Gram-negative

Jump to navigation Jump to search

WikiDoc Resources for Gram-negative

Articles

Most recent articles on Gram-negative

Most cited articles on Gram-negative

Review articles on Gram-negative

Articles on Gram-negative in N Eng J Med, Lancet, BMJ

Media

Powerpoint slides on Gram-negative

Images of Gram-negative

Photos of Gram-negative

Podcasts & MP3s on Gram-negative

Videos on Gram-negative

Evidence Based Medicine

Cochrane Collaboration on Gram-negative

Bandolier on Gram-negative

TRIP on Gram-negative

Clinical Trials

Ongoing Trials on Gram-negative at Clinical Trials.gov

Trial results on Gram-negative

Clinical Trials on Gram-negative at Google

Guidelines / Policies / Govt

US National Guidelines Clearinghouse on Gram-negative

NICE Guidance on Gram-negative

NHS PRODIGY Guidance

FDA on Gram-negative

CDC on Gram-negative

Books

Books on Gram-negative

News

Gram-negative in the news

Be alerted to news on Gram-negative

News trends on Gram-negative

Commentary

Blogs on Gram-negative

Definitions

Definitions of Gram-negative

Patient Resources / Community

Patient resources on Gram-negative

Discussion groups on Gram-negative

Patient Handouts on Gram-negative

Directions to Hospitals Treating Gram-negative

Risk calculators and risk factors for Gram-negative

Healthcare Provider Resources

Symptoms of Gram-negative

Causes & Risk Factors for Gram-negative

Diagnostic studies for Gram-negative

Treatment of Gram-negative

Continuing Medical Education (CME)

CME Programs on Gram-negative

International

Gram-negative en Espanol

Gram-negative en Francais

Business

Gram-negative in the Marketplace

Patents on Gram-negative

Experimental / Informatics

List of terms related to Gram-negative

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Gram-negative Pseudomonas aeruginosa bacteria (pink-red rods).

Gram-negative bacteria are those that do not retain crystal violet dye in the Gram staining protocol.[1] Gram-positive bacteria will retain the dark blue dye after an alcohol wash. In a Gram stain test, a counterstain (commonly Safranin) is added after the crystal violet, colouring all Gram-negative bacteria a red or pink colour. The test itself is useful in classifying two distinctly different types of bacteria based on structural differences in their cell walls.[2]

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, in particular the lipopolysaccharide (also known as LPS or endotoxin) layer.[1] The LPS is the trigger which the body's innate immune response receptors sense to begin a cytokine reaction. It is toxic to the host. It is this response which begins the inflammation cycle in tissues and blood vessels.

Characteristics

Gram positive and negative cell wall structure

The following characteristics are displayed by Gram-negative bacteria:

  1. Cell walls only contain a few layers of peptidoglycan (which is present in much higher levels in Gram-positive bacteria)
  2. Cells are surrounded by an outer membrane containing lipopolysaccharide (which consists of Lipid A, core polysaccharide, and O-polysaccharide) outside the peptidoglycan layer
  3. Porins exist in the outer membrane, which act like pores for particular molecules
  4. There is a space between the layers of peptidoglycan and the secondary cell membrane called the periplasmic space
  5. The S-layer is directly attached to the outer membrane, rather than the peptidoglycan
  6. If present, flagella have four supporting rings instead of two
  7. No teichoic acids or lipoteichoic acids are present
  8. Lipoproteins are attached to the polysaccharide backbone whereas in Gram-positive bacteria no lipoproteins are present
  9. Most do not sporulate (Coxiella burnetti forms spore-like structures).

Example species

The proteobacteria are a major group of Gram-negative bacteria, including Escherichia coli, Salmonella, and other Enterobacteriaceae, Pseudomonas, 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, spirochaetes, green sulfur and green non-sulfur bacteria. Crenarchaeota: Unique because most bacteria have gram-positive molecules in their capsules, it has gram-negative.

Medically relevant Gram-negative 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).

Nosocomial gram negative bacteria 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 outer membrane. This outer membrane is responsible for protecting the bacteria from several antibiotics, dyes, and detergents 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

References

  1. 1.0 1.1 Salton MJR, Kim KS (1996). Structure. in: Baron's Medical Microbiology (Baron S et al, eds.) (4th ed. ed.). Univ of Texas Medical Branch. ISBN 0-9631172-1-1.
  2. Madigan M, Martinko J (editors) (2005). Brock Biology of Microorganisms (11th ed. ed.). Prentice Hall. ISBN 0-13-144329-1.

External links

br:Gram-nann cs:Gramnegativní bakterie id:Gram-negatif it:Gram - nl:Gram-negatieve bacteriën no:Gram-negative sl:Gramnegativne bakterije fi:Gramnegatiivinen bakteeri uk:Грам-негативні бактерії


Template:WikiDoc Sources