Biofilms
Biofilms are organized microbial system made up of layers of microbial cells associated with surfaces and encased in adhesive polysaccharides secreted by the cells. Biofilm developing microbes possess genes that encode proteins which synthesize cell-to-cell signaling and that begin polysaccharide formation. In Pseudomonas aeruginosa, which is a notorious biofilm former, the major signaling chemicals are called homoserine lactones. The signals act as chemotactic agent to recruit nearby P. aeruginosa cells. This mechanism of biofilm making is called quorum sensing. Following are some implications of biofilms.

(i) Dental plaque represents a typical biofilm possessing acid-producing bacteria that result in dental caries (tooth decay)
(ii) Biofilms protect bacteria contained within it from being attacked by body’s immune system, antibiotics and other antimicrobial agents as these fail to pierce the biofilm.