Detecting Clostridium difficile toxins by toxigenic culture

Abstract

Most clinical laboratories often use enzyme immunoassay (EIA) as a rapid test for the diagnosis of Clostridium difficile infection (CDI). However, its sensitivity of detecting C. difficile toxins is insufficient for diagnosis. Therefore, toxigenic culture (TC) can play an important role in diagnosing cases of CDI. We evaluated the usefulness of TC compared with the detection of the toxin B gene by polymerase chain reaction (PCR), and then designed an algorithm that uses TC for the laboratory testing of CDI to improve the sensitivity of detecting toxins. We found that some of the media used for culture and bacterial concentration affected the results of TC. Compared with the results by PCR, the sensitivity of TC was 100% when CCMA-EX culture medium and a bacterial concentration of 4.0 McF were used. On the other hand, the sensitivity decreased to 79% when chocolate agar and a bacterial concentration of 3.0 McF were used for TC. The specificity of both groups was 100%. These experimental results indicate that it is important to determine which medium and how much concentration of bacterial suspension should be used to reduce the number of false negative results. Standardized procedures are needed for the performance of TC by laboratories.