discovered that in sufficient numbers, bacterium signal each other to re-organise into vast arrays of structures, with intricate channels that deliver nutrients and remove waste products. As the biofilm matures, the film protects the bacterial community from changing environmental conditions, such as pH, temperature, salinity etc, and the presence of biocides.

So, you can imagine that once biofilm takes hold on a surface, it is tough to remove effectively, although not impossible. Even chlorine (hypochlorite) used in water treatment facilities is relatively ineffective against biofilms.

The key to their survival in hostile environments is their genetic adaptability to each situation and use of genetic mutations brought about by differing nutrient composition. This gives the ability and of the bacteria to cope with varying environmental conditions by varying the precise composition of the biofilm.

Although greatly beneficial to bacterial survival, biofilm can cause significant damage to surface materials and habour deadly sources of pathogenic bacteria.

Biofilms and their role in various nosocomial infections

From a health and hygiene point of view, there is an excellent article published in Dartmouth Undergraduate Journal of Science (DUJS). Below i have cited directly the pertinent point:

“More immediately, some forms can even threaten the lives of humans. Biofilms are associated with many human diseases including periodontitis in the teeth and cystic fibrosis in the lungs, as well as various nosocomial infections acquired from hospitals. Other kinds of bacteria can also attach to implanted medical devices and persist through the formation of a biofilm. One man, for example, suffered from pacemaker endocarditis and recovered only after removal of the pacemaker. Endocarditis, the inflammation of the heart valve, occurs when the infecting organism enters the bloodstream and settles in the heart. In the United States, it targets approximately 19,000 people each year. The infectious organism is usually “streptococci (‘strep’), staphylococci (‘staph’), or species of bacteria that normally live on body surfaces”. This case is notable in that drugs alone could not cure his condition; instead, the specific source of bacteria had to be eliminated. The infected pacemaker did, in fact, turn out to have “localized accretions of coccoid bacteria,” in this case Staphylococcus aureus.

Biofilms have been found to preserve the bacteria that form them, but often exacerbate health problems for humans. Above are Staphylococcus aureus biofilms.

This strong resistance to antibiotics makes biofilms difficult to target by medical means. Antibiotics can attack the planktonic cells that are released from the biofilm. But the bacterial colony surrounded by biofilm is at least 500 times more resistant to antibiotics. Even after the planktonic bacteria dispersed throughout the body are eliminated, the biofilm, the source of the infectious disease, persists. Such a resistance is due to several factors: the failure of the antibacterial agent to fully penetrate into the biofilm, the existence of slow-growing cells in the biofilm that are not susceptible to antibiotics, and the protective phenotype of the biofilm itself. Researchers are thus attempting to target these characteristics of the biofilm”.

 

References:

http://dujs.dartmouth.edu/fall-2009/biofilms-bacteria%E2%80%99s-elixer-of-survival