RESUMEN
As cepas de Escherichia coli do sorogrupo O145 são associadas principalmente ao patotipo E.coli produtor de toxina Shiga (STEC). No Brasil, cepas O145 são isoladas de casos de infecções humanas com relativa frequência. No entanto, a maioria são classificadas como EPEC atípicas (aEPEC), pois apresentam apenas o gene eae. A forte associação de STEC O145 com o subtipo 2f do gene stx2, que não é rotineiramente pesquisado no Brasil, sugere que estes isolados classificados como aEPEC poderiam representar cepas STEC portadoras de stx2f, ou cepas que perderam os genes stx por excisão de fagos. O objetivo deste estudo foi caracterizar as cepas de E. coli O145 em aspectos como potencial de virulência e diversidade genética. Avaliar a ocorrência de stx2f e outros marcadores de virulência diversos em uma coleção de 38 cepas O145, isoladas de infecções humanas (n=35), animais (n=1) e alimentos (n=2). A similaridade génetica e a diversidade clonal das cepas O145 foram avaliadas pelas técnicas de PFGE e MLST. Oito cepas apresentaram os genes stx sendo classificadas como STEC, seis cepas apresentaram bfpB classificadas como tEPEC e 22 cepas eae+ classificadas como aEPEC. Quatro cepas apresentaram stx2f, confirmando a hipótese de que alguns isolados O145 em nosso país são erroneamente identificados como aEPEC. Uma cepa apresentou stx1a, e três stx2a. As cepas apresentaram os genes fliCH28, fliCH4, fliCH34 e fliCH45. As cepas O145:H28 foram positivas para o subtipo eae (γ1), as O145:H34 eae (ι) e O145:H45 eae (µ). Em relação ao marcadores de virulência, ocorreram marjoritariamente nas cepas O145:H28, as cepas dos outros sorotipos apresentaram um baixa frequência de marcadores inclusive as cepas STEC com genótipo stx2f. A tipagem por PFGE revelou uma ampla diversidade genética entre as cepas O145. A tipagem por...(AU)
Escherichia coli strains of serogroup O145 are mainly associated with the Shiga toxin-producing E.coli (STEC) pathotype. In Brazil, O145 strains are isolated from cases of human infections with relative frequency. However, most are classified as atypical EPEC (aEPEC), as they have only the eae gene. The strong association of STEC O145 with the 2f subtype of the stx2 gene, which is not routinely investigated in Brazil, suggests that these isolates classified as aEPEC could represent STEC strains carrying stx2f, or strains that have lost the stx genes by phage excision. The aim of this study was to characterize E. coli O145 strains in aspects such as virulence potential and genetic diversity. To evaluate the occurrence of stx2f and other virulence markers in a collection of 38 O145 strains, isolated from human infections (n=35), animals (n=1) and foods (n=2). Genetic similarity and clonal diversity of O145 strains were evaluated by PFGE and MLST techniques. Eight strains showed the stx genes being classified as STEC, six strains had bfpB classified as tEPEC and 22 eae+ strains classified as aEPEC. Four strains showed stx2f, confirming the hypothesis that some O145 isolates in our country are misidentified as aEPEC. One strain showed stx1a, and three stx2a. The strains showed the genes fliCH28, fliCH4, fliCH34 and fliCH45. Strains O145:H28 were positive for the eae subtype (γ1), O145:H34 eae (ι) and O145:H45 eae (µ). Regarding virulence markers, they occurred mostly in strains O145:H28, strains of other serotypes showed a low frequency of markers, including STEC strains with genotype stx2f. PFGE typing revealed a wide genetic diversity among O145 strains. MLST typing in O145 strains revealed 11 distinct (STs). The strains of serotype O145:H28 presented STs 32, 137, 524 and 525 and (CC) 32, of serotype O145:H34, STs 526, 713 and 722, of serotype O145:H45, STs 4065 and 2331...(AU)
RESUMEN
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.
