Biofilm is a mucous substance that bacteria secrete and in which they embed themselves. Biofilms are part of the bacterial defences against the immune system and constitute a barrier to the body’s immune cells as these encounter considerable difficulties penetrating the biofilm in order to target the bacteria inside.
Biofilms are complex structures with well organised own fluid systems. Biofilm consists of approximately 95 % water.
Longer version:
Bacterial biofilm consist of a gel-like matrix of extracellular material secreted by bacteria. They are inhabited by bacteria that form highly complex, well-organised communities. Biofilm consists of up to 95% water and usually has defined architectural structures, including its own water channel systems, and is optimised for the survival and proliferation of the bacterial communities encased within them.
Biofilm formation is a stepwise transition of bacteria from the planktonic (free swimming) form into its distinct sessile (attached) form with the two forms exhibiting very different gene expression. Within the biofilm the bacteria form aggregates, where they are physically joined together. In wounds, these aggregates or biofilms are typically attached to the wound surface and strongly increase the virulence and survival of the bacteria. Biofilm can be viewed as a defence fortification that is difficult to impossible for the immune cells and antibiotics to penetrate.
The photo is an example of a wound covered with biofilm: The wound edges and surrounding tissue demonstrate that the wound is very well cared for and it often seems inexplicable why it has stopped reducing in size. That is a typical clinical observation of a chronic ulcer containing biofilm.
An extreme tolerance of antimicrobial agents is known to be one of the major hallmarks of biofilms. (Bjarnsholt T 2013)
Between 60% and 90% of chronic wounds have biofilm formation. (Keast et al. 2014)
Efficacy of antibiotics in biofilm infections: 25-30%. (Keast et al. 2014)