Mutations isolated from the two synonymous versions of the gene aac(6��)-Ib.

1Gene mutant libraries were independently screened for enhanced resistance phenotype on six different aminoglycoside antibiotics. Each aa substitution is directed by a single nucleotide difference. Three out of five substitutions (L102S, S83N and L55Q) are directly accessible by only one of the gene version, and were not isolated from any library of the alternative gene.2The number of independent colonies carrying the mutation isolates from the corresponding libraries.3The global improvement of resistance phenotype is measured by the Minimum Inhibitory Concentration (MIC). To avoid any influence of the sequence background on observed phenotypes, mutations isolated from aacELP were reconstructed by site directed mutagenesis and tested in aacWT.4No mutant was selected on the aminoglycosides kanamycin, neomycin and tobramycin, nor on the fluoroquinolones ciprofloxacin, levofloxacin and ofloxacin.5The L102S mutation corresponds to the L83S mutation described by Lambert and col. The numbering difference is due to an error in the start codon choice in their original characterization [16].6ND: Not Detected.