Resistance to streptothricin was studied in bacteria with diffcrent resistance mechanisms. Thc laboratory-induced streptothricin-resistant mutant E. coli A19 Stcr 2/2/1 showed a high level of cross-resistance to aminoglycosides and other miscoding inducing antibiotics. In contrast, aminoglycosid-resistant E. coli strains with plasmid-determined aminoglycoside modifying enzymes were sensitive to streptothricin. Enzymatic inactivation of streptothricin by acetylation was demonstrated for the streptothricin producing Streptomyces noursei, strain NG13. This strain showed no cross-resistance t o miscoding inducing aminoglycosides.
Recent investigations of the mode of action of streptothricin F in cell free protein synthesis have shown that streptothricin inhibits primarily the step of translocation and, in addition, induces miscoding (HAUPT et al. 1978 and 1980). These effects of streptothricin resemble those of aminoglycoside antibiotics such as neomycin and kanamycin. With regard to its use in animal nutrition and plant protection, resistance to streptothricin and cross-resistance between streptothricin and aminoglycoside antibiotics are of special interest. I n the present paper, we report on the cross-resistance between streptothricin and aminoglycoside antibiotics, using bacteria with various resistance mechanisms.