A COMBINATION OF sbmA AND tolC MUTATIONS IN Escherichia coli K-12 Tn10–CARRYING STRAINS RESULTS IN HYPERSUSCEPTIBILITY TO TETRACYCLINE

Departamento de Bioquímica de la Nutrición, Instituto Superior de Investigaciones Biológicas (Consejo Nacional de Investigaciones Científicas y Técnicas-Universidad Nacional de Tucumán) and Instituto de Química Biológica "Dr Bernabé Bloj", Chacabuco 461, 4000 San Miguel de Tucumán, Tucumán, Argentina

^* To whom correspondence should be addressed. Email: salomon{at}fbqf.unt.edu.ar.

	Abstract

Previously, we demonstrated that Escherichia coli tolC mutations reduce the high-level resistance to tetracycline afforded by transposon Tn10-encoded TetA pump from 200 µg/ml to 40 µg/ml. Here, we have found that the addition of a sbmA mutation to a tolC::Tn10 mutant exacerbates this phenotype: the double mutant does not form colonies even in the presence of as low a concentration of tetracycline as 5 µg/ml. Inactivation of sbmA alone partially inhibited high-level tetracycline resistance, from 200 to 120 µg/ml. It thus appears to exist an additive effect of the mutations, resulting in almost complete suppression of the phenotypic expression of Tn10 tetracycline resistance.