Since blocking growth is different from killing cells, we needed to also compare the compounds for lethal activity. This was done by treating a liquid culture of cells with one compound or the other, and then the cells were plated on drug-free agar to determine the number of survivors. As shown in panel A, the methoxy compound is a little bit better than the C-8-H derivative with wild-type cells (8). The difference with the gyrA mutant is striking (panel B). Similar results were obtained with E. coli (21).