Biofilms Presentation PDF

Biofilm and quorum sensing  Ecologists observed as early as the 1940s that more microbes in aquatic environments were found in biofilms on surfaces than were free- floating. Biofilms are complex, slime-encased communities of microbes. They are ubiquitous in nature, where they are often...

Biofilm and quorum sensing  Ecologists observed as early as the 1940s that more microbes in aquatic environments were found in biofilms on surfaces than were free- floating. Biofilms are complex, slime-encased communities of microbes. They are ubiquitous in nature, where they are often seen as layers of slime on rocks or other objects in water or at water-air interfaces.  Biofilms effects When they form on the hulls of boats and ships they cause corrosion. Of major concern is the formation of biofilms on medical devices such as hip and knee implants and indwelling catheters. These biofilms often cause serious illness and failure of the medical device. Biofilms can also form on wound scabs and delay wound healing.  Biofilm formation Biofilms can form on virtually any surface, once it has been conditioned by proteins and other molecules present in the environment. 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. The polymers are collectively called extracellular polymeric substances (EPS) or extracellular matrix (ECM), and they include polysaccharides, proteins, glycoproteins, glycolipids, and DNA. The EPS allows the microbes to stick more stably to the surface. As the biofilm thickens and matures, the microbes reproduce and secrete additional polymers.  Biofilm characteristics 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. Biofilm microbes interact in a variety of ways. For instance, the waste products of one microbe may be the energy source for another. The cells also use molecules to communicate with each other. Finally, 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.  Biofilm protects microbes 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 (figure 7.23), but it also is due to physiological changes. Indeed, numerous proteins found in biofilm cells are not observed when these cells are free-living, planktonic cells, and vice versa. When biofilms form on a medical device such as a hip implant, treatment with antibiotics often fails, which can lead to serious systemic infections.  Cell-cell communication in a biofilm Microbial cells use molecular signals to communicate with each other in a density-dependent manner. This is now referred to as quorum sensing.  Quorum sensing The first example of quorum sensing was observed in the Gram- positive, pathogenic bacterium Streptococcus pneumoniae. S. pneumoniae cells produce and release a small protein (i.e., a peptide) into the environment. As population size increases, the amount of peptide increases. Eventually the concentration of the peptide is high enough to convert some cells in the population to a competent state, that is, able to take up DNA, a process called transformation. In addition, the competent cells release a chemical called bacteriocin that lyses cells in the population that did not become competent.  Quorum sensing When noncompetent cells lyse, their DNA can be taken up by competent cells. In addition, lysed cells release virulence factors that help the competent cells invade tissues in a host organism, causing serious diseases such as pneumonia and meningitis. The marine luminescent bacterium Vibrio fischeri lives within the light organ of certain fish and squid. V. fischeri regulates its luminescence by producing a small, diffusible molecule called autoinducer. The autoinducer molecule is an N- acylhomoserine lactone (AHL). It is now known that many Gram-negative bacteria make AHL molecular signals those are derivatives of AHL. Different signal molecules Quorum sensing Quorum sensing Inter-species quorum sensing