FIG. 3.

Detection of chloramphenicol secreted into the growth medium of S. venezuelae cultures. A 1.5-ml aliquot of supernatant from cultures of wild-type S. venezuelae was extracted with ethyl acetate and transferred to a filter paper disk. Top agar supplemented with AB7341λφ[cspA::lacZ] cells was poured over an LB agar plate spread with X-Gal, and the disk was placed on the surface. The plate was incubated overnight at 37°C. The disk contained ∼7.5 μg of chloramphenicol, as estimated by TLC.