Molecular diagnosis of Cryptosporidium from stool samples obtained from South African patients by a nested PCRRFLP procedure based on SSU rRNA gene sequences. A, Specific detection of Cryptosporidium spp. by nested PCR. Lane M, molecular weight markers; lanes 1–6, stool samples positive for Cryptosporidium after the nested PCR. B, Speciation of Cryptosporidium by DraII digestion of the nested PCR products. None of the sample was digested, indicating that all were either C. parvum or C. hominis. C, Speciation of Cryptosporidium by VspI digestion of the nested PCR products, showing that sample 5 is C. parvum, whereas the other samples were C. hominis. Ch is the C. hominis–positive control (Ch = 50 ng, Ch’ = 5 ng of genomic DNA), whereas Cp is the C. parvum–positive control. N is the negative control.