An unopened thioglycollate tube (*) showing no growth, a control tube showing positive growth (C), and samples from study groups 1–6 (numbered) at 1 week showing no growth (A). A sample of 10 mL of thioglycollate broth on the left showing retained sterility after being transferred to a 15-mL conical tube, a sample from study group 7 in the middle, and a sample from study group 8 on the right at 1 week showing no growth (B).