Biofilm in Endoscopy

Biofilm Formation

A biofilm is a microbially derived sessile community characterized by cells that are irreversibly attached to a substratum or interface or to each other. They are embedded in a matrix of extracellular polymeric substances which they have produced. Finally, they exhibit an altered phenotype with respect to growth rate and gene transcription.

Biofilm has been described in many systems since Van Leeuwenhoek examined the plaque on his own teeth in the seventeenth century and found "animalcules".  Leeuwenhoek's skill at grinding lenses, together with his naturally acute eyesight and great care in adjusting the lighting where he worked, enabled him to build microscopes that magnified objects over 200 times, with clearer and brighter images than any of his colleagues could achieve. Looking at the samples from his mouth with his microscope, Leeuwenhoek reported: "I then most always saw, with great wonder, that in the said matter there were many very little living animalcules, very prettily a-moving". In 1683, his were among the first observations on living bacteria ever recorded.

For many years, microbiologists studied microbial cells only in their planktonic state. These observations were usually made on agar plates, where colonies of bacteria were grown and tested for antibiotic sensitivity. Aggregations of these microbes were observed long before there was a method to study them. In the late 1980’s, the confocal scanning laser microscope allowed these aggregations, known as biofilm, to be evaluated in a natural hydrated three dimensional state.

Direct microscopic observations demonstrate unequivocally that more than 99.9% of bacteria grow as aggregated sessile communities (biofilm) attached to surfaces, rather than as free floating cells in liquid. Biofilm bacteria living in highly protected and cooperative communities are genetically different and profoundly resistant to therapeutic doses of antibiotics. Bacteria form biofilm preferentially in very high shear environments where fluid moves rapidly over a surface.  Planktonic bacteria can adhere to surfaces and initiate biofilm formation in the presence of shear forces of nature that dwarfs those of heart valves.

Once a biofilm has formed and the exopolysaccharide matrix has been secreted by the sessile cells, the resultant structure is highly viscoelastic and behaves in a rubbery manner. When biofilm is formed in high shear environments it is remarkably strong and resistant to mechanical breakage. When biofilm is formed in low-shear environments, such as an endoscope, it has a lower tensile strength and breaks off easily.

The environments suitable for microorganisms to colonize and establish biofilm are practically limitless. The nature of biofilm structure and the physiological attributes of biofilm organisms confer an inherent resistance to antimicrobial agents, whether these antimicrobial agents are antibiotics, disinfectants or germicides. Microbes within biofilm can be resistant to disinfectants by multiple mechanisms, including physical characteristics of older biofilm, genotypic variation of the bacteria, microbial production of neutralizing enzymes and physiologic gradients within the biofilm (e.g. pH). Bacteria within biofilm are up to 1,000 times more resistant to antimicrobials than are the same bacteria in suspension.

Pseudomonas aeruginosa, a bacterium frequently implicated in health-care acquired infections, is a common ‘pioneer’ bacterium and is used in a lot of biofilm research. In one experiment, researchers found that Pseudomonas cells adhere to stainless steel, even to electropolished surfaces, within 30 seconds of exposure. The instant the bacteria attach to a surface, they switch on certain genes involved in the synthesis of alginate (an unusually sticky form of slime), and switching them off again once the bacteria are engulfed in alginate.

Most bacteria are studied in the planktonic state on agar plates.

Biofilm are resistant to disinfectants by multiple mechanisms including physical characteristics, genotype variations, neutralizing enzymes or gradients within the biofilm such as pH.

Next Page: Biofilm in the Human Body

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