Detection of C. hominis and C. parvum at different ratios in mixed populations. (a) Analysis of mixed-species suspensions identified C. parvum DNA at all C. parvum/C. hominis ratios. Lane 1, molecular weight marker; lane 2, negative control; lane 3, C. hominis control; lane 4, C. parvum control; lanes 5 to 7, 1:99 ratio; lanes 8 to 10, 5:95 ratio; lanes 11 to 13, 10:90 ratio; lanes 14 to 16, 25:75 ratio; lanes 17 to 19, 50:50 ratio. (b) C. hominis DNA could not be detected by RFLP analysis at the majority of the ratios. The only exception was sporadic amplification in the samples containing C. hominis and C. parvum at a ratio of 5:95 (lanes 8 to 10).