Gram-negative

Gram-negative bacteriaare those not stained dark blue or violet by Gram staining. On most Gram-stain preparations, Gram-negative organisms will be counterstainedand appear red or pink.

The difference lies in the cell wallof the two types of bacteria; in contrast to most Gram-positivebacteria, Gram-negative bacteria have only a few layers of peptidoglycanand a secondary cell membrane made primarily of lipopolysaccharide. The space between the layers of peptidoglycan and the secondary cell membrane is called periplasmatic space. 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 peptidoglycanlayer.

Many species of Gram-negative bacteria are pathogenic, meaning they can cause disease in a host organism. This pathogenic capability is usually associated with certain components of Gram-negative cell walls, particularly the lipopolysaccharide(endotoxin) layer.

The proteobacteriaare a major group of Gram-negative bacteria, including for instance Escherichia coli, Salmonella, and other Enterobacteriaceae, Pseudomonas, Moraxella, Helicobacter, Stenotrophomonas, Bdellovibrio, acetic acid bacteria, Legionella and a great many others. Other notable groups of Gram-negative bacteria include the cyanobacteria, spirochaetes, green sulfurand green non-sulfurbacteria.

Two major subclassifications of Gram-negative bacteria are Gram-negative cocci and Gram-negative rods (bacilli), which they owe to their appearance under a microscope. Their shape has implications for medical antibacterial therapy.

Medically relevant Gram-negative cocci include 3 organisms, which cause a sexually transmitted disease (Neisseria gonorrhea), a meningitis (Neisseria meningitidis), and respiratory symptoms (Moraxella catarrhalis).

Medically relevant Gram-negative bacilli include a multitude of species. Some of them cause primarily 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).

The Gram-negative outer membrane; which contains an endotoxin LPS, blocks antibiotics, dyes, and detergents protecting the sensitive inner membrane and cell wall. Therefore Gram-negative bacteria are resistant to lysozyme and penicillin attack.

References

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• This article contains material from the Science Primer published by the NCBI, which, as a US government publication, is in the public domainat http://www.ncbi.nlm.nih.gov/About/disclaimer.html.cs:Gramnegativní bakterie

es:Bacteria Gram negativa fr:Gram négatif nl:Gram-negatief pl:G- zh:??????

This article is licensed under the GNU Free Documentation License.
It uses material from the http://en.wikipedia.org/wiki/Gram-negative Wikipedia article Gram-negative.