Forty-one strains of Bacteroides fragilis, 20 strains of other Bacteroides species and 14 strains of other genera were examined by the indirect immunofluorescent assay (IFA) using anticapsular serum. The sixty-one Bacteroides strains were 'O' serotyped by direct agglutination tests using absorbed antisera raised against 23 strains, each with a different 'O' antigenic determinant. All 41 B. fragilis strains tested were positive by IFA with the anticapsular serum, but apart from one strain of B. distasonis, none of the remaining 19 strains of other bacteroides, i.e. B. thetaiotaomicron, B. distasonis, B. vulgatus, B. ovatus, B. melaninogenicus group and B. ureolyticus, and none of the 14 other bacterial species examined were positive. The majority of strains of saccharolytic bacteroides tested reacted with one of the 23 'O' antisera and were designated as a specific 'O' serotype; a few Bacteroides strains had multiple agglutination reactions indicating the presence of multiple antigenic determinants. All 'O' serotypes gave positive IFA tests with their homologous 'O' antisera. Common capsular determinants and 'O' antigenic determinants appear to exist on the same strains of B. fragilis. Serological typing of B. fragilis and related species would be useful in epidemiological studies.

Antigens, Bacterial↗

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Epidemiologic markers of Clostridium difficile.

A wide range of epidemiologic markers have been identified for Clostridium difficile. These markers are based on phenotypic characteristics of the organism, such as antibiotic resistance, bacteriocin or bacteriophage susceptibility, electrophoretic protein patterns, and immunologic markers. Methods for determining genetic markers include plasmid and DNA restriction endonuclease analysis and ribosomal RNA restriction patterns. These methods have been applied to various degrees in epidemiologic studies and have contributed to a better understanding of C. difficile-associated disease. The method based on the use of [35S]methionine-labeled proteins and the development of an automated scanner with computer analysis made possible the recognition of 15 distinct types of C. difficile, based on the major radiolabeled protein patterns. These proteins were strain-specific and immunogenic, as demonstrated by immunoblotting and DNA restriction endonuclease analysis. Epidemiologic studies revealed cross-infection among patients, nosocomial acquisition, and a direct relation between symptoms and type of C. difficile. The development of DNA probes based on antibiotic resistance genes, toxin A, and cloned specific common antigens is discussed.

Antigens, Bacterial↗