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This is sometimes called green hemolysis because of the color change in the agar. Other synonymous terms are incomplete hemolysis and partial hemolysis . Alpha-hemolysis is caused by the bacteria's production of hydrogen peroxide , which oxidizes hemoglobin and produces the green oxidized derivative methemoglobin .
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.
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.
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.
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.
Streptococcus pneumoniae: small colonies with raised edges displaying alpha-hemolysis on blood agar [8]: 223 Proteus sp. : swarming behaviour on blood agar [ 1 ] : 167 Serratia marcescens : red pigmentation: although considered characteristic of the species, only about 10% of specimens produce this pigment [ 8 ] : 236
If the area of inoculation turns dark-blue to maroon to almost black, then the result is positive. If a color change does not occur within three minutes, the result is negative. In alternative manner, live bacteria cultivated on trypticase soy agar plates may be prepared using sterile technique with a single-line streak inoculation. The ...