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    Home > Chemicals Industry > Chemical Technology > Fast counting method of Staphylococcus aureus (direct counting method)

    Fast counting method of Staphylococcus aureus (direct counting method)

    • Last Update: 2022-03-18
    • Source: Internet
    • Author: User
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    Staphylococcus aureus belongs to the genus Staphylococcus and is the main pathogenic factor that causes food-borne diseases


    The immunological method is the traditional detection method for Staphylococcus aureus.


    [Detection principle]

    PetrifiIm TM Staphylococcus aureus test piece is a pre-prepared medium system, which contains a modified Baird-Parker medium with color development function, which has strong selectivity for Staphylococcus aureus, and contains Cold water soluble gel.


    [Equipment and materials]

    Constant temperature box: (36±1)℃, (30±1)℃;

    Homogenizer (rotary knife type or flapping type) or equivalent equipment;

    Refrigerator: 2~5℃;

    pH meter or precision pH test paper;

    Magnifying glass or colony counter


    [Medium and Reagents]

    (1) Sterile physiological saline Weigh 8.


    (2) 1mol/L sodium hydroxide (NaOH) Weigh 40g NaOH and dissolve it in 1000mL distilled water


    (3) 1mol/L hydrochloric acid (HCl) pipette 90mL concentrated hydrochloric acid, dilute with distilled water to 1000mL


    (4) Petri film TM Staphylococcus aureus test piece


    (5) Petri film "Staphylococcus aureus confirmation reaction film


    [Inspection Procedure]

    See Figure 1-3


    [Sample Preparation]

    After preparing a 1:10 sample solution, aseptically adjust the pH of the sample solution to 6.


    [Inoculation]

    Make 10-fold incremental dilutions, and select appropriate 2~3 serial dilutions of sample homogenate (liquid samples may include the stock solution) to inoculate PetrifiIm TM test pieces, inoculate 2 pieces for each dilution, each 1mL


    [bring up]

    Place the test piece with the transparent side facing up, and place it horizontally in the incubator.


    [Confirmation response]

    If there is no colony growth on the above test piece or all the colonies are purple-red (typical characteristics of Staphylococcus aureus), no confirmation is needed.


    Lift the upper film, place the confirmation reaction sheet in the culture range of the test sheet, and then put the upper film down and cover it on the confirmation reaction sheet, and gently press the test sheet and the confirmation reaction sheet by sliding with your fingers, including confirmation At the edge of the reaction piece, this step can make the test piece come into close contact with the PetrifiIm TM confirmation reaction piece and remove air bubbles.


    [Result calculation and report]

    Judgment: Fuchsia colonies are directly counted as Staphylococcus aureus; when confirmation reaction sheets are needed for confirmation, count colonies with pink halos


    Colony count: count immediately after the culture is completed, you can count visually or with a colony counter, and a magnifying glass can assist the count; select a test piece with a colony of Staphylococcus aureus between 15 and 150, calculate the number of colonies, and multiply the report by the corresponding dilution factor If the number of colonies on all dilution test pieces is less than 15, then count the number of colonies on the test piece with the lowest dilution and multiply it by the dilution factor to report it; if all colonies grow on the test piece at all dilutions, multiply it by less than 1.
    Report the lowest dilution; if the number of colonies with the highest dilution is greater than 150, count the number of colonies on the test piece with the highest dilution and multiply it by the dilution
    .
    The reporting unit is expressed in CFU/g (mL)
    .

    Related links: rapid screening test for Salmonella, enterohemorrhagic Escherichia coli O157 and Listeria monocytogenes (enzyme-linked immunoassay)

     

     

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