cows in field

To the NODPA Executive Director

Dear NODPA News Editor:

It is important that clarification be made about the information published recently, both on the Odairy listserv and in the September NODPA News, that stated aflatoxins, particularly gliotoxin, interfere with the Charm tests. This information is not accurate.

(Charm Sciences manufactures rapid diagnostic tests across many industries for antibiotics in milk, specifically tests for sulfonamide drugs.)

When the situation referenced in that article was unfolding, I contacted the technical services folks at Charm Sciences to discuss more fully the potential for cross-reaction to their sulfonamide assays, the Charm ROSA SULF test primarily used in milk processing plants and the Charm II SULFA test primarily used for confirmation testing in certified laboratories.

When the original email on the Odairy listserv was published, I questioned the Charm technical experts specifically about the potential cross-reactivity of mycotoxins in the sulfonamide assays and was told that they had no evidence of such cross-reactivity in these assays. Based on the claim that gliotoxin was the culprit that created the positive sulfonamide tests, the folks at Charm proactively ordered known gliotoxin and checked this specific mycotoxin component with their assays to determine if there was cross-reactivity. There was not.

Bob Salter, the Vice President of Regulatory Affairs at Charm Sciences, responded to my request for comment to the NODPA article. In his words, "There is no data that indicate Charm Sulfa Tests are interfered by mycotoxins. I am not sure where the author got this information, but it is not in literature to my knowledge, and it is not information that came from Charm Sciences Inc."

He continued, "Following the incident earlier this summer, when our technical support staff were asked specifically about the potential of a specific mycotoxin, gliotoxin, containing a sulfur molecule, causing a sulfonamide test cross reactivity, we answered that we had no evidence to believe there would be any cross reactivity from sulfur compounds or from mycotoxins; but as a follow up to the question, we purchased gliotoxin from Sigma chemical and did a cross reactivity challenge. This challenge confirmed that there is no 1000 ppb gliotoxin cross reactivity to the Charm Sulfa test."

Mr. Salter offered that the only known interference to the Charm II Sulfa test is para-amino-benzoic acid (PABA), a co-vitamin made by bacteria in yeast. PABA is not a normal constituent in milk and it does not pass through cattle rumen. When bacterial levels in milk are in excess of 3 million cfu/mL a positive Charm II Sulfa test might result. But PABA does not interfere with the Charm ROSA SULF test. His information about the Odairy event was that the milk samples in question tested positive by both Charm sulfonamide tests.

The leaps and bounds in testing and assay technologies, both cow-side and in the laboratory, creates a two edged sword – with lots of opportunity and positive potential coupled with plenty of room for misunderstanding and misinterpretation.

Ferreting out the correlations and causations in these situations can be very interesting and typically includes thinking outside the box – but also requires that we know the characteristics and limitations of the technologies that we are employing.

In my conversations with Mr. Salter he recounted several situations in which they were involved in trouble-shooting some positive milk tests in very unusual circumstances. Those fascinating case histories will be part of some further writing about cow side testing, interpretation of some of these tests and troubleshooting (perhaps unexpected) results of such testing.

Susan Beal, DVM