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Lactose fermenters turn red or pink on MacConkey agar, and nonfermenters do not change color. The media inhibits growth of gram-positive organisms with crystal violet and bile salts, allowing for the selection and isolation of gram-negative bacteria. The media detects lactose fermentation by enteric bacteria with the pH indicator neutral red. [2]
English: MacConkey agar is a selective and differential medium used to isolate and differentiate Gram-negative bacteria, particularly those belonging to the family Enterobacteriaceae. It's primarily used to distinguish between lactose-fermenting (LF) and non-lactose-fermenting (NLF) colonies.
Klebsiella pneumoniae is a Gram-negative, non-motile, encapsulated, lactose-fermenting, facultative anaerobic, rod-shaped bacterium.It appears as a mucoid lactose fermenter on MacConkey agar.
enterocolitica strains can be identified through the use of stool samples being grown on MacConkey plates and Yersinia Selective Agar. The MacConkey plates employ the fact that Y. enterocolitica is non-lactose fermenting, and therefore show up on the plates as 2mm translucent pale colonies. On Yersinia Selective Agar plates Y.
MacConkey agar is culture medium designed to grow Gram-negative bacteria and stain them for lactose fermentation. It contains bile salts (to inhibit most Gram-positive bacteria), crystal violet dye (which also inhibits certain Gram-positive bacteria), neutral red dye (which stains microbes fermenting lactose), lactose and peptone.
Acinetobacter is a genus of Gram-negative bacteria belonging to the wider class of Gammaproteobacteria. Acinetobacter species are oxidase-negative, exhibit twitching motility, [7] and occur in pairs under magnification. They are important soil organisms, where they contribute to the mineralization of, for example, aromatic compounds.
MacConkey agar is a selective and differential medium used to differentiate between gram-negative bacteria while inhibiting the growth of gram-positive bacteria. Adding bile salts and crystal violet to the agar inhibits the growth of most gram-positive bacteria, making MacConkey agar selective.
For example, lactose fermenters turn a deep red when this pH indicator is used. Those bacteria unable to ferment lactose, often referred to as nonlactose fermenters, or NLFs for short, use the peptone in the medium. This releases ammonia, which raises the pH of the medium. Although some authors refer to NLFs as being colourless, in reality they ...