Production and characterization of group‐specific antibodies against penicillin antibiotics

Polyclonal antibodies against penicillin antibiotics were produced in rabbits after immunization with an ampicillin‐bovine serum albumin conjugate. The antibodies were tested in a competitive direct enzyme immunoassay (EIA) using an ampicillin‐horseradish peroxidase conjugate as the labelled antigen and penicillin G as the reference antibiotic. The 50% inhibition concentration for penicillin G was 12 ng ml−1. This penicillin EIA showed broad group‐specificity for penicillins having the intact 6‐aminopenicillanic acid (6‐APA) nucleus, and was able to detect 16 other penicillins tested, whereas cephalosporin antibiotics were not detected. Relative cross‐reactivities (penicillin G = 100%) exceeding 10% were found for amoxicillin (45%), ampicillin (45%), 6–8 (12%), azlocillin (110%), carbenicillin (39%), cloxacillin (49%), dicloxacillin (57%), epicillin (23%), metampicillin (130%), methicillin (32%), oxacillin (98%), penicillin V (160%), pheneticillin (68%), piperacillin (26%) and ticarcillin (110%). After alkaline hydrolysis of the ß‐lactam ring, the corresponding penicilloyl derivatives of these antibiotics completely lost cross‐reactivity in the test system. Therefore, the antibodies described here primarily detect the intact 6‐APA nucleus having any carboxylamide side chain.