1. Principle & application scope

Staphylococcus aureuswhich is familiar to human being can produce various pathogenic substances such as enterotoxin and coagulase etc. Poisoning events caused by staphylococcus aureus have attracted more and more public attention in recent years, staphylococcus aureus count plate which adopted imported selective medium and specific enzyme chromogenic reagent is a kind of disposable rapid test product which is used to detect pathogen after cultured for 15-24 hours. This count plate can greatly simplify detection process. Staphylococcus aureus count plate which is easy to use and very convenient could be widely used in institutes of Food hygiene inspection and food factories.

Executive standard : Food safety national standard ,

                                    Food microbiological examination: staphylococcus aureus (GB 4789.10)

2. Using method

2.1 Sample preparation: Prepare the 1:10 solution by placing 25g or 25mL sample into 225mL sterile phosphate buffer solution or sterile saline. Adjust the PH to 6.0-8.0. Prepare the 1:100 solution by suck 1ml 1:10 solution with sterile pipette and add 9mL buffer solution. Accordingly, prepare solution of different dilute ratio. Replace the pipette with new aseptic one every time.

2.2 Inoculation: Select 2-3 appropriate dilution ratio to do the test for ordinary food. Place the count plate onto sterile experiment table, uncover the film on the surface. Suck 1mL solution with sterile pipette , and then drop it slowly and evenly onto the count plate, cover the film gently and stand it for 10s to let the medium solidify. Inoculate two count plate for each diluted sample solution, and at the meantime do a blank control

2.3 Culture: Pile up the count plates and place them in the original package and seal them well . Put the packages in the incubator with transparent side up. The quantity of superimposed count plates is not more than 12. The temperature of culture is 36℃±1℃,and the time of culture is 15-24h.

3. Results

Colony of staphylococcus aureus would show purplish red while other colonies would show blue after the culture. The sample shows positive result should be veritified by other detection methods or take the sample to do at least one more test using staphylococcus aureus count plate.

4. Counting method and report

4.1 Select the quantity of colony between 20 and 200 to do the counting .

4.2 If the colony quantity of two serial different dilute ration is both between 20 and 200, multiply the average quantity of them by corresponding dilution multiple as the result that the quantity of staphylococcus aureus in per milliliter or gram sample .

4.3 If the quantity of colony on all the dilution ratio count plates is less than 20CFU, multiply the average quantity of  coliform on minimum dilution multiple by minimum dilution multiple as report data. If there is not any colony growing on all different dilution ratio count plates,  report the result in terms of less than one multiplied  by minimum dilution multiple.

4.4 If the quantity of colony of all the different dilution ratio count plates is more than 200CFU, multiply the average quantity on the maximum dilution multiple count plates by maximum dilution multiple as report data. Or convert the quantity of colonies in one or two representative square to quantity of colony of each square ,and then multiply quantity of colony in each square by 20 as report data.

Use CFU/mL or CFU/g as report unit.

5. Additional explanatory note

5.1This kind of count plate play a very important role in improving the ability of sanitary executive department for handling public sanitary emergent issues.

5.2 It is proved by Shandong Province Disease Preventing and Controlling Centre that when the quantity of staphylococcus aureus is between 0 and 9, it can be detected by count plates and blood plate. So staphylococcus aureus count plate complies with the demand of pathogen detection, and it can be applied to the detection of staphylococcus aureus.

5.3 Staphylococcus aureus count plate has high sensitivity and specificity. The lower limit for testing is 3CFU/mL.There is no obvious difference when Comparing staphylococcus aureus count plate  with nutrient agar counting and Baird-Parker culture counting & chromogenic agent counting.

5.4 Dispose the used count plate timely according to biology safety waste treatment rule because there are live bacterium on them.