Effect of growth phase on the bactericidal action of chloramphenicol against Haemophilus infuenzae type b and Escherichia coli K-1

The bactericidal action of chloramphenicol against six H. influenzae type b isolates and six E. coli K-1 isolates was compared. Quantitative kinetic studies indicated that each chloramphenicol concentration killed H. influenzae cells in the stationary phase of growth significantly more rapidly than it did those in the exponential phase of growth. E. coli in either the stationary or the exponential phase were killed at the same rate by 80 mu g of chloramphenicol per ml. The results suggest that chloramphenicol may kill these organisms by different mechanisms.