FIG 3.

Effect of heme on the growth of metronidazole-resistant and -susceptible C. difficile in brain heart infusion (BHI) broth in the presence and absence of metronidazole. (A and B) Metronidazole-resistant 7/34 and IT1001 only grew in metronidazole (4 μg/ml) when heme was added. (C and D) Heme did not rescue the inhibition of metronidazole-susceptible CD196 and ATCC 43596. In the absence of drug, heme did not enhance the growth of the tested strains. Growth curves are plotted as the means from three biological replicates with standard errors of the means; error bars for CD196 and IT1001 are not seen, as they are shorter than the size of the symbol in their plots.