The SL3 -Lactam Test is a 3 min, receptor-based lateral flow Rapid One Step Assay (ROSA) that detects 5 of 6 -lactam drugs approved for dairy cattle in the United States. The method was evaluated through the AOAC Research Institute Performance-Tested Method program following a U.S. Food and Drug Administration protocol. Three combined lots detected penicillin G 4.2 parts per billion (ppb), ampicillin 8.7 ppb, amoxicillin 7.8 ppb, cephapirin 16.0 ppb, and ceftiofur (total metabolites) 51 ppb at least 90 of the time, with 95 confidence as determined by dose response probit analysis. These detection levels are less than safe level/tolerances but not more than 50less. Lot repeatability was within 20. Incurred residues were detected comparably or more sensitively to fortified samples due to the cumulative effect of biologically active metabolites. There were no interferences from somatic cells at 1 M/mL, bacterial cells 500 000 colony-forming units/mL, or 30 other non--lactam drugs. These performances met approval conditions of the National Conference on Interstate Milk Shipments. Ruggedness conditions were incorporated into public health procedures for annual laboratory proficiency and certification.

A qualitative 3 minute one step assay for detecting beta-lactam, sulfonamide and tetracycline antibiotics was validated following milk screening test guidelines developed by FDA-CVM, AOAC-RI and IDF. The validated 90% detection levels with 95% confidence were penicillin G 2 part per billion (ppb); amoxicillin 4 ppb; ampicillin 9 ppb; ceftiofur plus metabolites 50 ppb; cloxacillin 9 ppb; cephapirin 15 ppb; sulfadimethoxine 8 ppb; sulfamethazine 9 ppb; chlortetracycline 34 ppb; oxytetracycline 53 ppb; and tetracycline 42 ppb. Detection levels were lower than US and Canadian allowable limits for milk and were consistent with most European Maximum Residue Limits. Tests of raw commingled cows’ milk indicated a low positive error rate of < 0.3% with no interferences demonstrated by 1.08 MM/mL somatic cells, Gram – or + bacteria < 300K/mL, freeze/thawing, or non-targeted drugs. Detection of incurred residues were similar to, or more sensitive to, fortified samples. Some cross reactivity across drug families occurred in interference studies and therefore initial positive samples should be confirmed with drug family specific screening methods. The National Conference of Interstate Milk Shipments approval as a bulk tank/tanker screening test was completed in three stages for each drug family, including a tetracycline confirmation procedure to target the USA tolerance levels. Detection and robustness were found to be appropriate for multiple countries’ regulatory requirements for screening tests. The method development, validation and approval was intended to diversify and increase the verification tools for the control of the major antibiotic drug families used in managing cows’ health and welfare.