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The pour plate technique is the typical technique used to prepare plate count agars. Here, the inoculum is added to the molten agar before pouring the plate. The molten agar is cooled to about 45 degrees Celsius and is poured using a sterile method into a petri dish containing a specific diluted sample.
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).
The plate count method relies on bacteria growing a colony on a nutrient medium so that the colony becomes visible to the naked eye and the number of colonies on a plate can be counted. To be effective, the dilution of the original sample must be arranged so that on average between 30 and 300 colonies of the target bacterium are grown.
An agar plate being viewed in an electronic colony counter Example of a workup algorithm of possible bacterial infection in cases with no specifically requested targets (non-bacteria, mycobacteria etc.), with most common situations and agents seen in a New England community hospital setting. Different agar plates are used for different specimen ...
The traditional colony count method could be modified to measure antimicrobial activity in the 96-well plate without the need for sampling the wells and spreading surviving cells on agar plates by simply adding an equal volume of twice-concentrated broth after the two hour incubation in the low salt buffer.
The plates are left upright on the bench to dry before inversion and incubation at 37 °C for 18 – 24 hours (or appropriate incubation conditions considering the organism and agar used). Each sector is observed for growth, high concentrations will give a confluent growth over the area of the drop, or a large number of small/merged colonies.
Stab cultures are similar to agar plates, but are formed by solid agar in a test tube. Bacteria is introduced via an inoculation needle or a pipette tip being stabbed into the center of the agar. Bacteria grow in the punctured area. [11] Stab cultures are most commonly used for short-term storage or shipment of cultures.
The count represents the number of colony forming units (cfu) per g (or per ml) of the sample. A TVC is achieved by plating serial tenfold dilutions of the sample until between 30 and 300 colonies can be counted on a single plate. The reported count is the number of colonies counted multiplied by the dilution used for the counted plate