Cephalexin residue detection in milk and beef by ELISA and colloidal gold based one-step strip assay.
An evaluation of a rapid enzyme-linked immunosorbent assay (ELISA) and colloidal gold based one-step strip assay for cephalexin (CEX) residue detection in milk and beef is described. A monoclonal antibody (mAb) against CEX was produced using cephalexin-bovine serum albumin (CEX-BSA) conjugate as the immunogen, which exhibited no cross-reactivity with applied chemicals in the studied concentration range. The detection limit of rapid ELISA was calculated as 0.39 microg/kg in PBS and 19.5 microg/kg in beef and milk, which was quite lower than the European Union Maximum Residue Limit (MRL) of 100 microg/kg in milk and 200 microg/kg in muscle. Spiked samples were detected with a mean recovery of 82.8-124% and coefficient of variation of 4.88-25%, which indicated a good agreement with the spiked concentration. Accuracy and reproducibility were determined using spiked samples with four different final concentrations of 1, 2, 5, and 10 microg/kg of CEX (n = 7). Mean intra-assay variation of 6.67% and inter-assay variation of 10.66% were obtained. In contrast, the strip test for CEX had a visual detection limit of 0.5 microg/kg, which could be evaluated within 3-10 min. However, positive samples should be further quantified by more sensitive and accurate competitive indirect ELISA method. In conclusion, the described strip test is rapid, simple, and cost-effective as well as sensitive and specific enough for reliable and accurate on-site screening.
Chen
Liben
L
College of Veterinary Medicine, China Agricultural University, Beijing, China.
Wang
Zhengfang
Z
Ferreri
Miro
M
Su
Jingliang
J
Han
Bo
B
D000818:Animals; D000900:Anti-Bacterial Agents / Q000032:analysis*; D002417:Cattle; D002506:Cephalexin / Q000032:analysis*; D004350:Drug Residues / Q000032:analysis*; D004797:Enzyme-Linked Immunosorbent Assay / Q000191:economics / Q000379:methods*; D017979:Gold Colloid / Q000737:chemistry; D008460:Meat / Q000032:analysis*; D008892:Milk / Q000737:chemistry*; D012680:Sensitivity and Specificity
D000900:Anti-Bacterial Agents; D017979:Gold Colloid; D002506:Cephalexin