Mode of action of ethambutol

Forbes, M. (Lederle Laboratories Division, Pearl River, N.Y.), N. A. Kuck, and E. A. Peets. Mode of action of ethambutol. J. Bacteriol. 84:1099-1103. 1962.-Ethambutol [2,2'-(ethylenediimino) di-1-butanol] arrested multiplication of Mycobacterium smegmatis cells and eventually effected their death. The inhibitory effect of the drug on multiplication did not become apparent until several hours after its addition to the culture. The drug had no effect on the survival of nonproliferating cells. It had little or no effect on the metabolism of nonproliferating cells, but cells from cultures whose growth had been inhibited by ethambutol showed evidence of impaired metabolism. C(14)-labeled ethambutol was taken up rapidly by both proliferating and nonproliferating cells. The observations are consistent with the hypothesis that ethambutol exerts its antibacterial effect by interfering with the synthesis of a metabolite(s) needed for multiplication. Depletion of the metabolite(s) results in arrest of multiplication, impairment of metabolism, and loss of viability. Resistance to ethambutol cannot be explained by the failure of the cells to take up the drug, since the drug was equally bound by resistant and sensitive cells.

EFFECT OF ETHAMBUTOL ON NUCLEIC ACID METABOLISM IN MYCOBACTERIUM SMEGMATIS AND ITS REVERSAL BY POLYAMINES AND DIVALENT CATIONS

Forbes, M. (Lederle Laboratories Division, Pearl River, N.Y.), N. A. Kuck, and E. A. Peets. Effect of ethambutol on nucleic acid metabolism in Mycobacterium smegmatis and its reversal by polyamines and divalent cations. J. Bacteriol. 89:1299-1305. 1965.-Mycobacterium smegmatis, harvested from cultures inhibited by ethambutol and then suspended in drug-free medium, exhibited a prolonged lag before growth resumed. Polyamines and magnesium ions shortened this lag. Polyamines and magnesium added to the culture increased the minimal inhibitory concentration of the drug and reversed the inhibitory effect of the drug, even when added after the drug had already inhibited growth. When ethambutol was added to a culture in its exponential phase of growth, synthesis of protein and deoxyribonucleic acid (DNA), as measured by incorporation of S(35) and P(32), continued for 3 hr at a rate slightly less than in the control cells and then essentially ceased. Synthesis of ribonucleic acid (RNA) was depressed, but it proceeded even after protein synthesis had ceased. Even though the synthesis of RNA continued, the net RNA decreased, and inhibited cells became deficient in RNA. Polyamines and divalent cations, which reverse the inhibitory effect of the drug, have been reported to be involved in nucleic acid turnover. These considerations suggested that ethambutol may exert its inhibitory effect by interfering with a function of cellular polyamines and divalent cations in RNA metabolism.

EFFECT OF ETHAMBUTOL ON CYTOLOGY OF MYCOBACTERIUM SMEGMATIS

Gale, Glen R. (Veterans Administration Hospital, Durham, N.C.) and Helen H. McLain. Effect of ethambutol on cytology of Mycobacterium smegmatis. J. Bacteriol. 86:749-756. 1963.-Electron microscopy showed the effects of the antimycobacterial drug, ethambutol [d-2,2'-(ethylenediimino)-di-1-butanol], on the cytology of Mycobacterium smegmatis. After 10 hr of exposure to the drug, cells no longer contained material which, in control cells, was closely associated with cellular division, possibly genetic substance. No marked changes were observed in other cellular structures. It was concluded that the drug may block one or more steps in the synthesis of pentose nucleic acid or deoxypentose nucleic acid, ultimately causing cessation of cellular division and loss of viability. These cytological findings were compatible with results of other investigators on the mode of action of this drug.

THE TREATMENT OF BONE AND JOINT TUBERCULOSIS

Images