Effect of cephalothin on growth patterns of micro-organisms

Isolates of Staphylococcus aureus, Escherichia coli. Klebsiella pneumoniae and Proteus mirabilis were incubated in the presence of inhibitory concentrations of cephalothin. After destruction of the antibiotic, there was a lag phase before S. aureus began to proliferate again. When similar experiments were conducted with E. coli, K. pneumoniae, and P. mirabilis, no lag phase was observed. This data suggests that the inhibitory activity of cephalosporins may be different for gram-positive cocci and gram-negative bacilli.