Abstract
Summary and conclusions
The resistance of a strain of Klebsiella pneumoniae to chloramphenicol was enhanced 128-fold by serial subculture on the surface of agar plates containing graded concentrations of this antibiotic.
A chloramphenicol-dependent variant also emerged during the course of these subcultures. This variant grew best in the presence of a critical concentration of chloramphenicol; as the concentration of antibiotic was either increased progressively beyond this critical level or decreased below it there was a steady decline in growth until complete inhibition of growth occurred.
The chloramphenicol-dependent variant was first recognized soon after the resistance of the strain had been enhanced to a point where it was completely inhibited by this critical concentration.
Evidence was also obtained of possible “back-mutation” to variants which were as sensitive as the parent strain.
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