# Hemolytic and Co-Hemolytic Activity of Trichophyton indotineae and Related Dermatophytes Isolated from Chronic and Recalcitrant Infections

## TL;DR

This study explores the hemolytic activity of Trichophyton indotineae and related fungi, which may contribute to chronic and hard-to-treat skin infections.

## Contribution

The study reveals high hemolytic activity in T. indotineae, offering new insights into its potential virulence mechanisms.

## Key findings

- 93.7% of dermatophyte isolates showed hemolytic activity, with T. indotineae being the most hemolytic at 97.4%.
- Co-hemolytic activity was rare, observed in only 3.1% of isolates.
- Hemolysis was more detectable on ovine erythrocyte agar than equine erythrocyte agar.

## Abstract

Dermatophyte infections have evolved in both clinical presentation and etiological profiles, with chronic, recurrent, and widespread forms becoming increasingly prevalent and therapeutically challenging over the past decade. These infections are predominantly caused by Trichophyton indotineae (ITS genotype VIII), a member of the Trichophyton mentagrophytes complex. The virulence mechanisms of T. indotineae remain poorly understood. To elucidate potential pathogenic factors, we investigated hemolytic and co-hemolytic (CAMP-like) activities in dermatophytes associated with recalcitrant dermatophytosis. A total of 127 isolates (117 T. indotineae, 5 T. rubrum, 3 T. tonsurans, and 2 Microsporum canis) were examined using Columbia agar supplemented with 5% ovine (COA) or equine erythrocytes (CEA). Hemolysis was more consistently observed on COA (119 isolates) than on CEA (44 isolates) following 7-day incubation at 27 °C. Additional incubation at 36 °C up to 7 days was required to enhance hemolysis detection on CEA. Overall, 93.7% of isolates exhibited hemolytic activity, whereas only 3.1% demonstrated co-hemolytic activity. Among T. indotineae isolates, 97.4% were hemolytic. These findings underscore the importance of characterizing virulence traits in dermatophytes. Additional studies are needed to clarify the role of hemolysis in chronic and recalcitrant infections, with the goal of identifying novel therapeutic targets.

The online version contains supplementary material available at 10.1007/s11046-026-01062-9.