The Charm CowSide II test is a microbial inhibition test designed for fast, simple, and affordable screening of cow's milk for antibiotic residues on the farm. The test works with raw, pasteurized, or ultra-pasteurized milk, as well as reconstituted milk powder. A color-change reaction visually identifies the presence of antimicrobial drugs commonly used in dairy production.
Cultured bacteria in the test vial react with the milk sample. If no antibiotics are present, the bacteria grow and produce acid, causing the agar to turn from purple to yellow. If antibiotics or other inhibitors are present, no color change occurs. This makes the Charm CowSide II test an efficient tool for verifying that milk is free of inhibitors before it is tanked or delivered to the dairy.
The test detects a wide range of antibiotic groups, including beta-lactams, tetracyclines, macrolides, aminoglycosides, sulfonamides, and others, often at or near EU/CODEX and US tolerance levels. The test experiences minimal interference from high fat content, somatic cell counts, or normal bacterial loads, making it suitable for daily use on the farm.
Performing a test is simple. Using the supplied disposable pipette, 100 µL of milk is added to the vial. The vial is incubated for approximately three hours at 64°C, usually in the Charm Vial Incubator or a compatible block heater. After incubation, the color is compared to the supplied interpretation card. Results should be evaluated within 30 minutes of removal from the incubator, although the color remains stable for up to 16 hours if the vial remains in the incubator after switching it off.
In the case of positive or equivocal results, the recommended retest procedure with heat treatment helps determine whether the cause is actual antibiotic residues or a heat-sensitive inhibitor, such as contamination from disinfectants. Optional positive and negative control standards are available to verify performance.
With simple operation, minimal equipment, and clear color results, the CowSide II test offers an economical and reliable way for farmers to protect milk quality, reduce the risk of rejection, and ensure confidence before the milk leaves the farm.
Table 1 . Table 1. Sensitivity – Detection range in cow's milk at 0 to 7 °C. 
