Phenotypic and molecular analysis of tellurite resistance among enterohemorrhagic Escherichia coli O157:H7 and sorbitol-fermenting O157:NM clinical isolates

Abstract

A total of 66 (98.5%) of 67 enterohemorrhagic Escherichia coli (EHEC) O157:H7 strains had increased potassium tellurite (Te) MICs (32 to 1,024 microg/ml), grew on Te-containing media, and possessed Te resistance (ter) genes, whereas 83 (96.5%) of 86 sorbitol-fermenting (SF) EHEC O157:NM strains had Te MICs of </=4 microg/ml, did not grow on Te-containing media, and lacked ter genes. Optimal detection of SF EHEC O157:NM strains requires Te-independent strategies.

FIG. 1.

Hybridization of BamHI-PstI-digested genomic DNA from EHEC O157 strains and controls with the terC probe. M, molecular weight marker (1-kb DNA ladder; Gibco-BRL). In lanes 1 to 7, the following strains are displayed (serotype, Te-MIC in micrograms per milliliter, and the presence of ter genes as detected by PCR are given in parentheses): lane 1, EDL933 (O157:H7, 128, ter⁺); lane 2, C600 (not available; <1; ter negative) (negative control); lane 3, 5288/91 (O157:H7; <1; ter negative); lane 4, 4180/97 (SF O157:NM; 256; ter negative); lane 5, 493/89 (SF O157:NM; <1; ter negative); lane 6, 3226/98 (SF O157:NM; 128; ter⁺); lane 7, 3323/98 (SF O157:NM; 128; ter⁺). Two terC copies detected in EDL933 after DNA separation by pulsed-field gel electrophoresis (19) were not distinguishable by conventional gel electrophoresis.