Purpose: Early detection of Clostridium in food and water is, therefore, important to control outbreaks.
Methods: To facilitate detection, the new chromogenic medium, the CP ChromoSelect Agar, for enumeration and differentiation of Clostridium sp., in particular Clostridium perfringens, is used in aqueous samples.
Three media types (mCP,TSCF and the new CP Agar) were evaluated for recovery of C. perfringens in different surface water samples. Using a membrane filtration technique on 139 water samples, 131 samples (94.2%) were found positive for C. perfringens in at least one of the culture media. Green colored colonies on the new Agar (cf. Figure 2) were counted as presumptive C. perfringens isolates.
Results: Out of 483 green colonies on the new Agar, 96.3% (465 strains, indole negative) were identified as C. perfringens, 15 strains (3.1%) were indole positive and were identified as C. sordelli, C. bifermentans or C. tetani. Only 3 strains (0.6 %) gave false positive results and were identified as C. fallax, C. botulinum, and C. tertium. Variance analysis of the data showed statistically no significant differences in the counts obtained between media used in this work. In general, the identification of typical and atypical colonies isolated from all media demonstrated that the new Agar was the most useful medium for C. perfringens recovery in water samples. The new Agar avoids the disadvantages of m-CP agar, such as, the presence of ammonia that prevents subculturing the C. perfringens colonies, the too-selective nature of m-CP agar, and the evanescence of the red color of colonies after the addition of ammonia, which makes further confirmation impossible.
Significance: This chromogenic media is more reliable and easier to handle than m-CP and TSC agars. The color does not diffuse in the agar and confirmation is not required since the green coloration is specific for C. perfringens.