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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] ... so it is referred to as a late-lactose fermenter.
It appears as a mucoid lactose fermenter on MacConkey agar. Although found in the normal flora of the mouth, skin, and intestines, [ 1 ] it can cause destructive changes to human and animal lungs if aspirated, specifically to the alveoli, resulting in bloody, brownish or yellow colored jelly-like sputum .
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.
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.
To determine the presence of Enterobacter in a sample, they are first grown on MacConkey agar to confirm they are lactose fermenting. [5] An indole test will differentiate Enterobacter from Escherichia, as Enterobacter are indole negative and Escherichia is positive. [5] Enterobacter are distinguished from Klebsiella because of their ...
Rapid lactose fermentation produces acids, which lower the pH. This encourages dye absorption by the colonies, which are now colored purple-black. Lactose non-fermenters may increase the pH by deamination of proteins. This ensures that the dye is not absorbed. The colonies will be colorless. Metallic green sheen of E. coli on EMB agar