Resistance mutations investigated and corresponding resistance phenotype

Type of rRNA mutationNo. of spontaneous mutants obtained by selective plating/total no. of isolates testedbResistance phenotypeMICc (μg/ml)Resistance mutation observed in clinical pathogensd
16S rRNA 522 C→T2/22Streptomycin250+
16S rRNA 523 A→Ca1/22Streptomycin125+
16S rRNA 524 G→Ca12/22Streptomycin>500
16S rRNA 526 C→Ta7/22Streptomycin125+
16S rRNA 1408 A→Ga10/102-Deoxystreptamines>500e+
23S rRNA2058 A→Ga7/8Macrolides, lincosamides, streptogramin B128f+
23S rRNA 2059 A→Ga1/8Macrolides, streptogramin B128f+
  • a The indicated mutations were also introduced into M. smegmatis by recombinant DNA techniques.

  • b A total of 40 independent laboratory mutants were obtained in vitro, 22 were resistant to streptomycin, 10 were resistant to 2-deoxystreptamines, and 8 were resistant to macrolides.

  • c The MICs of drug-susceptible M. smegmatis strains are as follows: streptomycin, 1.0 μg/ml; amikacin, 0.6 μg/ml; clarithromycin, 0.06 μg/ml.

  • d Tabulated from previous reports (10, 11, 16, 22, 23, 24, 29, 31, 33, 40, 41).

  • e Amikacin was chosen as a representative of the 2-deoxystreptamines.

  • f Clarithromycin was chosen as a representative of the macrolides.