DNA probes for studying streptothricin resistance evolution in enteric bacteria

Probes for the detection of streptothricin resistance genes have been derived from recombinant plasmids. These include the streptothricin resistance gene probe sat 1/2 derived from Tn 1826 and specific for both the sat-1 determinant of Tn 1825 and the sat-2 determinant of Tn 1826, and the probe sat D derived from and specific for the sat-1 determinant of transposon Tn 1825. A third streptothricin resistance gene probe, sat 3, represents the streptothricin resistance determinant sat-3 of the IncQ R plasmid pIE639. Hybridization studies did not reveal any sequence homology between sat-3 and the transposon-localized sat-1 and sat-2 determinants. Moreover, non of the different sat-determinants isolated from plasmids of gram negative bacteria hybridized with the analogous resistance determinant of Streptomyces noursei, which had been cloned and named nat by Krügel et al. (Gene, 1988, 62, 209-214). The sat 1/2 probe in combination with the sat D probe proved to be suitable for the identification and the differentiation of sat-1 and sat-2 determinants in different genetic environments. Streptothricin resistance genes related to those present on transposons Tn 1825 and Tn 1826 have been detected by hybridization with the probe sat 1/2 on plasmids isolated a long time ago before the application of streptothricins. The sat-3 determinant appears to be exclusively associated with the IncQ plasmid pIE639.