a microscope for detection of fungal elements. T. rubrum cannot be distinguished from other dermatophytes in this direct examination. It can be distinguished in vitro from other dermatophytes by means of characteristic micromorphology in culture, usually consisting of small, tear-drop-shaped microconidia, as well as its usual blood-red colony reverse pigmentation on most growth media. In addition, the Bromocresol purple (BCP) milk solid glucose agar test can be used to distinguish it. Different Trichophyton species release different amounts of ammonium ion, altering the pH of this medium. In this test, medium supporting T. rubrum remains sky blue, indicating neutral pH, until 7 to 10 days after inoculation. In primary outgrowth on Sabouraud dextrose agar with cycloheximide and antibacterials, contaminating organisms may cause confusion, as T. rubrum colonies deprived of glucose by competing contaminants may grow without forming the species' distinctive red pigment. Both antibiotic-resistant bacteria and saprotrophic fungi may outcompete T. rubrum for glucose if they contaminate the sample. Red pigment production can be restored in such contaminated isolates using casamino acids erythritol albumin agar (CEA). T. rubrum cultures can be isolated on both cycloheximide-containing media and cycloheximide-free media. The latter are conventionally used for the detection of nail infections caused by non-dermatophytes such as Neoscytalidium dimidiatum. A skin test is ineffective in diagnosing active infection and often yields false negative results. Pathology Trichophyton rubrum is rarely isolated from animals. In humans, men are more often infected than women. Infections can manifest as both chronic and acute forms. Typically T. rubrum infections are restricted to the upper layers of the epidermis; however, deeper infections are possible. Approximately 80–93% of chronic dermatophyte infections in many parts of the developed world are thought to be caused by T. rubrum including cases of tinea pedis(foot), tinea unguium(nail), tinea manuum(hand), tinea cruris(groin), and tinea corporis(arms and leg), as well as some cases of tinea barbae(beard). Trichophyton rubrum has also been known to cause folliculitis in which case it is characterized by fungal element in follicles and foreign body giant cells in the dermis. A T. rubrum infection may also form a granuloma. Extensive granuloma formations may occur in patients with immune deficiencies (e.g. Cushing syndrome). Immunodeficient neonates are susceptible to systemic T. rubrum infection. Trichophyton rubrum infections do not elicit strong inflammatory responses, as this agent suppresses cellular immune responses involving lymphocytes particularly T cells. Mannan, a component of the fungal cell wall, can also