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]]