RESISTANCE PATTERN OF MYCOBACTERIUM TUBERCULOSIS (H₃₇Rv) TO A NEW ANTIBIOTIC, LIVIDOMYCIN

Abstract

The resistance pattern of Mycobacterium tuberculosis strain H₃₇Rv to a new antibiotic lividomycin was studied using a technique previously described. The results obtained are shown in Fig. and Table.
Mycobacterium tuberculosis strain H₃₇Rv showed only one phenotype of resistance, which is shown as a survival curve in figure, and the upper limit of resistance was a 400μEg/ml level. Repeated selection by the drug was ineffective to obtain a more resistant strain. The organism was either resistant to 25μg/ml of the drug, as was the parent strain not exposed previously to the drug, or resistant to 400μg/ml of the drug. The resistance pattern was shown to be a single-step pattern.
Resistant mutants, which give rise to resistant strains capable of growing on the 400μg/ml level of the drug, were obtained at a rate of 2×10^-6 among the organisms of the parent strain.
The most striking finding was that the resistant mutants are very dysgonic at primary isolation and the colonies of the resistant mutants could be detected only after incubation at 37°C for 8 weeks. The strains could grow showing a normal growth rate at the second and successive transers.