Genomic variability of O islands encoding tellurite resistance in enterohemorrhagic Escherichia coli O157:H7 isolates - PubMed (original) (raw)

Genomic variability of O islands encoding tellurite resistance in enterohemorrhagic Escherichia coli O157:H7 isolates

Diane E Taylor et al. J Bacteriol. 2002 Sep.

Abstract

Strains of Escherichia coli causing enterohemorrhagic colitis belonging to the O157:H7 lineage are reported to be highly related. Fifteen strains of E. coli O157:H7 and 1 strain of E. coli O46:H(-) (nonflagellated) were examined for the presence of potassium tellurite resistance (Te(r)). Te(r) genes comprising terABCDEF were shown previously to be part of a pathogenicity island also containing integrase, phage, and urease genes. PCR analysis, both conventional and light cycler based, demonstrated that about one-half of the Te(r) E. coli O157:H7 strains (6 of 15), including the Sakai strain, which has been sequenced, carried a single copy of the Te(r) genes. Five of the strains, including EDL933, which has also been sequenced, contained two copies. Three other O157:H7 strains and the O46:H(-) strain did not contain the Te(r) genes. In strains containing two copies, the Te(r) genes were associated with the serW and serX tRNA genes. Five O157:H7 strains resembled the O157 Sakai strain whose sequence contained one copy, close to serX, whereas in one isolate the single copy was associated with serW. There was no correlation between Te(r) and the ability to produce Shiga toxin ST1 or ST2. The Te(r) MIC for most strains, containing either one or two copies, was 1,024 micro g/ml, although for a few the MIC was intermediate, 64 to 128 micro g/ml, which could be increased to 512 micro g/ml by pregrowth of strains in subinhibitory concentrations of potassium tellurite. Reverse transcriptase PCR analysis confirmed that in most strains Te(r) was constitutive but that in the rest it was inducible and involved induction of terB and terC genes. Only the terB, -C, -D, and -E genes are required for Te(r). The considerable degree of homology between the ter genes on IncH12 plasmid R478, which originated in Serratia marcescens, and pTE53, from an E. coli clinical isolate, suggests that the pathogenicity island was acquired from a plasmid. This work demonstrates diversity among E. coli O157:H7 isolates, at least as far as the presence of Te(r) genes is concerned.

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Figures

FIG. 1.

FIG. 1.

Map of OI 43 and 48 from E. coli O157: H7 strain EDL933 (14). Genes of interest encode urease, a ribosomal protein, tellurite resistance, an insertion sequence, and adhesin (iha). A putative ribosomal protein gene (unlabeled) downstream of the urease operon is 96% identical to E. coli K-12 ORF ygkM. The overall size of the islands is 87,562 bp. The region from bp 20500 to 50000 is shown.

FIG. 2.

FIG. 2.

Comparison of Ter determinants from various sources. Deduced ORFs are shown, with the sizes in amino acids of the products of ORFs from E. coli O157:H7 EDL933 (14) below the filled arrows. ORFs from Serratia marcescens plasmid R478 (24) are most closely related. The percent identity of each ORF to its corresponding ORF in EDL933 is shown below. Those labeled TlpD and TlrC, -B, and -A from E. coli O157: H7 strain 86-24NalR were given this nomenclature by Tarr et al. (19). Plasmid pMJ606 contains the cloned Ter determinants from pMER610 originally isolated from an Alcaligenes sp. (7). Plasmid pTE53 originated in a clinical isolate of E. coli (3). The last two sequences are from Proteus sp. and D. radiodurans genome sequence databases.

FIG. 3.

FIG. 3.

PFGE of E. coli O157:H7 DNA digested with _Xba_I. The strain numbers are shown at the top of the gel. Lambda phage size markers were run at each end of the gel and in the central well.

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