Microcalorimetric investigation of the action of cinoxacin against Escherichia coli

Abstract

The heat effects produced by a culture of E. coli exposed to cinoxacin were registered by a flow microcalorimeter of the heat conduction type. The drug decreased and delayed the heat effects. There was a late, second increase in the heat effects, which was due to selection of cinoxacin-resistant mutants. The organisms used had a MIC of 1.7 μg/ml, whereas the organisms recovered after approximately 17 h exposure to cinoxacin had a MIC of 400 μg/ml. Formation of highly elongated bacterial cells occurred within an hour after the introduction of the drug. After 5 h, lysis of the elongated cells was found. There was a correlation between the heat effects evolved and the number of colony forming units/ml.