Detection of antibiotics in goats' milk: Comparison of different commercial microbial inhibitor tests developed for the testing of cows' milk

Nine microbial inhibitor tests validated for cows' milk (BR-AS Special, CMT-Copan Milk Test, Delvotest SP-NT, Delvotest T, Brilliant Black Reduction Test MRL, Charm Blue Yellow II, Charm CowSide II, Eclipse 100, Eclipse 3G) were applied to milk samples from 200 different individual goats. Interpretation of the results was based on visual and instrumental reading. Samples initially testing positive were retested and also tested after a milk pre-treatment (heat treatment, fat removal or fat removal followed by heat treatment). With instrumental reading, most microbial tests commonly used for bovine milk were suitable for goats' milk (specificity ≥95%), except for BR-AS Special, Charm Blue Yellow II and Delvotest SP-NT. However, visual reading of the results decreased the specificity, with ≥95% specificity only for CMT-Copan Milk Test, Eclipse 3G and Delvotest T. Fat removal followed by heat treatment proved the most appropriate milk treatment to reduce false positive results for almost all tests.