Bacterial capsule

The outer red layer in this diagram is the capsule, which is distinct from the cell envelope. This bacterium is gram-positive, as its cell envelope comprises a single cell membrane (orange) and a thick peptidoglycan-containing cell wall (purple).

The bacterial capsule is a large structure common to many bacteria.[1] It is a polysaccharide layer that lies outside the cell envelope, and is thus deemed part of the outer envelope of a bacterial cell. It is a well-organized layer, not easily washed off, and it can be the cause of various diseases.[2][3]

The capsule—which can be found in both gram negative and gram-positive bacteria—is different from the second lipid membrane – bacterial outer membrane, which contains lipopolysaccharides and lipoproteins and is found only in gram-negative bacteria. When the amorphous viscid secretion (that makes up the capsule) diffuses into the surrounding medium and remains as a loose undemarcated secretion, it is known as a slime layer. Capsule and slime layer are sometimes summarized under the term glycocalyx.

A bacterial capsule has a semi-rigid border that follows the contour of the cell. The capsule excludes India Ink when dyed. A slime layer is a non-rigid matrix that is easily deformed and is not able to exclude India Ink. Biofilms are composed of many cells and their outer barriers. The primary functions of both capsules and slime layers are for protection and adhesion.
  1. ^ Peterson JW (1996). Bacterial Pathogenesis. University of Texas Medical Branch at Galveston. ISBN 9780963117212. PMID 21413346. Retrieved 17 January 2018. {{cite book}}: |website= ignored (help)
  2. ^ Gao S, Lewis GD, Ashokkumar M, Hemar Y (January 2014). "Inactivation of microorganisms by low-frequency high-power ultrasound: 1. Effect of growth phase and capsule properties of the bacteria". Ultrasonics Sonochemistry. 21 (1): 446–53. Bibcode:2014UltS...21..446G. doi:10.1016/j.ultsonch.2013.06.006. PMID 23835398. S2CID 24149924.
  3. ^ Hathaway LJ, Grandgirard D, Valente LG, Täuber MG, Leib SL (March 2016). "Streptococcus pneumoniae capsule determines disease severity in experimental pneumococcal meningitis". Open Biology. 6 (3): 150269. doi:10.1098/rsob.150269. PMC 4821241. PMID 27009189.