FIG. 1.

Paradoxical survival in the presence of chloramphenicol. An exponentially growing culture of strain KD2140 (gyrA67 gyrB225) was treated with 20 μg/ml chloramphenicol for 10 min prior to addition of the indicated concentrations of nalidixic acid for an additional 180 min, at which time samples were diluted, applied to drug-free agar, and incubated to determine bacterial survival. Symbols: filled circles, cultures with chloramphenicol; open circles, cultures without chloramphenicol. Similar results were obtained in a replicate experiment.