[Characterization by zymograms of R factor-determined beta-lactamases: plasmids of defined and undefined...

An easy biochemical method is described, discriminating the beta-lacta-mases coded by various R factors. Electrophoretic mobility and substrate affinity of beta-lactamases were studied simultaneously for 7 different penicillins and cephalosporins. They are I like R factors assigned into different compatibility groups (N, P, com6, com7, com8, X and com 9), five R factors isolated from piglets faeces and one R factor, RU1, originated from Enterobacter aerogenes. Three electrophoretic types of beta-lactamases were determinated: 1) beta-lactamase which migrates towards the anode (enzyme coded by Bacillus cereus chromosome); 2) beta-lactamase of weak cathodic mobility (e. g. R6K); 3) beta-lactamase which migrates rapidly towards the cathode (e. g. R46, R71). Escherichia coli K12 strains synthesize a penicillinase of this third type, destroying penicillin G. The enzymatic and physicochemical properties are not modified by host bacteria, suggesting the possibility to study the plasmid in wild bacteria.