Abstract
A HindIII restriction endonuclease analysis (REA) typing system for total genomic Clostridium difficile DNA including a rapid and efficient method of DNA extraction and a scheme for organizing unique electrophoretic DNA band patterns was developed. REA typing was performed by two extraction methods for 1,965 C. difficile isolates obtained from patients with symptomatic C. difficile disease, asymptomatic patients who were C. difficile culture positive, and environmental surfaces. This isolate collection yielded 206 unique REA types, which were organized into 75 groups. A reference strain representing each unique REA type was chosen for DNA band pattern comparisons, cytotoxin testing, and plasmid analysis. The DNA band patterns utilizing a guanidine thiocyanate-EDTA-Sarkosyl DNA extraction method were 94% reproducible, while the original and sporadically problematic diethyl pyrocarbonate-sodium dodecyl sulfate DNA extraction method was 98% reproducible when readable patterns were obtained. Reference strains from 43 of the 75 groups were cytotoxin positive, 28 groups were cytotoxin negative, and 4 groups included both toxigenic and nontoxigenic strains. Cytotoxicity of isolates with a particular REA type was always consistent with the toxicity of the reference strain for that type. REA typing was able to discriminate strain differences within types identified by the immunoblot (89 isolates), bacteriophage-bacteriocin (44 isolates), and ribotyping (23 isolates) methods. REA typing is a sensitive, discriminating, reproducible, and rapid method for differentiating C. difficile strains and is suitable for large-scale epidemiologic studies.