Which principle is used to test for antibiotics in milk?

Testing for antibiotics in milk primarily relies on the principle that bacterial growth is inhibited when antibiotics are present. The presence of antibiotics can interfere with the normal growth of bacteria, which is fundamental in many tests conducted to determine milk quality.

When a sample of milk is tested for antibiotics, bacteria are introduced to the milk sample. If antibiotics are present, they will inhibit the growth of the bacteria, leading to little to no bacterial growth. This lack of growth is a clear indicator that antibiotics are present in the milk, signaling a potential violation of food safety standards and making the milk unsuitable for consumption.

In contrast, the other principles listed do not accurately reflect how antibiotic testing works. Enhanced bacterial growth would suggest the absence of inhibiting factors, while bacteria dying instantly would imply a different reaction that doesn't apply to antibiotic testing. Similarly, if bacterial growth remained the same, it wouldn’t indicate the presence of antibiotics, as we would expect noticeable growth or changes in response to antibiotic presence. Thus, the principle of bacterial growth inhibition is crucial in determining the safety and quality of milk regarding antibiotic contamination.