A Method for Detection of Streptothricin in the Presence of Streptomycin

Streptomycin 1 and streptothricin, 2 two antibiotic agents having almost identical bacterial spectra, 3 , 4 are both produced by members of the actinomycetes, namely, Actinomyces griseus and Actinomyces lavendulae respectively. Because of this close relationship and of the still existing difficulty in the identification of the various members of the actinomycetes, 5 it is possible that strains of the organisms producing these 2 antibiotics might be confused. Such a confusion would be particularly undesirable when it is recognized that streptothricin is many times more toxic than streptomycin and in addition, has a distinct delayed toxicity. 6 , 7 Streptomycin, on the other hand, because of its relative non-toxicity and its active inhibition of gram-negative bacteria both in vitro and in vivo 3 , 8 has aroused a considerable amount of interest in the medical field. Realizing the difficulties which would be encountered if samples of streptomycin were to become contaminated with the more toxic streptothricin, it was considered essential that there be developed a means of detecting small amounts of streptothricin in the presence of large quantities of streptomycin. A method for differentiating between streptomycin and streptothricin has been announced recently. 9 However, a more simplified microbiological test has been devised which can detect as little as 0.1% of streptothricin present as a contaminant in streptomycin. The procedure is based upon a modification of the Stebbins and Robinson. 10 cup-assay for streptomycin. The organism used in the test is a strain of an unidentified gram-negative rod∗ which as found to be every resistant to streptomycin, but sensitive to streptothricin when tested for sensitivity by means of the agar-streak method.