[Studies on the in vitro bactericidal effects of cephalexin against Staphylococcus aureus (author's transl)]

The effect of cephalexin on the numbers of viable cells was studied. Two strains of Staph. aureus and 6 strains of Escherichia coli at their logarithmic phase were exposed to various concentrations (1 approximately 4 MICs) of cephalexin for 1 approximately 24 hours in vitro. The numbers of viable cells were determined by the colony-counting method during and after the exposure of cephalexin. The following results were obtained: 1. When exposure time was short (3 hours or less), the numbers of viable cells were not decreased even at the high concentration (4 MICs). And more exposure time (4 hours or more) was needed for decreasing the number of cells. 2. "Concentration" was not strong influencing factor for decreasing the numbers of cells as compared with "Exposure time". 3. From the point of decreasing the numbers of cells for 12 hours, 4-hour exposure to 1 MIC was more effective than 2-hour twice exposure at 4-hour nonexposure interval to 4 MICs of cephalexin.