The Contribution of a Novel Ribosomal S12 Mutation to Aminoglycoside Resistance ofEscherichia coliMutants

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Abstract
This study characterised the contribution of a novel ribosomal S12 mutation to aminoglycoside resistance in Escherichia coli via step-wise mutation analysis. Mutants of E. coli NCTC 10418 were selected in four separate progressive series (I-IV) on plates containing increasing aminoglycoside (streptomycin, neomycin, gentamicin, tobramycin, and kanamycin) concentrations. Minimum inhibitory concentrations (MICs) of these aminoglycosides were established for the most resistant mutants in each series. There was no cross-resistance between streptomycin and the other aminoglycosides tested; however there was cross-resistance between the neomycin, tobramycin and kanamycin resistant mutants. DNA sequencing of a 423bp region of the rpsL gene encoding S12 revealed a novel Lys87-->Glu mutation in the streptomycin selected resistant mutants, while there were no S12 mutations in resistant mutants resulting from selection with neomycin, gentamicin, and tobramycin and kanamycin.