Antibacterial effect of some phenothiazine compounds and R-factor elimination by chlorpromazine

Chlorpromazine, levopromazine and promethazine exerted a bacteriostatic effect on Gram-positive bacteria at 20-60 mug/ml, on Gram-negative bacteria at 130-180 mug/ml concentration. Of the three compounds, chlorpromazine had the most marked bactericidal effect on cultures of Bacillus anthracis growing in minimal medium. In addition, chlorpromazine had a significant bactericidal effect on the resting cells of Escherichia coli suspended in saline. Pseudomonas aeruginosa was resistant to phenothiazines. Experiments have failed to derive resistant mutants from the highly sensitive B. anthracis. An effective R-factor elimination was observed at chlorpromazine concentrations of 50 mug/ml, practically not affecting the growth of multiple resistant E. coli.