DIFFERENTIATION OF SALMONELLA SEROVAR INFANTIS ISOLATES FROM HUMAN AND ANIMAL SOURCES BY FINGERPRINTING IS200 AND 16S RRN LOCI

We genotyped Salmonella serovar infantis (referred to as S. infantis), which is the most widespread serovar among animals and the third most common cause of human salmonellosis in Finland. Molecular fingerprint ing of the 16S rrn locus and the Salmonella-specific insertion sequenc e IS200 was used to type the 131 isolates originating from the main so urces of S. infantis infection. The number of IS200 elements in S. inf antis varied from zero to seven; three or more copies were present in 97% of the isolates, and 71% had four copies. There were four conserve d chromosomal positions of IS200, which allowed us to group the isolat es into three major clonal groups. We defined 11 unique IS200 profiles and five different ribotypes which, in combination, generated 15 geno types highly restricted to the infection sources: 8 genotypes were typ ical of isolates from broiler chickens and cattle and seven genotypes were typical of isolates from humans. The eight genotypes of isolates from chickens represented two clonal groups which were differentially associated with chicken-producing companies. The typing scheme allows efficient discrimination between isolates from various infection sourc es and within sources and, therefore, provides a unique molecular tool for use in the study of the epidemiology of S. infantis infection.