Detection of Mixed Populations of Clostridium difficile from Symptomatic Patients Using Capillary-Based Polymerase Chain Reaction Ribotyping

Objective.To investigate the simultaneous occurrence of more than 1 Clostridium difficile ribotype in patients'' stool samples at the time of diagnostic testing.Methods.Stool samples submitted for diagnostic testing for the presence of toxigenic C. difficile were obtained for 102 unique patients. A total of 95 single colonies of C. difficile per stool sample were isolated on selective media, subcultured alongside negative (uninoculated) controls, and polymerase chain reaction (PCR) ribotyped using capillary gel electrophoresis.Results.Capillary-based PCR ribotyping was successful for 9,335 C. difficile isolates, yielding a median of 93 characterized isolates per stool sample (range, 69--95). More than 1 C. difficile ribotype was present in 16 of 102 (16%) C. difficile infection (CDI) cases; 2 of the 16 mixtures were composed of at least 3 ribotypes, while the remaining 14 were composed of at least 2.Conclusions.Deep sampling of patient stool samples coupled with capillary-based PCR ribotyping identified a high rate of mixed CDI cases compared with previous estimates. Studies seeking to quantify the clinical significance of particular C. difficile ribotypes should account for mixed cases of disease.