Determination of penicillin and benzylpenicilloic acid in goat milk by enzyme immunoassays

A generic enzyme immunoassay (EIA) for penicillins containing the intact penam nucleus (PEN EIA), and an EIA for penicillin G derivative after alkaline hydrolysis of the betalactam ring (benzylpenicilloic acid, BPO EIA) were used to analyse raw goat milk. The detection limit for penicillin G in the PEN EIA was at 0.2-0.4 ng/ml, the recoveries in artificially contaminated goat milk samples (2-32 ng/ml) were at 90-140% (RSD 25-37%). The detection limit for hydrolysed penicillin G in the BPO EIA was at 1-2 ng/ml, the recovery in artificially contaminated goat milk (4-16 ng/ml) was at 95-123% (RSD 12-30%). A total of 577 goat milk samples (composite samples) collected from 13 goat milk farms in Hesse, Germany, were analysed for penicillins. Nine samples were positive in the PEN EIA, but at low levels (1 ng/ml to <4 ng/ml) in seven samples. One sample was positive at a level of 7 ng/ml, and also contained BPO at a concentration of 4.6 ng/ml. One sample yielded extremely high concentration levels in the PEN EIA (mean: 80.000 ng/ml) and in the BPO EIA (mean: 30.000 ng/ml). The relatively high levels of BPO indicate that penicillin G was used by parenteral but not intramammary application. The results show that the immunochemical methods are applicable to analyse goat milk, and that penicillin G may occasionally occur in goat milk samples in Hesse.