Coliform detecting board

1. Principle & application scope

Coliform is one of the crucial indexes to evaluate the quality of food hygiene. It has been widely used for the detection of food hygiene. Coliform mostly exist in feces of warm-blooded animals and the place that contaminated by feces. The quantity of coliform indicates the level of food contamination during the process of food production. Coliform detecting board consists of selective medium, specific enzyme chromogenic agent and macromolecule bibulous gel. This product is suitable for counting the quantity of coliform in food, milk, cold drinks, condiments and other raw materials; also it’s suitable for hygiene detection of instrument surface.

Executive standard: National Food Safety Standard, Microbiological Examination of Food Hygiene, Enumeration of Coliform (GB/T 4789.3);

Rapid Enumeration of Coliforms and Escherichia Coli in Foods—Petrifilm^TM li/Coliform Detecting Board Method (SN/T 1896)

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. According to the pollution level of sample, prepare solutions of tenfold increasing dilution ratios if necessary.

2.2 Inoculation: Select 2 or 3 dilution ratio solutions to do the test for ordinary sample, while for liquid sample which has little coliform (e.g. pure water and mineral water) directly suck the raw liquid to do the test. Place the detecting board on the flat experiment table. Uncover the upper film of the detecting board. Suck 1mL solution with sterile pipette, and then drop it slowly and evenly onto the detecting board. Then cover the film quickly and shake the detecting board horizontally to let the solution be adsorbed by the filter paper. Stand for 10s until the solution is adsorbed completely. Inoculate two count plates for each dilution ratio. At the same time do a blank control.

2.3 Culture: Superimpose the detecting boards together; place them upside down in the incubator for 15-24 hours at the temperature of 36℃±1℃.

3. Results

Coliform colony shows blue on the detecting board after cultivation. Select the detecting boards which the coliform quantity is between 15 CFU and 150 CFU to do the counting. Multiply the coliform average of two detecting boards by the dilution multiple as result data. If the coliform quantity of all the dilution ratios is less than 15CFU, multiply the coliform average of the minimum dilution multiple detecting boards by the dilution multiple as result data. If there is not any coliform on all the detecting boards, report the result in terms of less than 1 multiply the minimum dilution multiple as result data; If the coliform quantity of all the dilution ratio detecting boards are more than 150CFU, count a half or a quarter of the coliform number on the maximum dilution multiple detecting boards, then multiply it by 2 or 4 to get the result data.

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

4. Additional explanatory note

4.1 Coliform detecting board can shorten the detecting time, and the results are consistent with the traditional method, the coincidence rate reaches 90%.

4.2 The PH value of sample solution should be between 6.5 and 7.5, adjust the PH value with 1mol/L NaOH or 1mol/L HCL if necessary.

Dispose the used detecting boards timely according to the biology safety waste treatment rule, because there are live bacteria on them.