A conspicuous adaptability to antibiotics in theEscherichia colimutator strain,dnaQ49

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Abstract
By repeating the cycle of mutagenesis and selection, the Escherichia coli dnaQ49 mutator acquired high level resistance to ampicillin (30 000 µg ml−1), streptomycin (26 000 µg ml−1) and ofloxacin (3000 µg ml−1). Under the strong pressure of ofloxacin, dnaQ49 also followed the history of mutations in the gyrase and topoisomerase IV genes previously observed in clinical isolates of quinolone-resistant E. coli. The results of these in vitro experiments suggest that naturally existing mutators may participate in the rapid acquisition of resistance to various antibiotics in patients. A possible mechanism for the occurrence of this adaptability is discussed with special reference to the property of mutagenesis accompanying DNA replication.
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