Clostridium difficile is an opportunistic pathogen that causes a spectrum of disease ranging from antibiotic-associated diarrhea to pseudomembranous colitis. Although the disease was first described in 1893, the etiologic agent was not isolated and identified until 1978. Since clinical and pathological features of C. difficile-associated disease are not easily distinguished from those of other gastrointestinal diseases, including ulcerative colitis, chronic inflammatory bowel disease, and Crohn's disease, diagnostic methods have relied on either isolation and identification of the microorganism or direct detection of bacterial antigens or toxins in stool specimens. The current review focuses on the sensitivity, specificity, and practical use of several diagnostic tests, including methods for culture of the etiologic agent, cellular cytotoxicity assays, latex agglutination tests, enzyme immunoassay systems, counterimmunoelectrophoresis, fluorescent-antibody assays, and polymerase chain reactions.

Sniffing out atherosclerosis Olfactory receptors are best known for their presence in the nose and their role in detecting smells, but they are also present in other tissues and perform additional biological functions. For example, vascular macrophages involved in the pathogenesis of atherosclerosis express multiple subtypes of olfactory receptors. Orecchioni et al . focused on olfactory receptor 2, a receptor for the compound octanal, and identified its contribution to atherosclerosis pathogenesis and the formation of atherosclerotic plaques (see the Perspective by Rayner and Rasheed). The authors show that most of the octanal was not directly derived from the diet, but rather was generated as a by-product of lipid peroxidation, suggesting a potential pathway for intervention. —YN

Cytotoxin B of C. difficile was highly purified by selective ammonium sulfate precipitation, Biogel A5m chromatography, phenyl boronate hydrophobic interaction chromatography and ultracentrifugation. The final cytotoxic product had a specific activity of 7.8 × 108 protein and showed a single protein band with an estimated molecular weight of 163000 when subjected to SDS‐PAGE. Immunoelectrophoresis of the final product showed a single precipitin arc. The addition of cytotoxin B to imidazole‐HCl buffer (pH 7.4) containing MgSO4, KCl and the substrate 2‐phosphoglycerate resulted in the formation of phosphoenolpyruvate as demonstrated by spectrophotometric analysis. Phosphoglycerate conversion was absent when the cytotoxin was heat‐inactivated of reacted with specific antitoxin prior to assay.

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