Identification of persistent subtypes of Campylobacter jejuni by pulsed-field gel electrophoresis in Finland.

The genetic diversity of Campylobacter jejuni strains isolated from Finnish patients was studied by typing 508 strains by pulsed-field gel electrophoresis: 311 were isolated from domestically acquired infections and 197 from travel-related infections. The strains were systematically selected from a larger collection of previously serotyped strains isolated during two 1-year sampling periods. The four most common SmaI profiles accounted for 45% of the domestic strains but only 3% of the travel-related strains. Of the domestic strains, 69% belonged to SmaI subtypes found during both sampling periods. The predominating SmaI subtypes and strains that were not digested by SmaI were typed by KpnI. Analyzing the temporal diversity of the pulsed-field gel electrophoresis profiles revealed six common persistent SmaI/KpnI subtypes among the domestic strains. Five of them have been identified in cattle, and two in chickens with a temporal association with human infections.