Resumo

Introduction: The foodborne disease caused by Salmonella is a major health problem worldwide. Among more than 2500 serovars, S. Typhimurium has been one of the most frequent isolated in Brazil and worldwide. Due to the great importance of Salmonella, many phenotypic and genotypic studies are used to better elucidate its epidemiology. However, there are few molecular typing studies of S. Typhimurium strains isolated in Brazil. The aim of this study was to type by Pulsed-Field Gel Electrophoresis (PFGE) S. Typhimurium strains isolated from humans and food during 22 years in Brazil. Materials and methods: A total of 47 S. Typhimurium strains, isolated from humans (41) and food (06), between 1983 and 2005 in some cities of Sao Paulo State, were characterized by PFGE using 40U XbaI enzyme. The plugs preparation and the run were the ones described in PulseNet. Data were analyzed by BioNumerics 7 version (Applied Maths) software and the similarity dendrogram constructed by UPGMA method and DICE similarity coefficient with tolerance of 1.5. Results: The 47 S. Typhimurium strains were divided in three clusters, denominated A, B and C. Cluster A comprised 12 strains, isolated from humans between 1983 and 1986, exhibiting a genetic similarity ≥ 60.6%. In cluster B nine strains, isolated from humans between 1983 and 1984, presenting a genetic similarity ≥ 57.3% were grouped. Cluster C comprised 26 strains that could be divided in three subclusters designated C1, C2 and C3. In subcluster C1, 14 strains were grouped being three isolated from food and 11 isolated from humans between 1983 and 2003 and exhibiting a genetic similarity ≥ 71.6%. In subcluster C2, 10 strains were grouped being three isolated from food and seven isolated from humans between 1985 and 2005 with a genetic similarity ≥ 81.6%. In subcluster C3, only two strains isolated from humans of 1984 and 1985 were grouped, which exhibited a genetic similarity ≥ 76.2%. The C1, C2 and C3 subclusters presented a similarity of 58.6%. Conclusion: The S. Typhimurium studied showed to be genotypically diverse. Specifically the strains isolated before 1986 were genetically more diverse in comparison with those ones isolated after the 1990´s which might suggest the selection of a more adapted S. Typhimurium clone after S. Enteritidis becoming the most prevalent serovar in Brazil.