In vivo significance of the inoculum effect of antibiotics onEscherichia coli

Abstract

The minimum dosage of antibiotics which reduced mortality in rats intraperitoneally inoculated with anEscherichia coli isolate was determined. Low mortality rates (0–10%) were obtained when antibiotics with minimal or no inoculum effect (cefoxitin, cefmetazole and gentamicin) were administered to yield serum levels 3 to 20 times the MIC, while antibiotics with a pronounced inoculum effect (cefotaxime and aztreonam) had to be administered to yield serum levels 200 to 1,000 times the MIC determined with a standard (low) inoculum. Thus, it seems that the inoculum effect observed in vitro with some antibiotics forEscherichia coli may have clinical significance.