Observations on Bacteriostatic and Bactericidal Action of Erythromycin. ∗

Summary

1. Erythromycin was bactericidal to low cell concentrations of growing S. aureus but not to heavy suspensions of the same growing cells. 2. Turbidity of the heavy suspension continued to increase after addition of erythromycin, although at a reduced rate. This increase was not paralleled by any increase in viable units. 3. Viable cells in a drug-treated suspension were still as sensitive to erythromycin as before addition of the drug. 4. Addition of a nitrate of a drug-treated, dense suspension to a dilute suspension of growing cells delayed onset and reduced rate of sterilization of these cells by erythromycin.