Colonies of T. mentagrophytes (left), T. rubrum (center) and T. violaceum (right) showing differential responses on Bromocresol Purple Milk Solids Glucose agar (7 d). T. mentagrophytes shows unrestricted growth with alkaline (purple) colour change, T. rubrum shows restricted growth with no pH change, and T. violaceum produces weak growth accompanied by clearing of the milk solids and a purple colour change.