Iodometric assay method for beta-lactamase with various beta-lactam antibiotics as substrates.

The rapid fixed-time assay for penicillinase was modified for measuring beta-lactamase activity with twelve substrates, i.e., benzylpenicillin, ampicillin, cloxacillin, methicillin, carbenicillin, cefazolin, cephalothin, cephaloglycin, cephalexin, cephalosporin C, 7-aminocephalosporanic acid, and cefoxitin. The method depends upon the reduction of iodine by the hydrolyzed substrate. Determined experimentally, 1 mol of hydrolyzed penicillins consumed 3.4 to 4.0 mol of iodine (I(2)). Iodine consumption of hydrolyzed cephalosporins varied widely from 1.7 for cephalothin to 3.7 for cefazolin. The method is useful for routine assay of beta-lactamase activity with various substrates.