Características fenotípicas e genotípicas de amostras de Escherichia coli 0157 produtoras de toxina Shiga

• Ano de defesa: 2006
• Autor(a) principal: Bastos, Flavia Correa [UNIFESP]
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de São Paulo (UNIFESP)
• Palavras-chave em Português: Escherichia coli; 0157:H7; Subtipos stx; Comportamento bioquímico; PFGE; Eletroforese em gel de campo pulsado; Toxina Shiga
• Link de acesso: http://repositorio.unifesp.br/handle/11600/9161

Shiga toxin-producing O157:H7 Escherichia coli has been identified as an important cause of hemorrhagic colites and Hemolytic Uremic Syndrome in many countries. Some studies conducted in Brazil have shown the presence of this serotype in human infections and in the animal reservoir. In the present study, a total of 38 E. coli O157 strains isolated in Brazil, Argentina, Chile, Colombia, United States and Uruguay from different sources was studied in regard to several phenotypic and genotypic characteristics. The detection of the stx genotype, the presence of other toxins (ehx and cdtV) and putative adhesin gene sequences (efa1, iha, lpfO113, lpfO157 saa and toxB) were identified by PCR. The stx variants were determined by RFLP-PCR. Several biochemical characteristics and the susceptibility to antimicrobial agents were identified by standard methods. Most (97.3%) of the strains carried stx2 alone or in association with stx1. Many combinations of stx genes occurred among strains of different sources. stx2stx2c was more frequently found among human strains isolated in Brazil and Argentina, while stx2c was more frequently found among animal strains. In the other hand, stx1 alone or in combination with stx2 was identified in 18.4% of strains isolated from animal and food. All strains were positive for eae-γ , efa1, ehx, iha, lpfO157 and toxB genes independent of their source and country, and presented similar biochemical behaviour, except for three strains that displayed urease activity, and one strain that did not decarboxylate lysine. All the strains carried the H7 flagellar antigen, thus belonging to serotype O157:H7. Different biotypes were identified among the strains, but 61% of them belong o only four biotypes. Fermentation of sorbitol was only observed in four of the 38 strains analysed. Most of the strains was sensitive to the 10 antimicrobial agents tested, but resistance to at least one antimicrobial agent was more commonly observed among bovine strains. A diversity of PFGE patterns was observed among the O157:H7 STEC strains by macrorestriction analysis of genomic DNA with XbaI. However, a high degree of similarity and many closely related subgroups (more than 80% of similarity) was identified among strains isolated from different origins and countries. Therefore, O157:H7 STEC strains isolated from human infections, animal reservoir and from food in Brazil and in different countries showed very similar profiles related to the phenotypic and genotypic characteristics analysed in the present study, and although some particular differences were detected, the presence of some clones was also identified among the strains.