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Bile salts are the selective ingredient, while esculin is the differential component. Enterococcus hydrolyze esculin to products that react with ferric citrate in the medium to produce insoluble iron salts, resulting in the blackening of the medium. Test results must be interpreted in conjunction with gram stain morphology.
Aesculetin forms dark brown or black complexes with ferric citrate, allowing the test to be read. The bile aesculin agar is streaked and incubated at 37 °C (99 °F) for 24 hours. The presence of a dark brown or black halo indicates that the test is positive. A positive test can occur with Enterococcus, Aerococcus, and Leuconostoc.
The plates are incubated for 12 hours up to several days, depending on the test that is performed. Commonly used types of agar plates include: Red blood cells on an agar plate are used to diagnose infection. On the left is a positive Staphylococcus infection, on the right a positive Streptococcus culture.
The catalase test tests whether a microbe produces the enzyme catalase, which catalyzes the breakdown of hydrogen peroxide. Smearing a colony sample onto a glass slide and adding a solution of hydrogen peroxide (3% H 2 O 2) will indicate whether the enzyme is present or not. Bubbling is a positive test while nothing happening is a negative ...
VRDBA, VRDB Agar, or Violet Red Bile Dextrose Agar, is a microbiological growth medium. [1] It can be used in agar plates to monitor or assess bacterial growth in the laboratory, particularly the growth of Enterobacteriaceae , for which it is selective.
When inoculated with a sample organism and allowed to incubate, the medium will change color from red to yellow to indicate that the mannite has been fermented.
Samples positive for gas production are transferred to brilliant green lactose bile broth (BLGB) to detect the ability to grow in the presence of bile and produce gas at 95 °F (35 °C) for 48 hours. The absence of gas production in 48 hours is considered a negative test for coliforms. [2]
Sabouraud agar or Sabouraud dextrose agar (SDA) is a type of agar growth medium containing peptones. [1] It is used to cultivate dermatophytes and other types of fungi , and can also grow filamentous bacteria such as Nocardia .