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Infect Immun. 1971 April; 3(4): 530-534
Copyright © 1971 American Society for Microbiology. All Rights Reserved.

Mechanism of Action of Isoniazid on Mycobacterium bovis Strain BCG

Department of Clinical Laboratories, National Jewish Hospital and Research Center, Denver, Colorado 80206

ABSTRACT

The mechanism of action of isoniazid (INH) on Mycobacterium bovis strain BCG was studied. The rates of synthesis of deoxyribonucleic acid (DNA), ribonucleic acid (RNA), and protein after the addition of INH to growing cultures were followed by measuring the incorporation of ³H-thymidine, ³H-uridine, and ¹⁴C-L-valine, respectively. After the addition of INH, the rate of DNA synthesis began to decrease and was abolished within 4 hr. RNA synthesis ceased after 6 hr, and protein synthesis was inhibited after 7 hr. Thus, it appears that inhibition of the synthesis of DNA is one of the earliest events after INH addition. The inhibition of the synthesis of DNA was further found to correspond to losses in viability of treated cultures. Degradation of preexisting DNA in INH-treated strain BCG was not detected.