|821-1||Molecular typing of Salmonella Infantis strains isolated from humans and food in Brazil|
|Autores:||Fernanda de Almeida (FCFRP-USP - Fac. Ciências Farmacêuticas de Ribeirão Preto - USP) ; André Pitondo-silva (FCFRP-USP - Fac. Ciências Farmacêuticas de Ribeirão Preto - USP) ; Maria Aparecida de Oliveira (CLRRP-IAL - Centro Lab. Regional Ribeirão Preto - Instituto Adolfo Lutz) ; Juliana Pfrimer Falcão (FCFRP-USP - Fac. Ciências Farmacêuticas de Ribeirão Preto - USP) |
The foodborne disease caused by Salmonella is a major health problem worldwide. Among more than 2500 serovars, S. Infantis has been one of the 15 most isolated serovars in Brazil and in several countries. Despite its clinical importance, little is known about the epidemiology of S. Infantis in Brazil. The aims of this study were to type S. Infantis strains isolated from humans and food by different molecular techniques and compare the discriminatory power of the methodologies used. A total of 35 S. Infantis strains, isolated from humans (25) and food (10), between 1984 and 2009 in several cities of Sao Paulo, were characterized by ERIC-PCR (Enterobaterial Repetitive Intergenic Consensus PCR), PFGE (Pulsed-Field Gel Electrophoresis) using XbaI and SpeI enzymes. Only bands between 298 and 4072 bp were included in the ERIC-PCR analysis and between 48.5 and 582.0 Kb in PFGE. Data were analyzed by BioNumerics 5.1 (Applied Maths) software and the similarity dendrogram constructed by UPGMA method and DICE similarity coefficient. Moreover, 16 strains of S. Infantis were studied by MLST following the methodology described in the S. enterica MLST website (http://mlst.ucc.ie/mlst/dbs/Senterica). The housekeeping genes purE, aroC, sucA, hemD, hisD, dnaN and thrA were sequenced in each strain and a consensus sequence was obtained by Chromas Pro 1.5 (Technelysium Pty LTDA). Alleles and sequence types (STs) were identified using MLST database. The similarity diagram was constructed by eBURSTv3. The discrimination indexes (DI) of ERIC-PCR and PFGE were calculated based in a variation of the Simpson’s diversity index. By ERIC-PCR 34 S. Infantis exhibited a high genetic similarity ≥ 84.5% and by PFGE 32 strains a similarity ≥ 70.2%. Also, MLST showed a high clonal similarity among strains which all presented the same ST (ST32). The discrimination indexes were 0.859 for ERIC-PCR and 1.0 for PFGE techniques. In conclusion, the S. Infantis studied were genetically closely related, suggesting that they descended from a common ancestor that has changed little over 25 years in Brazil. Furthermore, the cross contamination between strains from food and sick humans indicates that control measures of S. Infantis still need improvement in this country.
Palavras-chave: ERIC-PCR, MLST, PFGE, Salmonella Infantis