[Distinction between beta-lactamases of immunotypes 1 or 2 using a new beta-lactam antbiotic (author's transl)].

The resistance of Gram negative bacteria to ampicillin and carbenicillin is often associated with the presence of plasmidic transferable beta-lactamase (class III of Richmond and Sykes). Using immunological and physico-chemical tests, two sub-classes have been identified. The sensitivity of Escherichia coli K12 with plasmid P111 (immunotype 1) or plasmid P453 (immunotype 2) determined by means of the minimal inhibitory concentrations, contrasts significantly with a new beta-lactam antibiotic, X-587. Study of the kinetic constants (Km, Vmax) of the beta-lactamases confirms and explains this difference. Thus we have a simple and rapid method for differentiation of these 2 types of enzymes.