Abstract
The effect of thallium acetate on the growth of Proteus mirabilis (strain 9) and its L-phase variant (strain L9) was investigated. In the fluid medium, thallium acetate at a concentration of 1:4000 did not affect the maximum growth titre and the growth rate of these organisms. At a concentration of 1:2000, their maximum growth titre was reduced by 1 in 10 in comparison with that at a concentration of 1:4000, and the growth rate of strain 9 was delayed considerably although that of strain L9 was not affected. On the agar medium, strain L9 was inhibited slightly at 1:4000 concentration of thallium acetate while strain 9 was not, but it was inhibited at a concentration of l:2000. Production of exceedingly small colonies of strain 9 and inhibition of swarming were observed on an agar culture containing thallium acetate but the size of the colonies became larger gradually with the length of the incubation period. Based on the results obtained in the present study, it may be concluded that in general the attitude of Proteus mirabilis and its L phase variant toward thallium acetate is almost similar.
