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SEM Micrograph of a Biofilm formed by Bacterial Colony on Silicon Substrate

Biofilm is a generic term used to describe a sludge like material that develops in association with organic materials. Biofilms result from a variety of sources, and negatively impact a number of industrial and medical applications. a Biofilm is composed of a densely packed group of microorganisms. A key property of biofilms is that individual microorganisms are bound together by a polymeric substance excreted by the microorganisms. This polymeric substance forms an adhesive matrix that holds the biofilm together, allows it to attach to surfaces, and can serve as an encapsulation which protects the colony forming the biofilm. This protective encapsulation is believed to play a role in some antibiotic-resistant infections.

The polymeric substance excreted by the microorganisms is known as an extracellular polymeric substance (EPS). It is also commonly called an extracellular adhesive matrix.

A key aspect of biofilms is a complex interaction among the constituent mircoorganisms. A biofilm forms when individual microorganisms cease to exhibit individual, free floating behavior, and begin to associate with each other, and a surface, and begin to act in concert with each other. A biofilm grows by both simple cell division, and by new free floating microorganisms associating with the developing biofilm.

Biofilms usually develop on solid surfaces immersed in a liquid.

Biofilm formation causes problems in a variety of industrial and medical applications. In macro applications, biofilms can lead to a phenomenon called biofouling, in which a biofilm grows to the point that it interferes with the intended operation of a device. An example of biofouling can be found in the shipping industry. Micro organisms like bacteria or algae can form a microfilm on the hull of a ship. This biofilm can serve as an attractive substrate for the attachment of macro organisms like seaweed or barnacles. This macro coating fouls the hull, and can impact efficiency of the vessel.

Biofouling is a common problem in water treatment plants and filtration applications where biofilms can cause clogging in filters and pipes.

Leucocyte Biofilm

SEM of Biofilm Which Encapsulated Biomedical Prototype

Biofilms can be a particular problem in the development of implantable medical devices. The image above shows a dense biofilm that had encapsulated a medical prototype. Individual white blood cells can be on the surface of the biofilm.

There are a number of mechanisms which can lead to biofilm formation on implanted devices. A simple example is that leucocytes can "find" the implant, interpret the surface as a foreign material, and trigger the formation of a dense fibrin mat around the implant. This encapsulation can yield the device non-functional. Development of successful implants requires careful selection of materials, and in particular surface properties, such that the device will not be encapsulated by the body.

Surfaces in medical implants can also be an attractive place for bacteria to attach and form a biofilm, and cause an infection.

More complex biofilms can also form involving complex interactions between bacteria, leucocytes attaching to fight the bacteria, and then a complex biofilm developing both by the body, and the bacteria.

Complex Biofilm

Complex Biofilm

The photograph above shows the initial formation of a complex biofilm. A colony of bacteria is starting to form in several areas on the surface of the device. The bacteria are the very small spherical structures. In some areas, the bacteria are clustering together, and an emerging adhesive matrix is developing around the groups of bacteria. Making this a very interesting picture is the fact that a number of much larger Leucocytes (White Blood Cells) have detected the bacterial infection, and have also attached to the surface, and appear to be forming their own biofilm in response to the bacteria.


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