Specific inhibition of spermidine synthesis in Mycobacteria spp. by the dextro isomer of ethambutol

Only the dextro isomer of ethambutol inhibited mycobacterial spermidine synthase and spermidine biosynthesis. Inhibition of mycobacterial spermidine synthase appeared to be specific. Spermidine synthase from Mycobacterium fortuitum, which was resistant to ethambutol in vitro, required a higher concentration of ethambutol for its inhibition than the enzyme of susceptible Mycobacterium bovis.