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When alpha-hemolysis (α-hemolysis) is present, the agar under the colony is light and greenish. Streptococcus pneumoniae and a group of oral streptococci (Streptococcus viridans or viridans streptococci) display alpha-hemolysis. This is sometimes called green hemolysis because of the color change in the agar.
Agar plates may also be indicator plates, in which the organisms are not selected based on growth, but are instead distinguished by a color change in some colonies, typically caused by the action of an enzyme on some compound added to the medium. [6] The plates are incubated for 12 hours up to several days, depending on the test that is performed.
DTM plate on the right showing color change after two days' growth; Microsporum canis Dermatophyte test medium (DTM) is a specialized agar used in medical mycology. [1] [2] It is based on Sabouraud's dextrose agar with added cycloheximide to inhibit saprotrophic growth, antibiotic to inhibit bacterial growth, and phenol red a pH indicator.
DNA hydrolysis is tested by growing an organism on a DNase Test Agar plate (providing nutrients and DNA) and then checking the plate for hydrolysis. The agar plate has DNA-methyl green complex, and if the organism on the agar does hydrolyze DNA then the green color fades and the colony is surrounded by a colorless zone. [25]
The increase in pH then causes color change in the bromothymol blue indicator, turning it blue. Under neutral conditions the medium remains a green color. The color change to blue is useful because growth on Simmons' citrate agar is often limited and would be hard to observe if it were not for the color change.
Chocolate agar (CHOC) or chocolate blood agar (CBA) is a nonselective, enriched growth medium used for isolation of pathogenic bacteria. [ 1 ] [ 2 ] [ 3 ] It is a variant of the blood agar plate , containing red blood cells that have been lysed by slowly heating to 80°C.
From left to right solutions of 0.1 M HCl, 3 buffer solutions of pH 3.78, 3 of pH 4.00, 3 of pH 4.62 and NaOH 0.1 M after adding different amounts of bromocresol green (more in darker solutions) In aqueous solution , bromocresol green will ionize to give the monoanionic form (yellow), that further deprotonates at higher pH to give the dianionic ...
E. coli on EMB agar. Eosin methylene blue (EMB, also known as "Levine's formulation") is a selective and differential media used for the identification of Gram-negative bacteria, [1] specifically the Enterobacteriaceae. EMB inhibits the growth of most Gram-positive bacteria. EMB is often used to confirm the presence of coliforms in a sample.