Gram-negative bacteria 12937 223215704 2008-07-03T02:31:13Z Jonny-mt 1514772 ja interwiki [[Image:Pseudomonas aeruginosa Gram.jpg|thumb|right|300px|Gram-negative ''[[Pseudomonas aeruginosa]]'' bacteria (pink-red rods).]] '''Gram-negative bacteria''' are those [[bacteria]] that do not retain [[crystal violet]] dye in the [[Gram staining]] protocol.<ref name=Baron>{{cite book | author = Salton MJR, Kim KS | title = Structure. ''in:'' Baron's Medical Microbiology ''(Baron S ''et al'', eds.)| edition = 4th ed. | publisher = Univ of Texas Medical Branch | year = 1996 | url = http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mmed.section.289 | isbn = 0-9631172-1-1 }}</ref> [[Gram-positive bacteria]] will retain the crystal violet dye when washed in a decolorizing solution. In a Gram stain test, a [[counterstain]] (commonly [[safranin]]) is added after the crystal violet, coloring all Gram-negative bacteria a red or pink color. The test itself is useful in classifying two distinct types of bacteria based on structural differences in their [[cell wall]]s. Many species of Gram-negative bacteria are [[pathogen]]ic, meaning they can cause disease in a host organism. This pathogenic capability is usually associated with certain components of Gram-negative cell walls, in particular the [[lipopolysaccharide]] (also known as LPS or [[endotoxin]]) layer.<ref name=Baron /> In humans, LPS triggers an [[innate immune response]] characterized by [[cytokine]] production and [[immune system]] activation. [[Inflammation]] is a common result of cytokine production, which can also produce host toxicity. ==Characteristics== [[Image:Gram negative cell wall.svg|thumb|350px|right|Structure of gram-negative cell wall]] [[Image:Gram-Cell-wall.svg|thumb|300px|Gram-positive and -negative bacteria are chiefly differentiated by their [[cell wall]] structure.]] The following characteristics are displayed by Gram-negative bacteria: #Cytoplasmic membrane #Thin [[peptidoglycan]] layer (which is present in much higher levels in Gram-positive bacteria) #[[Outer membrane]] containing [[lipopolysaccharide]] (LPS, which consists of [[lipid A]], core polysaccharide, and [[O antigen]]) outside the peptidoglycan layer #[[Porin (protein)|Porin]]s exist in the outer membrane, which act like pores for particular molecules #There is a space between the layers of peptidoglycan and the secondary cell membrane called the [[periplasmic space]] #The [[S-layer]] is directly attached to the outer membrane, rather than the peptidoglycan #If present, [[flagella]] have four supporting rings instead of two #No [[teichoic acid]]s or [[lipoteichoic acid]]s are present #[[Lipoprotein]]s are attached to the polysaccharide backbone whereas in Gram-positive bacteria no lipoproteins are present #Most do not sporulate (''Coxiella burnetti'', which produces spore-like structures, is a notable exception) ==Example species== The [[proteobacteria]] are a major group of Gram-negative bacteria, including ''[[Escherichia coli]]'', ''[[Salmonella]]'', and other [[Enterobacteriaceae]], ''[[Pseudomonas]]'', ''[[Moraxella catarrhalis|Moraxella]]'', ''[[Helicobacter]]'', ''Stenotrophomonas'', ''[[Bdellovibrio]]'', [[acetic acid bacteria]], ''[[Legionella]]'' and alpha-proteobacteria as ''[[Wolbachia]]'' and many others. Other notable groups of Gram-negative bacteria include the [[cyanobacteria]], [[spirochaete]]s, [[green sulfur bacteria|green sulfur]] and [[green non-sulfur bacteria|green non-sulfur]] bacteria. Medically relevant Gram-negative [[Coccus|cocci]] include three organisms, which cause a [[sexually transmitted disease]] (''[[Neisseria gonorrhoeae]]''), a [[meningitis]] (''[[Neisseria meningitidis]]''), and respiratory symptoms (''[[Moraxella catarrhalis]]''). Medically relevant Gram-negative [[bacilli]] include a multitude of species. Some of them primarily cause respiratory problems (''[[Hemophilus influenzae]]'', ''[[Klebsiella pneumoniae]]'', ''[[Legionella pneumophila]]'', ''[[Pseudomonas aeruginosa]]''), primarily urinary problems (''[[Escherichia coli]]'', ''[[Proteus mirabilis]]'', ''[[Enterobacter]] cloacae'', ''[[Serratia marcescens]]''), and primarily gastrointestinal problems (''[[Helicobacter pylori]]'', ''[[Salmonella enteritidis]]'', ''[[Salmonella typhi]]''). Gram negative bacteria associated with [[nosocomial infection]]s include ''[[Acinetobacter baumanii]]'', which cause bacteremia, secondary meningitis, and ventilator-associated pneumonia in intensive care units of hospital establishments. ==Medical treatment== One of the several unique characteristics of Gram-negative bacteria is the structure of the [[outer membrane]]. The outer leaflet of the membrane comprises a complex [[lipopolysaccharide]] whose [[lipid]] portion acts as an [[endotoxin]]. If endotoxin enters the circulatory system it causes a toxic reaction with the sufferer having a high temperature and respiration rate and a low blood pressure. This may lead to endotoxic shock, which may be fatal. This outer membrane protects the bacteria from several [[antibiotic]]s, dyes, and [[detergent]]s which would normally damage the inner membrane or cell wall ([[peptidoglycan]]). The outer membrane provides these bacteria with resistance to [[lysozyme]] and [[penicillin]]. Fortunately, alternative medicinal treatments such as lysozyme with [[EDTA]], and the antibiotic [[ampicillin]] have been developed to combat the protective outer membrane of some pathogenic Gram-negative organisms. Other drugs can be used, namely [[chloramphenicol]], [[streptomycin]], and [[nalidixic acid]]. ==See also== * [[Gram-positive bacteria]] * [[Braun's lipoprotein]] * [[:Category:Gram negative bacteria]] ==References== {{Reflist}} <div class="references-small"> * {{NCBI-scienceprimer}} </div> ==External links== *[http://opm.phar.umich.edu/localization.php?localization=Bacterial%20gram-negative%20inner%20membrane 3D structures of proteins from inner membranes of Gram-negative bacteria] [[Category:Gram negative bacteria|*]] [[Category:Staining]] [[Category:Bacteriology]] [[Category:Microbiology]] [[ar:جراثيم سالبة الغرام]] [[br:Gram-nann]] [[cs:Gramnegativní bakterie]] [[es:Bacteria Gram negativa]] [[eo:Gram-negativa]] [[fr:Gram négatif]] [[id:Gram-negatif]] [[ja:グラム陰性菌]] [[nl:Gram-negatieve bacteriën]] [[no:Gram-negativ bakterie]] [[pl:Bakterie Gram-ujemne]] [[ru:Грамотрицательные бактерии]] [[sl:Gramnegativna bakterija]] [[fi:Gramnegatiivinen bakteeri]] [[vi:Gram âm]] [[uk:Грам-негативні бактерії]] [[zh:革蘭氏陰性菌]]