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Now let’s take a different
point of view and see whether there are existing compounds that have a very narrow
selection window. To get at this we measured both MIC and MPC. Then we determined the
ratio of MPC to MIC (a ratio of 1 would mean that the window is closed). As you can see,
no compound tested has a value of 1. Indeed, some compounds, such as rifampicin, have such
wide selection windows that no drug concentration will block mutant growth. This is the
result you would expect to see with a population of bacteria that contained a small
subpopulation of plasmid-containing cells that are highly resistant. For such situations
multidrug therapy is needed to close the selection window. |