After the sample was sterilized at 80℃, Streptococcus thermophilus was added. After a period of culture, Streptococcus thermophilus began to proliferate. At this time, human metabolic substrate 2,3,5 triphenyltetrazole monochloride (TTC) was added. If the sample contains no antibiotics or the concentration of antibiotics is lower than the detection limit, Streptococcus thermophilus will continue to proliferate and reduce TTC to a red substance. On the contrary, if the sample contains bacteriostatic agent higher than the detection limit, Streptococcus thermophilus is inhibited, so the indicator TTC does not decrease and maintains its original color.

2. Inhibition method of Bacillus stearothermophilus

The culture medium is pre-added with spores of Bacillus stearothermophilus and contains pH indicator (o-cresol violet). After adding human samples and incubating, if the samples contain no antibiotics or the concentration of antibiotics is lower than the detection limit, bacterial spores will grow in the culture medium and use sugar to generate acid, and the purple of pH indicator will turn yellow. On the contrary, if the sample contains antibiotics higher than the detection limit, the bacterial spores will not grow, and the color of the pH indicator will remain unchanged, which is still purple.

3, Streptococcus damp-heat inhibition method determination method

Observing in front of a white background, when the sample in the test tube is the primary color of milk, it means that there are antibiotics in milk, which is a positive result. The red color of the sample in the test tube is negative. If the last observation is still suspicious, it is recommended to re-test.

4. Method for judging the inhibition of Bacillus stearothermophilus

Before the white background, observe the color of the culture medium in the small test tube from the side and bottom. Keep the original purple of the culture medium as a positive result, turn the culture medium into yellow or yellow-green as a negative result, and the color between the two is a suspicious result. Suspicious results should be incubated for 30 minutes before final observation. If the color of the culture medium is still between yellow and purple, it means that the concentration of antibiotics is close to the minimum detection limit of this method, and it is suggested to test again at this time.

5,4% aqueous solution of triphenyltetrazole dichloride (TTC)

raw material

2,3,5 triphenyltetrazole monochloride (TTC) 1g

Sterile distilled water 5mL

prepare

Weigh TTC, dissolve it in sterilized distilled water, put it in a brown bottle and store it at 2℃-5℃. If the solution becomes translucent white or light brown, it can't be used any more. When in use, it is diluted 5 times with sterile distilled water to become a 4% aqueous solution.

6, penicillin G reference solution

raw material

Penicillin g potassium salt 30.0 mg

Proper amount of sterile phosphate buffer solution

Proper amount of skim milk without antibiotics

Methods the standard penicillin g potassium salt was accurately weighed and dissolved in sterile phosphate buffer to make its concentration100iu/ml ~1000iu/ml. Then, the solution was diluted to 0.006IU/mL with sterile antibiotic-free skim milk, packed in sterile small test tubes and sealed for later use. Store at -20℃ for no more than 6 months.