A G M Gonzalez1, A M F Cerqueira2, B E C Guth3, C A Coutinho4, M H T Liberal5, R M Souza5, J R C Andrade4. 1. Departamento de Bromatologia, Universidade Federal Fluminense, Niterói, Brasil. aliceg@id.uff.br. 2. Departamento de Microbiologia e Parasitologia, Universidade Federal Fluminense, Niterói, Brasil. 3. Departamento de Microbiologia, Imunologia e Parasitologia, Universidade Federal de São Paulo, São Paulo, Brasil. 4. Departamento de Microbiologia, Imunologia e Parasitologia, Universidade do Estado do Rio de Janeiro, Rio de Janeiro, Brasil. 5. Centro Estadual de Pesquisa em Sanidade Animal, Pesagro-Rio, Niterói, Brasil.
Abstract
AIM: The occurrence of virulence markers, serotypes and invasive ability were investigated in Shiga toxin-producing Escherichia coli (STEC) isolated from faecal samples of healthy dairy cattle at Rio de Janeiro State, Brazil. METHODS AND RESULTS: From 1562 stx-positive faecal samples, 105 STEC strains were isolated by immuno-magnetic separation (IMS) or plating onto MacConkey agar (MC) followed by colony hybridisation. Fifty (47·6%) strains belonged to nine serotypes (O8:H19, O22:H8, O22:H16, O74:H42, O113:H21, O141:H21, O157:H7, O171:H2 and ONT:H21). The prevalent serotypes were O157:H7 (12·4%), O113:H21 (6·7%) and O8:H19 (5·7%). Virulence genes were identified by polymerase chain reaction (PCR). E-hlyA (77·1%) was the more prevalent virulence marker, followed by espP (64·8%), saa (39%), eae (24·8%) and astA (21·9%). All O157:H7 strains carried the γ (gamma) variant of the locus of enterocyte effacement (LEE) genes and the stx2c gene, while the stx1/stx2 genotype prevailed among the eae-negative strains. None of the eae-positive STEC produced the localized adherence (LA) phenotype in HEp-2 or Caco-2 cells. However, intimate attachment (judged by the fluorescent actin staining test) was detected in some eae-positive strains, both in HEp-2 (23·1%) and in Caco-2 cells (11·5%). Most strains (87·5%) showed 'peripheral association' (PA) adherence phenotype to undifferentiated Caco-2 cells. Twenty-five (92·6%) of 27 strains invaded Caco-2 cells. The highest average value of invasion (9·6%) was observed among the eae-negative bovine strains from serotypes described in human disease. CONCLUSION: Healthy dairy cattle is a reservoir of STEC carrying virulence genes and properties associated with human disease. SIGNIFICANCE AND IMPACT OF THE STUDY: Although reports of human disease associated with STEC are scarce in Brazil, the colonization of the animal reservoir by potentially pathogenic strains offers a significant risk to our population.
AIM: The occurrence of virulence markers, serotypes and invasive ability were investigated in Shiga toxin-producing Escherichia coli (STEC) isolated from faecal samples of healthy dairy cattle at Rio de Janeiro State, Brazil. METHODS AND RESULTS: From 1562 stx-positive faecal samples, 105 STEC strains were isolated by immuno-magnetic separation (IMS) or plating onto MacConkey agar (MC) followed by colony hybridisation. Fifty (47·6%) strains belonged to nine serotypes (O8:H19, O22:H8, O22:H16, O74:H42, O113:H21, O141:H21, O157:H7, O171:H2 and ONT:H21). The prevalent serotypes were O157:H7 (12·4%), O113:H21 (6·7%) and O8:H19 (5·7%). Virulence genes were identified by polymerase chain reaction (PCR). E-hlyA (77·1%) was the more prevalent virulence marker, followed by espP (64·8%), saa (39%), eae (24·8%) and astA (21·9%). All O157:H7 strains carried the γ (gamma) variant of the locus of enterocyte effacement (LEE) genes and the stx2c gene, while the stx1/stx2 genotype prevailed among the eae-negative strains. None of the eae-positive STEC produced the localized adherence (LA) phenotype in HEp-2 or Caco-2 cells. However, intimate attachment (judged by the fluorescent actin staining test) was detected in some eae-positive strains, both in HEp-2 (23·1%) and in Caco-2 cells (11·5%). Most strains (87·5%) showed 'peripheral association' (PA) adherence phenotype to undifferentiated Caco-2 cells. Twenty-five (92·6%) of 27 strains invaded Caco-2 cells. The highest average value of invasion (9·6%) was observed among the eae-negative bovine strains from serotypes described in human disease. CONCLUSION: Healthy dairy cattle is a reservoir of STEC carrying virulence genes and properties associated with human disease. SIGNIFICANCE AND IMPACT OF THE STUDY: Although reports of human disease associated with STEC are scarce in Brazil, the colonization of the animal reservoir by potentially pathogenic strains offers a significant risk to our population.
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