Immunological methods for the detection of structural components and metabolites of bacteria and fungi in blood

Abstract

This review compares the clinical usefulness of immunological methods for the detection of structural components and metabolites of bacteria and fungi. Bacterial antigens (especially those of Mycobacterium, Neisseria, Staphylococcus aureus, Yersinia enterocolitica, Escherichia coli, Salmonella, Chlamydia, and Brucella) are best detected by enzyme-linked immunosorbent assay. Methods involving antibodies are more expensive and are effective only when performed in series. The detection of antibodies that recognize S aureus teichoic acid merely confirms the presence of a metastatic complication. Tissue invasion by Candida albicans is not yet reliably detectable by the presence of a specific antigen. Simple, but not completely reliable methods are available such as the latex test for mannans detection and/or agglutination with liposomes for detecting 48-kDa cytoplasmic protein antigen and an assay for detecting enolase antigen. A latex agglutination test has also been developed for the mannans antigen of Aspergillus and for Cryptococcus neoformans capsular polysaccharide; the latter test is more cost effective. The sensitivity of both tests is improved by serial assays. A negative finding with hemagglutination-based antibody tests rules out C albicans infection, and titers of 1/640 or higher have been associated with disseminated infection by Aspergillus. Concentrations of C albicans blastopore antigen antibodies higher than 400 IU/ml can be seen in disseminated candidiasis. High concentrations of endotoxin are indicative of imminent septic shock. Some biological indicators (C reactive protein, angiotensin converting enzyme, fibronectin, elastase-alpha 1-antitrypsin complex, tumor necrosis factor and interleukin-6) have been used to rule out a bacterial cause of fever