In vitro susceptibility testing of Paracoccidioides brasiliensis to sulfonamides

A total of 60 clinical isolates of Paracoccidioides brasiliensis were tested for susceptibility to sulfadiazine and sulfadimethoxyne by the agar dilution technique. A modification of the Mueller-Hinton medium was devised which gave good growth of the yeast form. The minimum inhibitory concentrations for only 51.6% of the isolates were in the range of the recommended blood serum concentration (50 micrograms/ml). For 6 to 8% of the isolates, the minimum inhibitory concentrations were above 200 micrograms of both sulfadiazine and sulfadimethoxyne per ml. A significant decreases in susceptibility was demonstrated for one isolate obtained from a patient relapsing during sulfonamide therapy.