Abstract
Since no recent data characterizing Shiga toxin-producing E. coli (STEC) from human infections in Brazil are available, the present study aimed to investigate serotypes, stx genotypes, and accessory virulence genes, and also to perform pulsed-field gel electrophoresis (PFGE) and multi-locus sequence typing (MLST) of 43 STEC strains recovered from 2007 to 2017. Twenty-one distinct serotypes were found, with serotype O111:H8 being the most common. However, serotypes less frequently reported in human diseases were also found and included a hybrid STEC/ETEC O100:H25 clone. The majority of the strains carried stx1a as the sole stx genotype and were positive for the eae gene. Regarding the occurrence of 28 additional virulence genes associated with plasmids and pathogenicity islands, a diversity of profiles was found especially among the eae-harboring strains, which had combinations of markers composed of up to 12 distinct genes. Although PFGE analysis demonstrated genetic diversity between serotypes such as O157:H7, O111:H8, O26:H11, O118:H16, and O123:H2, high genetic relatedness was found for strains of serotypes O24:H4 and O145:H34. MLST allowed the identification of 17 distinct sequence types (STs) with ST 16 and 21 being the most common ones. Thirty-five percent of the strains studied were not typeable by the currently used MLST approach, suggesting new STs. Although STEC O111:H8 remains the leading serotype in Brazil, a diversity of other serotypes, some carrying virulence genes and belonging to STs incriminated as causing severe disease, were found in this study. Further studies are needed to determine whether they have any epidemiological relevance.
Highlights
Shiga toxin-producing Escherichia coli (STEC), one of the six recognized pathotypes of diarrheagenic E. coli (DEC) [1], is a worldwide foodborne pathogen responsible for causing enteric infections in humans, which can vary from mild and self-limiting diarrhea to exacerbated clinical conditions such as bloody diarrhea (BD) and hemorrhagic colitis [2]
Much evidence indicates that the clinical prognosis in the Shiga toxin-producing E. coli (STEC) infections can be influenced by the presence of additional virulence factors beyond the Shiga toxin subtype produced by a given strain [10]
Taking these points into consideration and the fact that there are no recent studies about STEC pathogens from humans in Brazil, this study aimed to perform a comprehensive characterization regarding the presence of several virulence genotypic markers and the molecular typing of strains of clinical sources, recovered from surveillance programs conducted in Brazil, in a range of time spanning the years from 2007 to 2017
Summary
Shiga toxin-producing Escherichia coli (STEC), one of the six recognized pathotypes of diarrheagenic E. coli (DEC) [1], is a worldwide foodborne pathogen responsible for causing enteric infections in humans, which can vary from mild and self-limiting diarrhea to exacerbated clinical conditions such as bloody diarrhea (BD) and hemorrhagic colitis [2]. Patients infected with STEC may develop hemolytic uremic syndrome (HUS), which is characterized by acute renal failure, hemolytic anemia, and thrombotic thrombocytopenic purpura [3]. HUS is a major cause of permanent renal injury and can be fatal in a variable proportion of cases but especially in children [4]. The production of Shiga toxins (Stx) is the main virulence property associated with STEC pathogens [2]. These toxins comprise two major antigenically distinct groups, Stx and Stx, and each group has toxin subtypes. For Stx, there are subtypes 1a, 1c, and 1d, while for Stx there are currently subtypes 2a, 2b, 2c, 2d, 2e, 2f, 2g, 2h, 2i and 2k [5,6,7]
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