Molecular typing and long-term comparison of Clostridium difficile strainsby pulsed-field gel electrophoresis and PCR-ribotyping

Thirty-two related and 68 unrelated isolates of Clostridium difficile, isol ated in different Italian hospitals since 1987, were analysed by PFGE and P CR-ribotyping to investigate their genetic relatedness. The isolates were c lassified into 28 groups by PFGE and 20 ribotypes by PCR-ribotyping. ii sin gle clone of C, difficile was recognised as the cause of three geographical ly and chronologically distant outbreaks, The correlation between PFGE and PCR-ribotyping results was good, with agreement for 77 (84%) of the 92 isol ates typed by both methods. However, among sporadic isolates the discrimina tory power of PFGE was more evident. Eight isolates that were untypable by PFGE could be analysed by PCR-ribotyping. The dendrograms generated showed that the genetic relatedness of the C, difficile isolates obtained by both techniques was comparable. The majority of the isolates in recent years app eared to be genetically unrelated to isolates from past infections. However , two clonal groups identified in all time periods had a common origin and this seems to indicate that they share some advantageous biological charact eristics. The constant monitoring of C, difficile epidemiology will allow a cquisition of further important data on this nosocomial pathogen.