MOLECULAR EPIDEMIOLOGY OF 2 INTERNATIONAL SPROUT-BORNE SALMONELLA OUTBREAKS

Sprout-borne Salmonella outbreaks in Finland have increased during the last 10 years, The latest two were caused by Salmonella enterica sero var Bovismorbificans (antigenic structure 6,8:r:1,5) in 1994 and S. en terica serovar Stanley (4,5, 12:d:1,2) in 1995, In this study, the res triction fragment length polymorphism of genomic DNA after pulsed-fiel d gel electrophoresis (PFGE) and antimicrobial resistance profiles of the outbreak and nonoutbreak strains were compared, In each separate o utbreak, the PFGE patterns of the outbreak strains (40 strains of S. e nterica serovar Bovismorbificans and 28 strains of S. enterica serovar Stanley) after digestion of genomic DNA with restriction enzyme XbaI were indistinguishable from each other but differed clearly from those of the nonoutbreak strains (26 strains of S. enterica serovar Bovismo rbificans and 40 strains of S. enterica serovar Stanley), The restrict ion enzyme XhoI did not differentiate the outbreak and nonoutbreak str ains, The S. enterica serovar Stanley strains associated with the outb reak also had a unique antimicrobial resistance pattern, whereas all S . enterica serovar Bovismorbificans strains, both outbreak and nonoutb reak strains, were sensitive to all antimicrobial agents tested, Thus, the molecular typing confirmed that the S. enterica serovar Bovismorb ificans outbreak isolates from humans and sprout salad were identical and strongly supported the epidemiological finding that S. enterica se rovar Stanley outbreak isolates also originated from contaminated alfa lfa seeds, It also confirmed that the sources of similar outbreaks in Sweden in 1994 caused by S. enterica serovar Bovismorbificans and in t he United States in 1995 caused by S. enterica serovar Stanley and the source of the Finnish outbreaks were common.