Grade investigation testing is an advisory test for samples that have received a high grade from the BactoScan test. The Grade Investigation test helps to determine if the high bacterial count is due to plant hygiene issues or mastitis related issues.
The affected milk sample is streaked onto a blood plate. The blood plate has 2 sides – one side has agar (nutrient base for bacterial growth) and the other side has agar with penicillin (an antibiotic which will inhibit bacterial growth).
The streaked plate is incubated for 24 hours. If bacteria grow on both sides of the plate, it usually indicates a plant hygiene issue. If there is growth on only the agar side of the plate, then the problem may be mastitis related.