Abstract
Aside from penicillin, streptothricin is the only antibiotic whose pharmacologic properties indicate a suitability for general use in the animal organism. 1 , 2 Interest in the development of an antituberculosis agent of microbiological origin led to in vitro tests of the efficacy of the only 2 antibiotics known which at present could possibly be of general use in animals or humans, namely, penicillin and streptothricin.
Various species of mycobacteria were totally resistant to the action of penicillin, even as much as 1,000 Oxford units per ml. Further studies revealed that this resistance probably is due to the abundant formation of a penicillin-destroying enzyme, presumably penicillinase. Details of this are reported elsewhere. 3
A study of the inhibitory action of streptothricin for 5 Mycobacterium cultures is included in Table I. Since streptothricin is stable, a single addition of the antibiotic was sufficient to maintain the desired unitage over the period of 6 to 8 weeks necessary for growth of some strains of mycobacteria. Streptothricin was particularly effective in Long's medium; this is probably the result of the alkalinity of the medium which is known to enhance the in vitro activity of streptothricin. 4 The inhibitory range of 0.1 to 1.0 unit of streptothricin per ml places these Mycobacterium cultures among the most sensitive organisms to streptothricin. M. phlei previously was found sensitive. 5
A rough indication was obtained for the bactericidal action of streptothricin upon mycobacteria. Long's medium containing various quantities of streptothricin was inoculated heavily with 4 Mycobacterium strains. After 14 days' inhibition, portions of each culture were streaked on Long's agar to determine viability of the cells in the inoculum. Table II indicates that streptothricin was definitely bactericidal in low concentrations.
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