Gram-positive bacteria 12936 223448628 2008-07-04T03:20:39Z Zorrobot 7218328 robot Modifying: [[eo:Gram-pozitivaj bakterioj]] [[Image:Gram_Stain_Anthrax.jpg|thumb|right|300px|Gram-positive [[Bacillus anthracis]] bacteria (purple rods) in [[cerebrospinal fluid]] sample. The other cells are [[white blood cell]]s]] '''Gram-positive''' [[Bacteria|bacteria]] are those that are stained dark blue or violet by [[Gram staining]]. This is in contrast to [[Gram-negative]] bacteria, which cannot retain the crystal violet stain, instead taking up the [[counterstain]] ([[safranin]]) and appearing red or pink. Gram-positive organisms are able to retain the crystal violet stain because of the high amount of [[peptidoglycan]] in the [[cell wall]]. Gram-positive cell walls typically lack the outer membrane found in Gram-negative bacteria. ==Characteristics== [[Image:Gram-Cell-wall.svg|thumb|right|300px|Gram-positive and -negative cell wall structure]] [[Image:Gram-positive cellwall-schematic.png|thumb|right|Structure of Gram-positive cell wall]] The following characteristics are generally present in a Gram-positive bacterium:<ref name=Brock>{{cite book | author = Madigan M; Martinko J (editors). | title = Brock Biology of Microorganisms | edition = 11th ed. | publisher = Prentice Hall | year = 2005 | id = ISBN 0131443291 }}</ref> #Cytoplasmic lipid membrane #Thick [[peptidoglycan]] layer #*[[Teichoic acids]] and [[lipoteichoic acid]]s are present, which serve to act as [[Chelation|chelating]] agents, and also for certain types of adherence. #Capsule [[polysaccharides]] (only in some species) #[[Flagellum]] (only in some species) #*If present, it contains two rings for support as opposed to four in Gram-negative bacteria because Gram-positive bacteria have only one membrane layer. ==Classification== In the original bacterial phyla, the Gram-positive organisms made up the [[phylum (biology)|phylum]] [[Firmicutes]], a name now used for the largest group. It includes many well-known genera such as ''[[Bacillus]]'', ''[[Listeria]]'', ''[[Staphylococcus]]'', ''[[Streptococcus]]'', ''[[Enterococcus]]'', and ''[[Clostridium]]''. It has also been expanded to include the Mollicutes, bacteria like ''[[Mycoplasma]]'' that lack cell walls and cannot be Gram stained, but are derived from such forms. [[Actinobacteria]] are the other major group of Gram-positive bacteria, which have a high [[guanosine]] and [[cytosine]] content in their genomes (high G+C group). This contrasts with the Firmicutes, which have a low G+C content. Both Gram-positive and Gram-negative bacteria may have a membrane called an [[S-layer]]. In Gram-negative bacteria, the S-layer is directly attached to the [[outer membrane]]. In Gram-positive bacteria, the S-layer is attached to the peptidoglycan layer. Unique to Gram-positive bacteria is the presence of [[teichoic acid]]s in the cell wall. Some particular teichoic acids, lipoteichoic acids, have a lipid component and can assist in anchoring peptidoglycan, as the lipid component is embedded in the membrane. === Exceptions === The [[Deinococcus-Thermus]] bacteria have Gram-positive stains, although they are structurally similar to Gram-negative bacteria. == Pathogenesis == Most pathogenic bacteria in humans are gram-negative organisms. Classically, six gram-positive organisms are typically pathogenic in humans. Two of these, ''Streptococcus'' and ''Staphylococcus'', are [[cocci]] (round bacteria). The remaining organisms are bacilli (rod-shaped bacteria) and can be subdivided based on their ability to form spores. The non-spore formers are ''Corynebacterium'' and ''Listeria'', while ''Bacillus'' and ''Clostridium'' produce spores.<ref>{{cite book |title=Clinical Microbiology made ridiculously simple |last=Gladwin |first=Mark |coauthors=Bill Trattler |year=2007 |publisher=MedMaster, Inc |location=Miami, FL |isbn=978-0-940780-81-1 |pages=4-5 }}</ref> The spore-forming bacteria can again be divided based on their [[respiration]]: ''Bacillus'' is a facultative anaerobe, while ''Clostridium'' is an obligate anaerobe. ==See also== * [[Gram-negative]] * [[Carboxydothermus hydrogenoformans]] * [[:Category:Gram positive bacteria]] ==References== <!-- --------------------------------------------------------------- See http://en.wikipedia.org/wiki/Wikipedia:Footnotes for a discussion of different citation methods and how to generate footnotes using the <ref> & </ref> tags and the {{Reflist}} template -------------------------------------------------------------------- --> {{Reflist}} == External links == * {{NCBI-scienceprimer}} *[http://opm.phar.umich.edu/localization.php?localization=Bacterial%20gram-positive%20plasma%20membrane 3D structures of proteins associated with plasma membrane of Gram-positive bacteria] *[http://opm.phar.umich.edu/localization.php?localization=Bacterial%20gram-positive%20acid-fast%20cell%20wall 3D structures of proteins associated with cell wall of Gram-positive bacteria] [[Category:Staining]] [[Category:Bacteria]] [[Category:Bacteriology]] [[Category:Gram positive bacteria|*]] [[Category:Microbiology]] [[ar:جراثيم موجبة الغرام]] [[br:Gram-Ya]] [[ca:Grampositiu]] [[cs:Grampozitivní bakterie]] [[es:Bacteria Gram positiva]] [[eo:Gram-pozitivaj bakterioj]] [[fr:Gram positif]] [[ga:Gradhearfach]] [[id:Gram-positif]] [[nl:Gram-positieve bacteriën]] [[ja:グラム陽性菌]] [[no:Gram-positiv bakterie]] [[pl:Bakterie Gram-dodatnie]] [[ru:Грамположительные бактерии]] [[sl:Grampozitivna bakterija]] [[fi:Grampositiivinen bakteeri]] [[tr:Gram-pozitif]] [[uk:Грам-позитивні бактерії]] [[zh:革蘭氏陽性菌]]