plate count

(noun)

A means to identify the number of actively growing cells in a sample.

Examples of plate count in the following topics:

  • Viable Cell Counting

    • Plate counting is used to estimate the number of viable cells that are present in a sample.
    • The plate count method or spread plate relies on bacteria growing a colony on a nutrient medium.
    • The colony becomes visible to the naked eye and the number of colonies on a plate can be counted.
    • Typical media include Plate count agar for a general count or MacConkey agar to count gram-negative bacteria such as E. coli.
    • Examples of a viable cell count are spread plates from a serial dilution of a liquid culture and pour plates.

  • Direct Counting

    • Direct counting methods include microscopic counts using a hemocytometer or a counting chamber.
    • One can also quantify the number of cells in a culture by plating a known volume of the cell culture on a petri dish with a growth medium, which is also known as a streak plate.
    • The colonies can then be counted and, based on the known volume of the culture that was spread on the plate, the cell concentration can be calculated.
    • Bacterial colony counts made from plating dilutions of bacteria are useful to estimate the strength of bacterial infections; for example, a urinary tract bacterial infection.
    • As with hemocytometers or counting chambers, cultures need to be heavily diluted prior to plating.

  • Measurements of Microbial Mass

    • An additional method for the measurement of microbial mass is the quantification of cells in a culture by plating the cells on a petri dish.
    • If the cells are efficiently distributed on the plate, it can be generally assumed that each cell will give rise to a single colony.
    • The colonies can then be counted, and based on the known volume of culture that was spread on the plate the cell concentration can be calculated.
    • As is with counting chambers, cultures usually need to be heavily diluted prior to plating; otherwise, instead of obtaining single colonies that can be counted, a so-called "lawn" will form, resulting in thousands of colonies lying over each other.
    • Additionally, plating is the slowest method of all: most microorganisms need at least 12 hours to form visible colonies.

  • Aseptic Technique, Dilution, Streaking, and Spread Plates

    • Microbiologists rely on aseptic technique, dilution, colony streaking and spread plates for day-to-day experiments.
    • The dilution of microbes is very important to get to microbes diluted enough to count on a spread plate (described later).
    • Spread plates are simply microbes spread on a media plate.
    • The glass rod is sterilized and used to spread the microbe-containing liquid uniformly on the plate.
    • Four streak plates.

  • Diagnosing Microbial Diseases

    • The most common method to isolate individual cells and produce a pure culture is to prepare a streak plate.
    • The streak plate method is a way to physically separate the microbial population, and is done by spreading the inoculate back and forth with an inoculating loop over the solid agar plate.
    • This represents four nutrient agar plates with various bacterial species represented.
    • The use of plates for microbial culture aid in identification of microbes based on size, shape, colony formation and nutrient requirement.

  • Koch and Pure Culture

    • The most common method to isolate individual microbes and produce a pure culture is to prepare a streak plate.
    • The streak plate method is a way to physically separate the microbial population and is done by spreading the inoculate back and forth with an inoculating loop over the solid agar plate.

  • Batch Culture of Bacteriophages

    • The phage can then be isolated from the resulting plaques in a lawn of bacteria on a plate.
    • The phage can then be isolated from the resulting plaques in a lawn of bacteria on a plate.

  • Culture Media

    • These agar plates provide a solid medium on which microbes may be cultured .
    • Red blood cells are used to make an agar plate.
    • Different pathogens that can use red blood cells to grow are shown on these plates.

  • HIV and AIDS

    • Stage I: HIV infection is asymptomatic with a CD4+ T cell count (also known as CD4 count) greater than 500/uL.
    • A CD4 count of less than 500/uL.
    • A CD4 count of less than 200/uL.
    • Stage 1: CD4 count ≥ 500 cells/uL and no AIDS defining conditions
    • Stage 3: CD4 count ≤ 200 cells/uL or AIDS defining conditions

  • Group B Streptococcus Colonization

    • Sometimes, before plating, enrichment of the gathered probe is performed.
    • The collected sample is streaked on a blood agar plate (vertical streaks) next to staphylococcus aureus culture (horizontal streak).