Assessment of Timed Bacteriostatic and Bactericidal Activities of Cephalothin against Gram-Positive and Gram-Negative Bacteria

Abstract

The comparative bacteriostatic and bactericidal activities of cephalothin were assessed in broth medium with special reference to the period of exposure of microbes to the drug. The bacteriostatic concentration with a brief period of exposure (6 h) was lower than the conventional MIC for Escherichia coli and Klebsiella sp. When the period of exposure was prolonged (18–42 h), the bacteriostatic concentration almost corresponded with the MIC. In contrast to these gram-negatives, the bacteriostatic concentration with a brief period of exposure roughly corresponded with the MIC for strains of Staphylococcus aureus and was higher for enterococcus. When a comparison of the bacteriostatic and the bactericidal concentrations was used as the criterion for assessment, the mode of action of cephalothin appeared to be bactericidal to most of the gram-negatives. This drug was bacteriostatic to a number of strains of gram-positives, in particular to enterococcus, especially when microbes were exposed to the drag over a brief period of time.