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 caused 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 these 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-field gel electrophoresis (PFGE), plasmid profiling, and antimicrobial resistance testing to investigate the distribution of their subtypes in Finland. It was also hoped that this investigation would help in identifying the sources of the infections, especially the sources of the outbreaks caused by PT1 and PT1 in the 1990s. The results showed that both PFGE and plasmid profiling, but not antimicrobial susceptibility testing, were capable of differentiating isolates of Salmonella Enteritidis PT1 and PT4. By genotypic methods, 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 originate from the Baltic countries or from Russia, where this phage type predominates. It was also established that the outbreaks caused by PT 1 all had different 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 isolated from livestock.