Diagnosis of systemic candidiasis by enzyme immunoassay detection of specific antibodies to mycelial phase cell wall and cytoplasmic candidal antigens

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Abstract
Diagnosis of systemicCandida infections was attempted by the use of an enzyme-linked immunosorbent assay (EIA) to detect IgG antibodies towards cell wall-bound and cytoplasmic candidal antigens. Cell wall antigens were sequentially solubilized by treatment of germinated blastoconidia ofCandida albicans (ATCC 26555 strain) with β-mercaptoethanol (βME extract) and digestion with Zymolyase 20T, a β-glucanase preparation (Zymolyase extract). Protoplasts obtained after treatment with Zymolyase were osmotically lysed (cytoplasmic antigens). Sera were obtained from patients with systemic (n=28) and superficial (n=46) candidiasis. Control sera were obtained from normal healthy individuals (n=31) and from hospitalized patients at low (n=36) and at high (n=13) risk of developing systemic candidiasis yet showing no symptoms of candidal infection. Detection of antibodies in crude sera samples by EIA using all of these antigenic extracts was highly specific (98–100 %), but sensitivity of the method was low (3.5–17.8 %). However, adsorption of sera with latex microspheres coated with purifiedCandida mannan in order to selectively remove antimannan antibodies prior to EIA improved the diagnostic efficiency of this test. Improvement was particularly noticeable when the βME extract was used as antigenic preparation, yielding a sensitivity of 89.2 % and a specificity of 98.6 %.