TABLE 1.

Level of tetracycline resistancea is determined by a combination of background genotype and 16S rDNA allele

Recipient strainTetracycline concn (μg/ml) allowing growth of strainb:
WT (AGA965-967)Lit76 (gtA965-967)Aus108 (ttc965-967)
Ind751.5832
WT 266950.5816
Tetr 26695 (non-rDNA)61664
  • a Tetracycline resistance levels were difficult to define with precision, because increases in tetracycline levels resulted in progressive decreases in colony size and efficiency of colony formation, as detailed in Materials and Methods.

  • b The tetracycline concentration that still allowed pretty good growth. The levels tested by efficiency-of-plating assays were 0 0.5, 1.5 or 2, 4, 6, 8, 12, 16, 32, 64 and 128 μg of tetracycline per ml. The resistance levels given here are the highest levels that cause no more than a 10-fold decrease in efficiency of colony formation relative to that caused by the next highest level of tetracycline, as detailed in Materials and Methods. WT, wild type.