Highly conserved B-subunit genes of Shiga-like toxin II variants found in Escherichia coli O157 strains.
To determine the degree of heterogeneity among Shiga-like toxin-II (SLT-II)-related toxins present in enterohemorrhagic Escherichia coli O157 strains, slt-IIB-related genes of 15 strains were amplified and sequenced. Of these 15 isolates, six contained only the slt-II-related genes, seven strains harbored slt-II-related genes together with slt-II, and two strains had slt-II-related genes plus slt-I. In strains carrying slt-II-related genes alone or in combination with slt-I, the PCR fragments were directly subjected to Taq cycle sequence analysis. Direct sequencing was not possible with the seven strains possessing both slt-II and slt-II-related genes, since the PCR products contained both genes. In order to allow sequence analysis of these slt-II-related genes, the PCR products were first subjected to restriction enzyme digestion with FokI, which selectively digested slt-IIB. This resulted in an undigested 270-bp fragment consisting of pure slt-II-related genes. Interestingly, comparison of the nucleotide sequences revealed 100% homology of all analyzed 15 slt-IIB-related toxin genes. In addition, the nucleotide sequence of slt-IIB-related toxin genes were identical to slt-IIcB. Our findings indicate that SLT-IIc is a major variant form of SLT-II present in E. coli O157 strains.
Institut für Hygiene und Mikrobiologie, Universität Würzburg, FRG.
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Rüssmann
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Schmidt
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Caprioli
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Karch
D001427:Bacterial Toxins / Q000235:genetics*; D001483:Base Sequence; D003092:Colitis / Q000382:microbiology; D017124:Conserved Sequence; D004926:Escherichia coli / Q000235:genetics* / Q000472:pathogenicity; D005798:Genes, Bacterial / Q000235:genetics*; D014644:Genetic Variation; D006470:Hemorrhage / Q000382:microbiology; D006801:Humans; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D011487:Protein Conformation; D022641:Shiga Toxin 2; D014774:Virulence
D001427:Bacterial Toxins; D022641:Shiga Toxin 2