Planktonic and sessile (biofilm) growth

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Chapter: Pharmaceutical Microbiology : Fundamental features of microbiology

Bacteria growing in liquid culture in the laboratory usually exist as individual cells or small aggregates of cells suspended in the culture medium; the term planktonic is used to describe such freely suspended cells.


PLANKTONIC AND SESSILE (BIOFILM) GROWTH

 

Bacteria growing in liquid culture in the laboratory usually exist as individual cells or small aggregates of cells suspended in the culture medium; the term planktonic is used to describe such freely suspended cells. In recent years, however, it has become recognized that planktonic growth is not the normal situation for bacteria growing in their natural habitats. In fact, bacteria in their natural state far more commonly grow attached to a surface which, for many species, may be solid, e.g. soil particles, stone, metal or glass, or for pathogens, an epithelial surface in the body, e.g. lung or intestinal mucosa. Bacteria attached to a substrate in this way are described as sessile, and are said to exhibit the biofilm or microcolony mode of growth.

 

Planktonic cells are routinely used for almost all the testing procedures that have been designed to assess the activity of antimicrobial chemicals and processes, but the recognition that planktonic growth is not the natural state for many organisms prompted investigations of the relative susceptibilities of planktonic and bio-film grown cells to antibiotics, disinfectants and decontamination or sterilization procedures. In many cases it has been found that planktonic and sessile bacteria exhibit markedly different susceptibilities to these lethal agents, and this has prompted a reappraisal of the appropriateness of some of the procedures used.

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