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Plate count agar (PCA), also called standard methods agar (SMA), is a microbiological growth medium commonly used to assess or to monitor "total" or viable bacterial growth of a sample. PCA is not a selective medium. The total number of living aerobic bacteria can be
The spread plate method wherein the sample (in a small volume) is spread across the surface of a nutrient agar plate and allowed to dry before incubation for counting. [11] The membrane filter method wherein the sample is filtered through a membrane filter, then the filter placed on the surface of a nutrient agar plate.
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.
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 laboratory procedure involves making serial dilutions of the sample (1:10, 1:100, 1:1000, etc.) in sterile water and cultivating these on nutrient agar in a dish that is sealed and incubated. Typical media include plate count agar for a general count or MacConkey agar to count Gram-negative bacteria such as E. coli. Typically one set of ...
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.
[1]: 167–8 Bacteria that produce capsules often have a slimy (mucoid) consistency. [2]: 495 When certain microorganisms are grown on blood agar, they may digest the blood in the medium, causing visible hemolysis (destruction of red blood cells) on the agar plate. In colonial morphology, hemolysis is classified into three types: alpha-, beta ...
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