Biofilms

Biofilms

  1. Although ecologists observed as early as the 1940s that more microbes in aquatic environments were found attached to surfaces (sessile) than were free-floating (planktonic), only relatively recently has this fact gained the attention of microbiologists. These attached microbes are members of complex, slime-encased communities called biofilms.
  2. Biofilms are ubiquitous in nature, where they are most often seen as layers of slime on rocks or other objects in water or at water-air interfaces. When they form on the hulls of boats and ships, they cause corrosion, which limits the life of the ships and results in economic losses.
  3. Major concern is the formation of biofilms on medical devices such as hip and knee implants. these biofilms often cause serious illness and failure of the medical device.
  4. Biofilms can form on virtually any surface, once it has been conditioned by proteins and other molecules present in the environment.
  5. Initially microbes attach to the conditioned surface but can readily detach. Eventually they form a slimy matrix made up of various polymers, depending on the microbes in the biofilm.
  6. The polymers are collectively called extracellular polymeric substances (EPS), and they include polysaccharides, proteins, glycoproteins, glycolipids, and DNA.
  7. The EPS matrix allows the microbes to stick more stably to the surface. As the biofilm thickens and matures, the microbes reproduce and secrete additional polymers.
  8. A mature biofilm is a complex, dynamic community of microorganisms. It exhibits considerable heterogeneity due to differences in the metabolic activity of microbes at various locations within the biofilm; some are persister cells.
  9. Biofilm microbes interact in a variety of ways. the waste products of one microbe may be the energy source for another microbe.
  10. DNA present in the EPS can be taken up by members of the biofilm community. Thus genes can be transferred from one cell (or species) to another.
  11. While in the biofilm, microbes are protected from numerous harmful agents such as UV light and antibiotics. This is due in part to the EPS in which they are embedded.
  12. The resistance of biofilm cells to antimicrobial agents has important consequences. When biofilms form on a medical device such as a hip implant, treatment with antibiotics often fails, which can lead to serious systemic infections.
  13. The treatment failure is in part due to the presence of persisters in the biofilm. The persisters survive antibiotic treatment and then repopulate the biofilm once treatment ceases. Often the only way to manage patients in this situation is by removing the implant.
  14. Another problem with biofilms is that cells are regularly sloughed off. This can have many consequences. For instance, biofilms in a city's water distribution pipes can serve as a source of contamination after the water leaves a water treatment facility.
  15. Biofilms  bacterial cells using molecular signals to communicate with each other in a density-dependent manner were discovered. This is now referred to as quorum sensing.
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