TESTING MILK FOR ANTIBIOTICS
Set up everything needed on a clean surface before you start. The test kit is in the white refrigerator. Turn on the incubation block to warm up. Wash and dry your hands thoroughly.
Label a test ampule containing purple agar medium for each cow being tested. You must cut (not tear) each ampule to separate it from the pack. If you tear the foil on any ampule, you must use it immediately or discard it.
Using the plastic forceps, poke a hole in the top of the ampule corresponding to the milk sample you are setting up. Be careful not to touch the end of the forceps with your hands or to touch the forceps to the agar. This avoids contaminating the test with substances that may interfere or create false positive tests.
Shake a few nutrient tablets into the bottle cap. Using the forceps, place one tablet into the ampule. If the tablet touches any surface, discard it and get a new tablet.
Attach a disposable pipette tip to the small spring syringe, being careful not to touch the end of the tip.
Shake the milk sample.
Depress the plunger of the syringe fully, dip the tip into the center of the milk sample, and allow the spring to suck up a sample of the milk. Avoid bubbles.
Squirt the sample in the test ampule.
Place the test ampule into the incubator block.
Repeat steps 1 – 8 for each sample.
Using the clock on the FAX machine as the timer, write the time the tests will be done (3 hours) on the white board above the incubator block.
Interpreting Results
If the bacteria can grow, they will metabolize the nutrient tablet and produce acid. The acid produced causes the agar to change from purple to yellow. Milk samples with enough growth inhibitor (antibiotics) to stop or slow bacterial metabolism will remain purple.
Tests that turn yellow are negative: no antibiotics
(within the limits of the test and the antibiotic).
Tests that remain purple are positive: antibiotic is present and the cow should be kept in Pen 41 and retested.
If in doubt, keep the cow in Pen 41 and retest her the next day.
