What is Gram-negative?
[[Image:Gram-Cell-wall.svg|thumb|right|Gram-positive- and negative bacteria are chiefly differentiated by their [[cell wall]] structure.]] '''Gram-negative bacteria''' are [[bacteria]] that do not retain [[crystal violet]] dye in staining.<ref name=Baron>{{cite book | pmid=21413343| author = Baron S, Salton MRJ, Kim KS | chapter = Structure|title=Baron's Medical Microbiology|editor=Baron S | display-authors = etal| edition = 4th | publisher = Univ of Texas Medical Branch | year = 1996 | url = https://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mmed.section.289 | isbn = 0-9631172-1-1 }}</ref> In a Gram stain test, a counterstain, [[safranin]], is added after the crystal violet. This colours all gram-negative bacteria with a red or pink colour. This happens because an outer membrane stops the penetration of the stain. The test itself is useful in classifying two distinct types of bacteria based on the structural differences of their [[Cell wall#Bacterial cell walls|bacterial cell wall]]s. [[Gram-positive]] bacteria retain the crystal violet dye when washed in a decolourizing solution. Compared with gram-positive bacteria, gram-negative bacteria are more resistant against [[antibiotics]], because of their relatively impermeable cell wall. The [[lipopolysaccharide]] layer (LPS layer) is important.<ref name=Baron /> In humans, LPS triggers an [[innate immune response]], with [[cytokine]] production and [[immune system]] activation. [[Inflammation]] is a common result of cytokine production. [[Image:Gram negative cell wall.svg|thumb|500px|center|Gram-negative cell wall structure]] == References == {{reflist|2}} ==Other websites== * [http://opm.phar.umich.edu/localization.php?localization=Bacterial%20gram-negative%20inner%20membrane 3D structures of proteins from inner membranes of Ellie Wyithe's gram-negative bacteria] * [http://microbeid.com/Methods/gramstain.html Gram Staining Procedure and Images] {{Webarchive|url=https://web.archive.org/web/20120222214510/http://www.microbeid.com/Methods/gramstain.html |date=2012-