XI International Meeting on Paracoccidioidomycosis

XI International Meeting on Paracoccidioidomycosis

Resume:113-1

Poster (Painel)

113-1	Subpopulations of the pathogenic fungus Paracoccidioides brasiliensis potentially resistant to sulfamethoxazole and an atypical clone showing a blockage on the dimorphic transition
Authors:	Rosana de Carvalho Cruz (UFMG - Universidade Federal de Minas Gerais) ; Carolina Santos Oliveira (UFMG - Universidade Federal de Minas Gerais) ; Silvia Maria Cordeiro Werneck (UFMG - Universidade Federal de Minas Gerais) ; Patricia Silva Cisalpino (UFMG - Universidade Federal de Minas Gerais)

Abstract

Paracoccidioides brasiliensis, a dimorphic fungus, is usually sensitive in vitro to the antifungal agents used in therapy. However, evidences of resistance to sulfonamide have been registered. The objective of the present work was to select subpopulations of P. brasiliensis tolerant to increasing concentrations of sulfamethoxazole. The minimum inhibitory concentrations (MIC) of antifungals to 21 clinical and environmental isolates were determined. Six fungal isolates (A, B, C, D, E and F), including representatives from distinct phylogenetic species (S1, PS2 and "Pb01-like"), with MIC values of 300 μg/mL for sulfamethoxazole were chosen to start selection procedures. Using Single Step technique, each inoculum was plated on YPD agar with 300 and 400 μg/mL of sulfamethoxazole at 37ºC for 20-30 days. Colonies were selected and submitted to three raises of antifungal concentration challenging to 400, 500, 600 and 700 μg/mL of the drug. There were obtained 45 colonies of the isolate D at 400 μg/mL and 10 at 500 μg/mL, 39 of isolate E at 400 μg/mL and 12 at 500 μg/mL, 47 of isolate B at 400 μg/mL, 14 of isolate A at 300 μg/mL and 40 colonies of isolate C at 400 μg/mL. No subpopulations of isolate F were selected. After the 10th subculture, two clones of the isolates A and D, and one of the isolate B grew to 700 μg/mL of sulfamethoxazole, two clones of the isolate C and one of isolate E grew at 600 μg / mL. These isolates were considered potentially resistant once subpopulations with MIC above 300 μg/mL could be so characterized. The resistance phenotype was stable after successive subcultures in the absence of the antifungal agent. Colonies from a seventh and distinct isolate (G), representative of the phylogenetic species S1, were also selected at the room temperature in the presence of 300 μg/mL of sulfamethoxazole. After subsequent challenge with increasing drug concentrations, three clones grew at 400 μg/mL, all revealing an atypical cerebriform morphology and yeast phenotype at room temperature, being stable after successive subcultures in the absence of the antifungal agent, independent of the presence of the drug. This is the first report on the isolation of P. brasiliensis resistant to sulfamethoxazole besides showing a blockage on dimorphic transition, potentially interesting to study this biological process. ਀匀甀瀀瀀漀爀琀攀搀戀礀䌀一倀焀愀渀搀䘀愀瀀攀洀椀最

Keyword: dimorphism, Paracoccidioides brasiliensis, selection, sulfamethoxazole

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