MacConkey agar - Wikipedia, the free encyclopedia
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MacConkey agar
From Wikipedia, the free encyclopedia
MacConkey agar (or McConkey agar) is a culture medium designed
to grow Gram-negative bacteria and stain them for lactose
fermentation.[1]
Contents
1 Contents
2 History
3 Uses
3.1 Lac+
3.2 Lac3.3 Slow
Macconkey agar with lactose(left)
and non-lactose(right) fermenters
4 Variant
5 See also
6 References
7 External links
Contents
It contains bile salts (to inhibit most Gram-positive bacteria, except
Enterococcus and some species of Staphylococcus i.e. Staphylococcus
aureus), crystal violet dye (which also inhibits certain Gram-positive
bacteria), neutral red dye (which stains microbes fermenting lactose),
lactose and peptone.
A MacConkey agar plate with an
active bacterial culture.
History
The medium was developed by Alfred Theodore MacConkey while
working as a bacteriologist for the Royal Commission on Sewage
Disposal.
Uses
Acting as a visual pH indicator, the agar distinguishes those Gramnegative bacteria that can ferment the sugar lactose (Lac+) from those
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MacConkey agar - Wikipedia, the free encyclopedia
that cannot (Lac-).
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Lactose
This medium is also known as an "indicator medium" and a "low
selective medium". Absence of electrolytes serves to inhibit swarming by Proteus species.
Lac+
By utilizing the lactose available in the medium, Lac+ bacteria such as Escherichia coli, Enterobacter and
Klebsiella will produce acid, which lowers the pH of the agar below 6.8 and results in the appearance of
red/pink colonies.
LacNon-Lactose fermenting bacteria such as Salmonella, Proteus species, Pseudononas aeruginosa and Shigella
cannot utilize lactose, and will use peptone instead. This forms ammonia, which raises the pH of the agar, and
leads to the formation of white/colorless colonies.
Slow
Some organisms ferment lactose slowly or weakly, and are sometimes put in their own category. These
include Serratia [2] and Citrobacter.[3]
Variant
A variant, Sorbitol-MacConkey agar, (with the addition of additional selective agents) can assist in the
isolation and differentiation of enteropathogenic E. coli serotypes such as E. coli O157:H7, by the presence of
white circular colonies that are non-sorbitol fermenting.
See also
R2a agar
References
1. ^ "tmc.edu" (http://medic.med.uth.tmc.edu/path/macconk.htm) . http://medic.med.uth.tmc.edu/path/macconk.htm.
2. ^ Luis M. De LA Maza; Pezzlo, Marie T.; Janet T. Shigei; Peterson, Ellena M. (2004). Color Atlas of Medical
Bacteriology. Washington, D.C: ASM Press. pp. 103. ISBN 1-55581-206-6.
3. ^ "Medmicro Chapter 26" (http://gsbs.utmb.edu/microbook/ch026.htm) . http://gsbs.utmb.edu/microbook/ch026.htm.
Retrieved 2008-12-11.
External links
http://en.wikipedia.org/wiki/MacConkey_agar
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MacConkey Agar Description & Formulation (http://www.microbeid.com/Media/mac.html)
Retrieved from "http://en.wikipedia.org/wiki/MacConkey_agar"
Categories: Microbiological media | Growth media
This page was last modified on 8 June 2010 at 18:48.
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