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Detection of a non-toxic derivative of the heat labile toxin produced by enteroxigenic Escherichia coli strains isolated from a human subject in Brazil

M. Ang-Simões B. E. C Guth; Luís Carlos de Souza Ferreira; Congresso Brasileiro de Microbiologia (22. 2003 Florianópolis)

Sociedade Brasileira de Microbiologia, 2003

Sociedade Brasileira de Microbiologia 2003

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  • Título:
    Detection of a non-toxic derivative of the heat labile toxin produced by enteroxigenic Escherichia coli strains isolated from a human subject in Brazil
  • Autor: M. Ang-Simões
  • B. E. C Guth; Luís Carlos de Souza Ferreira; Congresso Brasileiro de Microbiologia (22. 2003 Florianópolis)
  • Assuntos: MICROBIOLOGIA
  • É parte de: Sociedade Brasileira de Microbiologia, 2003
  • Notas: Disponível em CD-Rom
  • Descrição: Enterotoxigenic Escherichia coli (ETEC) strains represent important etiological agents of diarrhea in developing countries and characteristically produce at least one of two enterotoxins: heat-labile toxin (LT) and heat stable toxin (ST). LT, an AB type toxin, is composed of one toxic portion (A subunit encoded by the extA gene), and five receptor binding subunits (B subunit encoded by the extB gene) and is endowed with both adjuvant and anti-tolerogenic effects. In this work we reported the identification of spontaneous LT mutant derivative produced by an ETEC LT/ST O78:H12 strain isolated from a diarrhoeic child in São Paulo city. The sequencing of the mutant etx genes revealed the presence of 11 point mutations: 9 at the extA gene and 2 at the extB gene with ragard to the sequence of the toxin produced by the reference ETEC H10407 strain. Seven of the detected mutations lead to chance in the amino acid sequences of the encoded proteins, 6 at the A subunit (D189N, S190L, G196D, K213E, S224T, N238D) and 1 at the B subunit (T75A). The mutant LT toxin had a reduction of 25% of the affinity to the specific GM1ganglioside receptor when compared to the standard toxin produced by the H10407 strain. Moreover, toxicity assays based on Vero cells demonstrated that the mutant LT is devoid of any in vitro toxic effects up to concentrations of 1,000 ng/mL while the wild type LT were toxic to Vero cells at concentration of 3.75 ng/ml. Based on the results obtained with other mutant
    LT toxins, three mutations leading to amino acid changes were probably ascribed to the lack of toxic effects of the mutant LT (S190L, G196D, and S224T). The ability to produce the mutant LT by the isolated ETEC expression ranged from 2.5 to 14 mg/L according to growth conditions. The present results indicate that non toxic LT derivatives can be found among ETEC strains isolated from human subjects and may represent useful tools for studies on LT biological activities and development
  • Editor: Sociedade Brasileira de Microbiologia
  • Data de criação/publicação: 2003
  • Formato: res. MM 116.
  • Idioma: Inglês
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  • Realização: ABCD-USP USP   Logos de Redes Sociais: Freepik

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