[The in vitro effect of a combination of sulbactam with cephalothin and cefazolin on strains of Escherichia coli and Proteus mirabilis which produce beta lactamase].

The effect of the combination of sulbactam, cephalothin, and cephazolin was studied in vitro on 88 strains of E. coli and 11 strains of P. mirabilis producing beta-lactamases. Quantitative susceptibility of the tested strains to cephalothin was examined by the disk dilution method and the effect of the combinations with sulbactam by the micromethod. The production of beta-lactamases was determined by the qualitative test with the chromogenic substrate PODAC. Of the total number of 160 E. coli strains beta-lactamases were established in 53.3% of the strains. Of the 47 P. mirabilis strains 23.4% were found to produce beta-lactamases. The effect of the combinations with sulbactam was assessed as synergistic, additive, indifferent or antagonistic. In the combination of sulbactam in the concentration of 16.0 mg/l with cephalothin and cephazolin a higher rate of synergistic and additive effect was recorded on both strains. In none of the combinations did sulbactam exert an antagonistic effect.