[Bactericidal effects and combined action of micronomicin with beta-lactam antibiotics against Pseudomonas aeruginosa and Escherichia coli].

Micronomicin (MCR, sagamicin) exhibited bactericidal effects at the lowest concentration among the tested aminoglycoside antibiotics, those were all bactericidal at lower concentrations than that of cefoperazone. When MCR was combined with cefoperazone (CPZ) or piperacillin (PIPC), they showed synergistic activity on checker-board method against Pseudomonas aeruginosa, and they were also synergistic against Escherichia coli when MCR was combined with cefmetazole (CMZ) and cefoxitin (CFX). MCR was synergistic against 40.7% and 44.4% of clinically isolated P. aeruginosa at the fractionary inhibitory concentration (FIC) index 0.5 or less in combination with PIPC and CPZ, respectively. All of the remaining strains of P. aeruginosa were included in the partially synergistic range of FIC index 0.5 to 1. Between MCR and CFX or CMZ, synergy was observed against 63.0% and 88.9% of clinical isolates of E. coli at the FIC index less than 1. Combined effects of MCR and PIPC or CPZ were observed investigating the growing curve of P. aeruginosa, too.