The environmental source of emerging Apophysomyces variabilis infection in India

The rare mucoraceous fungus, Apophysomyces species complex ranks second after Rhizopus arrhizus causing mucormycosis in India. The source of this agent in the environment is not clearly known. We conducted an environmental study to find its presence in Indian soil. The soil samples from different geographical locations were analyzed for isolation of Mucorales. Rhizopus arrhizus (24.6%) was most commonly isolated from soil, followed by Lichtheimia spp. (23.2%), Cunninghamella spp. (21.7%), Rhizopus microsporus (14%) and Apophysomyces spp. (4.5%). The isolation of Apophysomyces species complex was significantly associated with low nitrogen content of the soil. Based on sequencing of internal transcribed spacer (ITS) and 28S (D1/D2) regions of ribosomal DNA, the Apophysomyces isolates were identified as Apophysomyces variabilis with 98 to 100% similarity to type strain A. variabilis (CBS658.93). The analysis of amplified fragment length polymorphism (AFLP) fingerprinting data demonstrated genomic diversity of A. variabilis isolates with multiple clades (similarity 40-90%). The minimum inhibitory concentrations (MIC), MIC50 and MIC90 for A. variabilis isolates were 1 and 4 μg/ml for amphotericin B, 0.25 and 0.5 μg/ml for itraconazole, 0.125 and 0.25 μg/ml for posaconazole, 0.06 and 0.12 μg/ml for terbinafine, respectively. The present study revealed abundant presence of A. variabilis in Indian soil with low nitrogen content, its genetic heterogeneity and relatively high MICs for amphotericin B.