Antimicrobial activity of phenothiazines, benzo[a]phenothiazines and benz[c]acridines

The abilities of 14 phenothiazines, 8 benzo[a]phenothiazines and 12 benz[c]acridines to induce an antibacterial effect against Escherichia coli K12 were compared. Several phenothiazines, which showed antiplasmid activity, displayed the most potent antibacterial activity. All benz[c]acridine derivatives were moderately antibacterial, whereas benzo[a]phenothiazines were inactive. The active phenothiazine derivatives had more potent inhibitory activity against fungi, including phytopathogen filamentous, human pathogen filamentous fungi and yeasts, than against gram-positive and -negative bacteria. Taken together with previously reported data, the induction mechanism of antimicrobial and antiplasmid activity by these compounds seems to be different from that of antitumor, differentiation-inducing and carcinogenic activity.