Effect of some psychotropic drugs and a barbiturate on mycoplasmas.

The inhibitory effect of selected membrane stabilisers on Mycoplasma pneumoniae, M. hominis and Ureaplasma urealyticum was investigated in vitro. The phenothiazine chlorpromazine (CPZ) and the barbiturate thiopental (Leopental(R)) as well as the stereo-isomeric thioxanthene derivatives; cis(Z)-clopenthixol (Zu-clopenthixol(R))/ trans (E)-clopenthixol and cis (Z)-chlorprothixen (Truxal(R))/trans(E)-chlorprothixen, all have antimycoplasmal effect in the range 3.9-312 mg/l, measured as growth inhibition. It was also demonstrated that the enzymatic functions of the different mycoplasma strains, such as breakdown of glucose, arginine and urea, were abolished by concentrations of CPZ that were sufficiently low to allow multiplication of the organisms. A similar effect was obtained with Leopental(R) although the mycoplasmas were generally only half as sensitive to this drug. Also M. gallisepticum and Acholeplasma laidlawii were inhibited by CPZ and Thiopental. The four thioxanthenes were all inhibitory to mycoplasmal growth and the effect was independent of their stereo-isomeric configuration. The clopenthixol stereoisomers, but not the chlorprothixene isomers, inhibited colour change at concentrations lower than those which inhibited growth. While enzyme activity may continue for some time in vitro when classic antibiotics have inhibited mycoplasmal growth, the reverse effect was observed with phenothiazines and thioxanthenes. The membrane stabilisers may be useful tools in the investigation of microbiological activity on the mycoplasma membrane. From these drugs, new 'antibiotics' might be developed with another action than that of the known antimycoplasmal drugs.