Extraction of Clostridium perfringens spores from bottom sediment samples

Two extraction-separation procedures were developed and evaluated for use in conjunction with the mCP membrane filter method for the enumeration of Clostridium perfringens spores in bottom sediments. In the more facile of the two procedures, a distilled-water suspension of the sediment sample is pulse sonicated for 10 s and allowed to settle. Portions of the supernatant are then removed for membrane filtration. This procedure is recommended for general use. The more complicated procedure is recommended for situations in which the presence of high levels of toxic materials is suspected or in which relatively low spore densities are present in fine silts. In this procedure, sonication is followed by a distilled water wash. The centrifuged sediment is resuspended in distilled water and mixed with the components of a two-phase separation system (50% polyethylene glycol in distilled water and 25% sucrose in 3 M phosphate buffer [pH 7.1]). After equilibration of the system and low-speed centrifugation, the top phase and interphase are removed, mixed, and membrane filtered. The recoveries of C. perfringens spores by the two procedures, when used in conjunction with the mCP method, were comparable to each other and significantly greater than those by the British most-probable-number method. It was estimated that more than 85% of the spores were recovered by the procedures. The precision of the sonicate-and-settle-mCP procedure was markedly better than that obtained theoretically by the most-probable-number method and approached that theoretically attributable to counting an average of 85 colonies on each of two plates.