[Bactericidal activity of aspoxicillin in an in vitro model simulating human serum levels]

Bactericidal activities of aspoxicillin (ASPC) against E. coli (2 strains) and K. pneumoniae (1 strain) were compared with those of piperacillin (PIPC) using in vitro kinetic models simulating human serum levels. In the model of intravenous injection, both drugs exhibited bactericidal action against the strains of E. coli. The activity of ASPC was found to superior to PIPC and ASPC could decrease viable cell counts from 10(7) cells/ml to 10(8) cells/ml. On the other hand, the bactericidal activity of ASPC against K. pneumoniae was weaker than that of PIPC. In the model of intravenous drip infusion, ASPC showed a high level of bactericidal activity comparable to that observed in the intravenous model against E. coli. Interestingly, the bactericidal activity of ASPC against K. pneumoniae in this model was similar to that of PIPC, though the MIC value of ASPC was higher than that of PIPC. In the intravenous model, the effects of ASPC and PIPC on the morphology of E. coli KC-14 were examined with a phase contrast microscope. Exposure to PIPC caused only an elongation of the cells, but the treatment with ASPC resulted in the formation of spheroplast-like structure of the cells, which were finally subjected to bacteriolysis.