Effect of chlorpromazine on conjugal plasmid transfer and sex pili.

The major tranquillizer chlorpromazine (Cpz) inhibited the conjugal transfer of R and F'lac plasmids. The frequency of transfer of R-144 and R-100 plasmids was reduced with 2-3 log by Cpz at a concentration of 50-100 microgram/ml, while the frequency of RM-98 plasmid did not change under the same conditions. Cpz at 100 microgram/ml was an effective inhibitor of the transfer of F'lac plasmid. By means of electron microscopy and plaque assay, 100 microgram/ml Cpz was shown to reduce the adsorption rate of male specific ribonucleic acid phages MS-2 to the sides of F-pili. Common pili and flagellae seemed to be intact, but sex pili probably retracted in the presence of Cpz.