Salmonella enteritidis phage types 1 and 4: Pheno- and genotypic epidemiology of recent outbreaks in Finland

In the 1990s, Salmonella enterica subsp. enterica serovar Enteritidis has c aused 15 outbreaks in I;inland; 12 of them were caused by phage type 1 (PT1 ) and PT1. Thus far, there has been no clear evidence as to the source of t hese Salmonella Enteritidis PT1 and PT4 strains, so it was necessary to try to characterize them further. Salmonella Enteritidis PT1 (n = 57) and PT4 (n = 43) isolates from different sources were analyzed by genomic pulsed-fi eld gel electrophoresis (PFGE), plasmid profiling, and antimicrobial resist ance testing to investigate the distribution of their subtypes in Finland. It was also hoped that this investigation would help in identifying the sou rces of the infections, especially the sources of the outbreaks caused by P T1 and PT1 in the 1990s. The results showed that both PFGE and plasmid prof iling, but not antimicrobial susceptibility testing, were capable of differ entiating isolates of Salmonella Enteritidis PT1 and PT4. By genotypic meth ods, it was possible to divide both PT1 and PT-I isolates into 12 subtypes. It could also be shown that all PT1 outbreak isolates were identical and, at least with this collection of isolates, that the outbreaks did not origi nate from the Baltic countries or from Russia, where this phage type predom inates. It was also established that the outbreaks caused by PT 1 all had d ifferent origins. Valuable information for future investigations was pained on the distribution of molecular subtypes of strains that originated from the tourist resorts that are popular among Finns and of strains that were i solated from livestock.