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The organism on the right produced no color, so it does not appear to be a lactose fermenter. MacConkey agar is a selective and differential culture medium for bacteria. It is designed to selectively isolate gram-negative and enteric (normally found in the intestinal tract) bacteria and differentiate them based on lactose fermentation. [1]
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.
Sorbitol-MacConkey agar is a variant of traditional MacConkey agar used in the detection of E. coli O157:H7. [1] Traditionally, MacConkey agar has been used to distinguish those bacteria that ferment lactose from those that do not.
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.
As in MacConkey agar, coliform organisms ferment the lactose, and the colonies become red. Non-lactose-fermenting organisms produce clear, colourless colonies against the faint pink background of the medium. [7] mFC medium is used in membrane filtration and contains selective and differential agents.
Most strains of Acinetobacter, except some of the A. lwoffii strain, grow well on MacConkey agar (without salt). Although officially classified as not lactose-fermenting, they are often partially lactose-fermenting when grown on MacConkey agar. They are oxidase-negative, catalase-positive, indole-negative, nonmotile, and usually nitrate-negative.
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.
The organism is also fast-growing in liquid media, and there will give the liquid an overall pink hue. On blood agar plates, the colonies are typically convex and large, with a brown pigment, and cause “greening” of the agar around the colonies. S. putrefaciens are non-lactose fermenters on MacConkey