Infection's Biology: Biofilms

Biofilms are conglomerations of bacteria (or certain fungi) within a ‘slime’ of polysaccharides, proteins and DNA. This extracellular matrix assists bacteria in adhering to surfaces and can be formed by some bacterial strains when they change from a free-living ‘planktonic’ form to a sessile form for example on the surfaces of teeth, heart valves, lungs but also on implants, in skin wounds or when floating on moist surfaces such as sewage or even disinfectant footbaths. In nature, biofilms are ubiquitous and although biofilm-associated bacteria grow slower than their planktonic counterparts, biofilms help bacteria to thrive in difficult or even extreme conditions such as hot springs or on glaciers. However, over the past 20 years, biofilms have become recognized as a serious problem for public health as they facilitate many important microbial infections in humans and animals, including wound and implant-related infections, and substantially complicate their treatment.

The impact of biofilms on microbial infection stems from their ability to protect pathogens from antimicrobial drugs and disinfectants (intrinsic resistance), to help to retain nutrients and to protect microbes from host immune responses (antibodies can penetrate biofilms and phagocytes engulf them but the resulting immune reactions are reduced). In addition, the formation of phagocyte agglomerations around biofilms can lead to capsule formation and interfere with wound healing. The microenvironment within biofilms includes signaling channels that facilitate bacterial communication and possibly exchange of resistance genes (acquired resistance) and lead to a change in gene expression and production of virulence factors that are not typically expressed by planktonic forms. Detachment and expulsion of aggregates of biofilm allows the spread of infection and may facilitate thromboembolic disease.  [...]