A PARTICLE COUNTING IMMUNOASSAY FOR THE DIRECT-DETECTION OF CLOSTRIDIUM-DIFFICILE SEROGROUP SPECIFIC ANTIGEN IN FECAL SPECIMENS

The potential of a particle counting immunoassay (FACIA) for the direc t detection of Clostridium difficile serogroup G specific antigen in f aecal specimens was evaluated. F(ab'), fragments from a rabbit anti-se rogroup G antiserum were covalently coupled to carboxylated latex bead s. This reagent was mixed with acid extracts of faecal specimens and t he reaction was assayed with an optical counter which discriminated un agglutinated from agglutinated latex particles. Culture for C. diffici le, faecal cytotoxin detection, FACIA and serogrouping of C. difficile isolates were performed on 249 stools. Of the 71 culture-negative spe cimens, none gave a positive result in the cytotoxin assay or in FACIA . Faecal cytotoxin was detected in 100 of the 178 culture-positive spe cimens. FACIA was positive for 63 of the 71 faecal specimens that yiel ded serogroup G C. difficile on culture. FACIA gave negative results f or all other culture-positive stools tested with one exception, from w hich a serogroup A7 C. difficile strain was isolated. FACIA detection of serogroup G antigen in faecal specimens showed a sensitivity of 88. 7 %, a specificity of 99.7 %, a predictive value of a positive culture with a serogroup G strain of 98.4 %, and a predictive value for speci mens that were culture-negative for a serogroup G strain of 95.6 %. Th e results indicate that FACIA with specific antiserum is a rapid and r eliable method for detecting serogroup specific antigens of C. diffici le in faecal specimens. Clinical applications of the method are discus sed.