PM substrates giving lowest levels of toxin production by C. difficile ATCC 9689.

aOD (750 nm) difference between C. difficile under certain PM substrate (condition) and the same substrate without C. difficile.bToxin concentrations in the CHO-k1 assay medium with C. difficile supernatant collected from different PM conditions, which were calculated from the average dye reduction rate by the CHO-k1 cells according to the equations in Table 1.cThe P values were obtained from t-test on the dye reduction rates of CHO-k1 cells in the presence or absence of C. difficile supernatants collected from different PM conditions.dAverage OD (750 nm) value of all uninoculated PM substrates from PM1–8.eThis value is a result of calculation based on dye reduction rate of CHO-k1 cells in the presence of PM substrates of PM1–8 without C. difficile inoculation. It is a measure of zero toxin.