Production and characterization of group-specific antibodies against penicillin antibiotics

Polyclonal antibodies against penicillin antibiotics were produced in rabbits after immunization with ait ampicillin-bovine scrum 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 pencillins having the intact 6-aminopenicillanic acid (6-APA) nucleus, and was able to detect 16 other penicillins tested, whereas cephalosporin antibiotics were riot detected. Relative cross-reactivities (pencillin G = 100%) exceeding 10% were found for amoxicillin (45%), ampicillin (45%), 6-APA (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 beta-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.