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Because the appearance of microbial colonies changes as they grow, colonial morphology is examined at a specific time after the plate is inoculated. Usually, the plate is read at 18–24 hours post-inoculation, [1]: 163 but times may differ for slower-growing organisms like fungi.
Blood agar plates (BAPs) contain mammalian blood (usually sheep or horse), typically at a 5–10% concentration. BAPs are enriched, and differential media is used to isolate fastidious organisms and detect hemolytic activity. β-Hemolytic activity will show lysis and complete digestion of red blood cell contents surrounding a colony.
Once a plate has been successfully prepared, plate count agar cells will grow into colonies which can be sufficiently isolated to determine the original cell type. The colony-forming unit (CFU) is an appropriate description of the colony's origin. In plate counts, colonies are counted, but the count is usually recorded in CFU.
Colony-forming units are used to quantify results in many microbiological plating and counting methods, including: The pour plate method wherein the sample is suspended in a Petri dish using molten agar cooled to approximately 40–45 °C (just above the point of solidification to minimize heat-induced cell death).
An agar plate – an example of a bacterial growth medium*: Specifically, it is a streak plate; the orange lines and dots are formed by bacterial colonies.. A growth medium or culture medium is a solid, liquid, or semi-solid designed to support the growth of a population of microorganisms or cells via the process of cell proliferation [1] or small plants like the moss Physcomitrella patens. [2]
Negative selection through replica plating to screen for ampicillin sensitive colonies. Replica plating is a microbiological technique in which one or more secondary Petri plates containing different solid (agar-based) selective growth media (lacking nutrients or containing chemical growth inhibitors such as antibiotics) are inoculated with the same colonies of microorganisms from a primary ...
Chocolate agar showing Francisella tularensis colonies Comparison of two culture media types used to grow Neisseria gonorrhoeae bacteria. Known as overgrowth, the nonselective chocolate agar medium on the left, due to its composition, allowed for the growth of organismal colonies other than those of N. gonorrhoeae, while the selective Thayer–Martin medium on the right, containing ...
The inoculation loop is then dragged across the surface of the agar back and forth in a zigzag motion until approximately 30% of the plate has been covered. The loop then is re-sterilized and the plate is turned 90 degrees. Starting in the previously streaked section, the loop is dragged through it two to three times continuing the zigzag pattern.