Dictionary » G » Gram-negative bacteria

Gram-negative bacteria

Definition

noun, singular: gram-negative bacterium

A group of bacteria that takes the color of the counterstain in Gram's method


Supplement

Gram staining is a useful and quick laboratory procedure to know whether a bacterial cell is gram-positive or gram-negative. Gram-positive bacterial cells will appear violet (from the crystal violet dye) whereas gram-negative bacterial cells will appear pink (usually from the safranin dye) when viewed under the microscope after gram staining. Initially, all bacterial cells are violet in colour from the initial dye treatment however some cells will lose the stain following decolorization and counterstaining with safranin. Other cells though will retain the violet stain. Those that lose the violet color and take the counterstain are called gram-negative bacteria. Those that retain the violet color after the procedure are called gram-positive bacteria.

Gram-negative bacteria are able to take the color of the counterstain because their thinner cell walls allow the acetone-alcohol to wash out the initial stain. Gram-positive bacteria, on the other hand, have thick cell walls that resist decolorization and counterstaining in Gram's method.


Examples of bacteria that are gram-negative are Escherichia coli, Salmonella spp., Neisseria spp., Shigella spp., Hemophilus influenzae, Klebsiella pneumoniae, Legionella pneumophila, Pseudomonas aeruginosa, etc.


Compare:

See also:


Please contribute to this project, if you have more information about this term feel free to edit this page



Results from our forum


How is Mycoplasma a gram positive bacteria

... and relatives in the phylum Firmicutes, consisting of low G+C Gram-positive bacteria such as Clostridium, Lactobacillus, and Streptococcus based on 16S rRNA gene analysis.

See entire post
by erangasts2
Thu Aug 14, 2014 12:25 am
 
Forum: Microbiology
Topic: How is Mycoplasma a gram positive bacteria
Replies: 2
Views: 4113

Recommendations for Bacteria Detection?

... to do a field test on, say, a lake or puddle, to check the number of bacteria present in the water. I'm not as interested in particular species ... am in obtaining some idea of "bacteria density" or parts per gram. I'm not sure if it matters, but the water may be contaminated with ...

See entire post
by lodestone25
Sun Jul 27, 2014 6:20 pm
 
Forum: Microbiology
Topic: Recommendations for Bacteria Detection?
Replies: 4
Views: 1415

Using oxidizing agents in gram stain

... happen if I replaced iodine with another oxidizing agent during the gram staining process ? So far I know that the purpose of the iodine is to ... complex with the crystal violet in order to enable the cell wall of the bacteria to retain the dye but certainly there must be other oxidizing agents ...

See entire post
by ccBiologist
Sun Sep 22, 2013 2:44 pm
 
Forum: Microbiology
Topic: Using oxidizing agents in gram stain
Replies: 1
Views: 1772

Re: Bacteremia in humans

PS: Just realized SA is a Biosafety level 2 bacteria, so I am left with no common, Biosafety-level 1 gram positive bacteria to test! Which one should I use then?

See entire post
by trivedv
Fri May 03, 2013 7:31 am
 
Forum: Human Biology
Topic: Bacteremia in humans
Replies: 1
Views: 1680

Help! "Unknown Bacteria" I have no idea where to look =T

Hi, I have been having a hard time figuring out my unknown bacteria. I honestly thought all of my test results added up to Staphylococcus Aureus, but my oxidase test read positive. My results were: 1. Gram- + 2. Morph- Coccus, cluster 3. Lactose fermentation- acid, yellow + 4. Gelatin ...

See entire post
by stephanie1234
Mon Dec 03, 2012 4:44 am
 
Forum: Microbiology
Topic: Help! "Unknown Bacteria" I have no idea where to look =T
Replies: 1
Views: 3493
View all matching forum results

This page was last modified 00:42, 30 November 2014. This page has been accessed 6,583 times. 
What links here | Related changes | Permanent link