Bacteriological investigations with beta-lactamase inhibitors.

MIC's of beta-lactamase producing strains of P. aeruginosa, E. coli, P. vulgaris, P. rettgeri, E. cloacae, K. pneumoniae, S. marcescens are determined against piperacillin and in the case of S. aureus against amoxycillin and penicillin G. All the strains studied were resistant to these antibiotics. Their MIC's were determined in the combination with different concentrations (2, 5, 10 mg/l) of clavulanic acid and penicillanic acid sulfone respectively. The combination of piperacillin and clavulanic acid acts synergisticly against Klebsiella sp., indolpositive Proteus sp., and E. coli. Penicillanic acid sulfone was less active than clavulanic acid apart from indolpositive Proteus sp. Against S. aureus however both inhibitors showed the same synergistic efficacy. In detail both inhibitors are very active against constitutive penicillinase, they also exhibited a good activity against Type OXA-2, OXA-3 and SHV-1 beta-lactamase; they were less active to Type TEM-1 and OXA-1 enzyme and did not work against Type Ib, TEM-2 and Type IV beta-lactamase. In investigations using the biophotometer it could be demonstrated that the beta-lactamase inhibitor and the penicillin should be given simultaneously in order to obtain an optimal synergistic effect.