Genetic characterization of Escherichia coli O157: H7/- strains carrying the stx2 gene but not producing Shiga toxin 2.
Microbiol Immunol
; 50(2): 135-48, 2006.
Article
em En
| MEDLINE
| ID: mdl-16490932
ABSTRACT
Nine Escherichia coli O157 H7/- strains isolated primarily from non-clinical sources in Thailand and Japan carried the stx(2) gene but did not produce Stx2 toxin in a reversed passive latex agglutination (RPLA) assay. A strain (EDL933) bearing a stx(2) phage (933W) was compared to a strain (Thai-12) that was Stx2-negative but contained the stx(2) gene. To study the lack of Stx2 production, the Thai-12 stx(2) gene and its upstream nucleotide sequence were analyzed. The Thai-12 stx(2) coding region was intact and Stx2 was expressed from a cloned stx(2) gene using a plasmid vector and detected using RPLA. A lacZ fusion analysis found the Thai-12 stx(2) promoter non-functional. Because the stx(2) gene is downstream of the late promoter in the stx(2) phage genome, the antitermination activity of Q protein is essential for strong stx(2) transcription. Thai-12 had the q gene highly homologous to that of Phi21 phage but not to the 933W phage. High-level expression of exogenous q genes demonstrated Q antitermination activity was weak in Thai-12. Replication of stx(2) phage was not observed in Stx2-negative strains. The q-stx(2) gene sequence of Thai-12 was well conserved in all Stx2-negative strains. A PCR assay to detect the Thai-12 q-stx(2) sequence demonstrated that 30% of O157 strains from marketed Malaysian beef carried this sequence and they produced little or no Stx2. These results suggest that stx(2)-positive O157 strains that produce little or no Stx2 may be widely distributed in the Asian environment.
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Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Escherichia coli O157
/
Toxina Shiga II
/
Infecções por Escherichia coli
Limite:
Animals
/
Humans
Idioma:
En
Revista:
Microbiol Immunol
Ano de publicação:
2006
Tipo de documento:
Article
País de afiliação:
Japão