Genetic Characterization of Escherichia coli O157:H7/- Strains Carrying the stx2 Gene but Not Producing Shiga Toxin 2

Nine Escherichia coli O157:H7/– strains isolated primarily from non‐clinical sources in Thailand and Japan carried the stx2 gene but did not produce Stx2 toxin in a reversed passive latex agglutination (RPLA) assay. A strain (EDL933) bearing a stx2 phage (933W) was compared to a strain (Thai‐12) tha...

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Bibliographic Details
Published in:Microbiology and immunology 2006, Vol.50 (2), p.135-148
Main Authors: Koitabashi, Tsutomu, Vuddhakul, Varaporn, Radu, Son, Morigaki, Tadaaki, Asai, Norio, Nakaguchi, Yoshitsugu, Nishibuchi, Mitsuaki
Format: Article
Language:English
Subjects:
Animals
Bacteriophage lambda - genetics
Base Sequence
Cattle
Cloning, Molecular
DNA, Bacterial - chemistry
DNA, Bacterial - genetics
Electrophoresis, Gel, Pulsed-Field
Escherichia coli Infections - microbiology
escherichia coli O157
Escherichia coli O157 - genetics
Escherichia coli O157 - metabolism
Food Microbiology
Humans
lambdoid phage
Latex Fixation Tests
Polymerase Chain Reaction
Promoter Regions, Genetic
Sequence Alignment
Sequence Homology, Nucleic Acid
shiga toxin
Shiga Toxin 2 - biosynthesis
Shiga Toxin 2 - genetics
Shiga Toxin 2 - metabolism
Viral Proteins - genetics
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Summary:Nine Escherichia coli O157:H7/– strains isolated primarily from non‐clinical sources in Thailand and Japan carried the stx2 gene but did not produce Stx2 toxin in a reversed passive latex agglutination (RPLA) assay. A strain (EDL933) bearing a stx2 phage (933W) was compared to a strain (Thai‐12) that was Stx2‐negative but contained the stx2 gene. To study the lack of Stx2 production, the Thai‐12 stx2 gene and its upstream nucleotide sequence were analyzed. The Thai‐12 stx2 coding region was intact and Stx2 was expressed from a cloned stx2 gene using a plasmid vector and detected using RPLA. A lacZ fusion analysis found the Thai‐12 stx2 promoter non‐functional. Because the stx2 gene is downstream of the late promoter in the stx2 phage genome, the antitermination activity of Q protein is essential for strong stx2 transcription. Thai‐12 had the q gene highly homologous to that of Φ21 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 stx2 phage was not observed in Stx2‐negative strains. The q‐stx2 gene sequence of Thai‐12 was well conserved in all Stx2‐negative strains. A PCR assay to detect the Thai‐12 q‐stx2 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 stx2‐positive O157 strains that produce little or no Stx2 may be widely distributed in the Asian environment.
ISSN:0385-5600
1348-0421
DOI:10.1111/j.1348-0421.2006.tb03779.x