FIG 3.

Heteroresistance phenotype toward Staphylococcus aureus can be induced by hemin. (a) In a double disk diffusion using trimethoprim-sulfamethoxazole- and hemin-impregnated disks, there was a distortion of the inhibition zone due to growth within the inhibition zone of the SXT-heteroresistant isolate D2198 on standard Mueller-Hinton agar (left panel), which was also visible in the Etest (right panel). (b) The growth characteristics of SXT-susceptible ATCC 25923 was not affected by hemin. The variations in the color of the hemin disk may be the result of uneven distribution/diffusion into the agar medium or hemin saturation in the area surrounding the disks.