Identification of subtilisin genes as a potential virulence factor in Trichophyton mentagrophytes isolated from human and bovine dermatophytosis lesions in Iran

Dermatophytes are responsible for the majority of human and animal cutaneous mycoses. Proteases secreted by dermatophytes offer potential virulence factors. Multiple proteases have been discovered as possible virulence factors. In Iran, however, no human nor animal isolates of Trichophyton mentagrophytes have been examined for the presence of the subtilisin (SUB) gene family. Therefore, we investigated the existence of SUB1-7 genes in T. mentagrophytes isolated from dermatophytosis lesions in humans and animals. Ten and eight molecularly verified T. mentagrophytes isolates obtained from human and bovine dermatophytosis, respectively, were examined for the presence of SUB genes. In two multiplex PCR panels, all T. mentagrophytes strains were examined. The initial multiplex PCR primers detected the presence of SUB1, SUB4, SUB5, and SUB6. The second multiplex PCR panel includes SUB2, SUB3, and SUB7 specific primers. DNA sequencing of the ribosomal internal transcribed spacer (ITS) region has been used to positively identify all T. mentagrophytes isolates (rDNA). All T. mentagrophytes strains tested positive for SUB1, SUB2, SUB4, SUB6, and SUB7. While SUB5 was not found in any of the isolates, SUB3 was present in 90% of human and 100% of animal dermatophytosis samples. The presence of dermatophyte virulence factors, or SUB genes, is indicative of the existence of many dermatophyte species that share a common ancestor. However, the fact that our clinical isolates lacked the SUB5 gene suggests that not all SUB genes contribute to pathogenesis and infection.