[Characteristics of the substrate specificity of the crude endogenous beta-lactamases of gram-negative bacteria].

Fifty clinical strains of Gram-negative bacteria highly resistant to beta-lactam antibiotics were studied and 9 strains producing beta-lactamases were selected. From these cultures crude beta-lactamases were isolated. The substrate specificity of these crude preparations and their sensitivity to the inhibitory effect of dicloxacillin, methicillin and carbenicillin were studied with the spectrophotometric and hydroxylamine methods. The results of the study obtained with the 2 methods were in the main comparable. 5 crude preparations had the properties of broad-spectrum beta-lactamases without pronounced selectivity with respect to any beta-lactamide. However, they differed in the level of inhibition by dicloxacillin, methicillin and carbenicillin. 4 crude preparations with a pronounced substrate profile were recommended for use in screening and investigation of natural inhibitors of beta-lactamases and beta-lactam antibiotics. These 4 preparations were cephalosporinase from Enterobacter cloaceae 975, oxacillinase from Pseudomonas aeruginosa 10380, carbenicillinase from Pseudomonas aeruginosa 10538 and beta-lactamase of the TEM type from Enterobacter cloaceae 980.