Evaluation and validation according to international standards of the Delvotest ® SP-NT screening assay for antimicrobial drugs in milk

Two new microbial inhibition assays for the screening of antibacterial substances in milk have been validated in accordance with the ISO/IDF 183 international standard. The detection limits for the 10 antimicrobial substances (penicillin, ampicillin, amoxicillin, cephapirin, ceftiofur, cloxacillin, sulphadiazine, oxytetracycline, neomycin and erythromycin) tested by the Delvotest ® SP-NT (sulphur-penicillin test no tablet) (ampoule and multi-plate formats) were found to be comparable with the European (EU) maximum residue limits. Sample measurement end-points were determined visually and by the Delvo ®Scan system. The Delvo ®Scan was effective at discriminating between matrix effects and a residue of an antimicrobial substance when present in milk at concentrations close to the lowest detected screening level. Both test formats were found to be robust and unaffected by a variety of procedural changes (e.g., sample incubation time, test volume). They were also found to be applicable for screening of milk with a range of fat contents and milk with raised somatic cell count.