Comparison of the contamination rates of culture media used for isolation and identification of dermatophytes

Abstract

Mycological media that promote spore production are essential for the diagnosis of dermatophytosis. However, these culture media frequently become contaminated by multiple fungal or bacterial species during culture. The aim of this study was to compare the contamination rates of 6 culture media used for the isolation and identification of dermatophytes, including Borelli's lactritmel agar (BLA), brain-heart infusion agar (BHIA), Lowenstein-Jensen agar (LJA), malt extract agar (MEA), potato dextrose agar (PDA), and Sabouraud glucose agar (SGA). Agar plates were inoculated with 43 well-characterized dermatophyte strains, belonging to the genera Arthroderma, Epidermophyton, Microsporum, or Trichophyton. The agar plates were incubated at 26 °C and examined every 5 days for 1 month. By the end of the incubation period, 97 of the 258 plates (37.6%) were contaminated by fungi. No bacteria were detected. Overall, BLA demonstrated the lowest rate of contamination, followed by SGA, MEA, BHIA, PDA, and LJA. Sequencing of the internal transcribed spacer region rDNA of the contaminant fungi revealed that Aspergillus and Penicillium species were the most common contaminants. These results suggest that nonenriched culture media types, such as BLA or SGA, reduced contamination during dermatophyte subculture.