Small portions of fecal matter were vortexed for 15 seconds in stool suspension buffer, 2 ml 0.9% saline with glass beads (samples 1 to 93) or 5 ml of M199 containing 15.6 mg of dihydrostreptomycin, 15,625 U of Penicillin G, and 156 U of Mycostatin and 0.1 volume (v/v) of chloroform (samples 101-192). Suspensions were clarified by centrifugation at 2,5006g for 10 min and stored at 220uC until use.