Published online by Cambridge University Press: 14 April 2009
Chloramphenicol (CM), Aureomycin (AM) and Puromycin (PM) induce RNA synthesis in RC-stringent Escherichia coli starved of a required amino acid. This fact has been used to develop a method for comparing the levels of resistance of single-step CM-r mutants to the three antibiotics. Three levels of resistance to each antibiotic were found among four mutants selected in a single CM-s strain. The mutant with the highest CM resistance has the lowest AM resistance, and vice versa, while the level of PM resistance was not correlated with that of either CM or AM. The four mutants all differed from each other in their patterns of resistance to the three antibiotics.