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Sensitivity of Escherichia coli to Atabrine Conferred by R Factor and Its Potential Clinical Significance

^a Department of Microbiology, School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania

ABSTRACT

A comparative study of the inhibitory effect of Atabrine on R^– and R⁺ strains of Escherichia coli showed that R⁺ cells were killed when grown in the presence of Atabrine, whereas R^– cells were not. It would appear, therefore, that R factor confers sensitivity to Atabrine on the host cells. The "curing" of R factor from R⁺ cells by the ultraviolet light-acridine orange method rendered the "cured" cells more resistant than even the parent R^– cells. The "cured" cells reinfected by R factor were more sensitive than the "cured" cells but less sensitive than the original R⁺ cells. After growth once in Atabrine, and even after subcultures in drug-free medium, the growth of R⁺ cells in the presence of Atabrine was more rapid than that of the R^– cells. R^– cells made resistant by growing them repeatedly in streptomycin, chloramphenicol, tetracycline, and sulfathiazole in succession also showed a higher degree of sensitivity to Atabrine than the original R^– cells. When mixtures of R^– and R⁺ cells were grown in 120 µg/ml of Atabrine, R⁺ cells were killed and the culture consisted predominantly of R^– cells. A mixture of R^– and R⁺ cells (1:10,000) inoculated into the Atabrine-containing medium and treated 24 hr later with chloramphenicol was completely killed.

¹ On leave of absence from Department of Microbiology, School of Medicine, University of Tokyo, Tokyo, Japan.