It has been increasingly recognized that many infections are caused by bacteria that do not grow individually (planktonically); rather, they exist in complex multicellular communities in which the microbes are sessile. Typically, microbial com munities form on surfaces, hence “biofilm.” For example, it is routine to debride our teeth every day to remove the bacterial biofilm that accumulates while we sleep. Similarly, biofilms are associated with Streptococcus viridians on heart valves, Pseudomonas aeruginosa lung infections, Staphylococcus aureus on catheters, or Legionella pneumophila colonization of hospital water systems, among many others. In nature, biofilms often consist of several different microbial species. Understanding the growth of bacterial bio films has become an increasingly important aspect of medical microbiology.

A variety of stressors trigger biofilm formation, and each microorganism is unique in the signals it responds to. Bio films begin with a single bacterium attaching on a surface followed by binary fission and ultimately to the formation of an intimate community of progeny bacteria. Eventually this bacterial community surrounds itself with a glycocalyx for environmental protection. The glycocalyx also serves to keep the biofilm community intact. Bacteria within a biofilm produce small molecules, such as homo serine lactones, which are taken up by adjacent bacteria and functionally serve as a colony “telecommunication” system, informing individual bacteria to turn on certain genes at a particular time (Quorum Sensing). These signals are known as quorum sensors.

Conceptually, the strategy of biofilm formation is logical. It promotes increased metabolic diversity. For example, bacteria on the periphery of the biofilm may have more access to oxygen and other nutrients than organisms on the inner portions of the film. On the other hand, cells on the inner portions may be shielded from predation by immune cells, or from antibiotics. Intimately attached bacteria may be able to efficiently transfer genes that would result in phenotypic versatility when compared to planktonic cells. Because of all these variables it is difficult to mathematically model biofilm growth as compared to growth in batch culture. This is an important area of medical microbiology that needs to be considered in the larger context of infectious disease.

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مواضيع ذات صلة

Strategies to Control Bacteria at the Environmental Level

Definition and Measurement of Bacterial Death

Morphologic Changes During Growth

Staining

Endospores

The Acid-Fast Cell Wall

Special Components of Gram-Negative Cell Walls

Special Components of Gram-Positive Cell Walls

The Peptidoglycan Layer

Bacterial Cultivation

Principles of Bacterial Cultivation : Environmental Requirements

Structure and Function of the Bacterial Cell