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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]
This plate is partially inhibitory to Gram (+) bacteria, and will produce a color change in the Gram (-) bacterial colonies based on lactose fermentation abilities. [12] Strong lactose fermenters will appear as dark blue/purple/black, and E.coli (which also ferments lactose) colonies will be dark colored, but will also appear to have a metallic ...
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.
Most gram-negative organisms grow well in this medium, while growth of gram-positive organisms is inhibited. [2] Coliform organisms ferment the lactose in this medium, producing a green metallic sheen (i.e. Escherichia coli), whereas non-lactose-fermenting organisms produce clear, colourless colonies, [1] i.e. Salmonella species.
It is formulated to inhibit Gram-positive bacteria, while the growth of Gram-negative bacilli is encouraged. The colonies of lactose fermenters appear yellow. It is also used to culture possible Salmonella that may be present in a food sample. Most Salmonella colonies produce a black centre on it.
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.
Citrobacter species are differentiated by their ability to convert tryptophan to indole (C. koseri is the only citrobacter to be commonly indole-positive), ferment lactose (C. koseri is a lactose fermentor), and use malonate. [3] Citrobacter shows the ability to accumulate uranium by building phosphate complexes. [4]
Hektoen enteric agar (HEK, HE or HEA) is a selective and differential agar [1] primarily used to recover Salmonella and Shigella from patient specimens. HEA contains indicators of lactose fermentation and hydrogen sulfide production; as well as inhibitors to prevent the growth of Gram-positive bacteria.