Dermatophytes can trigger cooperative (CAMP-like) haemolytic reactions

Dermatophytes usually grow on skin that is also colonized by bacteria. Therefore, a possible interaction between dermatophytes and bacteria is of potential relevance for the pathogenesis of skin infections. Cell membranes contribute substantially to epidermal barrier function. Erythrocyte haemolysis is a model commonly used to study membrane-damaging effects of microbial factors. Cooperative (CAMP-like) haemolytic reactions are known from distinct bacteria, but not from dermatophytes and bacteria.

To investigate CAMP-like reactions of dermatophytes.

Species of dermatophytes representing the genera Microsporum, Trichophyton and Epidermophyton, erythrocytes from sheep, horse and cattle, cultures of Staphylococcus aureus, S. intermedius, Listeria ivanovii, S. hyicus and S. epidermidis, and cell-free supernatants of bacterial cultures were used to search for cooperative haemolytic effects in in vitro agar diffusion assays.

A cooperative (CAMP-like) haemolytic reaction was identified for all dermatophytes tested. Using erythrocytes from sheep and cattle, pretreated with a sphingomyelinase from S. aureus, S. intermedius or L. ivanovii, the fungi induced a distinct zone of complete haemolysis on solid media and in a diffusion test. No CAMP reaction could be detected using S. hyicus or S. epidermidis as a first-step agent or with equine erythrocytes. The lytic reaction of the CAMP-cohaemolysin derived from dermatophytes was always separate from the zone of complete haemolysis, indicating two different cytolytic factors.

Our results show, for the first time, that in principle a CAMP-like effect can occur with dermatophtyes. This is a new observation of potential relevance for the pathogenesis of skin infections. The membrane-damaging factors released by dermatophytes should be further analysed.