Detection of Shiga Toxin-Producing Escherichia coli by in Stitu hybridization and sequence Analysis of Stx2

Kim, Eui Chong; Lee, Dong Young; Choi, Hae Shim; Joo, Se Ik; Lee, Jung Hee; Kim, Sang Hyun; Ban, Sung Hwan

Abstract

BACKGROUND: Shiga toxin-producing Escherichia coli (STEC) was found in several serotypes of E coli including 0157 serotype. Sorbitol-MacConkey agar: may be useful for the detection of E. coli 0157, but is not helpful for the detection of sorbitol-fermenting STEC other than 0157. Moreover, some strains of E. colt 0157 can ferment sorbitol. In this study, in situ hybridization using DNA probe of shiga toxin was used for the isolation of STEC from the PCR-positive stool and -Sequenbe analysis of a part of shiga toxin gene was performed.
METHODS
The stool was incubated in LB broth overnight and DNA was extracted from the culture fluid. Multiplex PCR was performed with primers for stxl and stx2 genes. Specimen showed PCR-positive was incubated on MacConkey agar and colonies were blotted with nitrocellulose membrane. Digoxigenin-labelled DNA probe for shiga toxin was made by PCR and the positive colonies were detected with anti-digoxigenin-alkaline phosphatase conjugate and nitroblue tetrazolium. Agglutination test with antisera was performed for the serotying and VTEC-RPLA kit was used for the toxin production. Sequence analysis of PCR products was performed with automatic sequence analyser.
RESULTS
An stxl-negative, but stx2-positive PCR was observed in a three-year-old girl, who visited Kumi Hospital on July 19, 1999 complaining of vomiting and diarrhea. The positive colonies were isolated by in situ hybridization using stx2-specific DNA probe. The titers of stxl and stx2 by VTEC-RPLA test were negative and 1:64, respectively. Agglutination for the serotyping was not observed with all of the 0 antisera. 160-nucleotide sequence of stx2 of this isolate was identical with bacteriophage 933W (GenBank X07865), except for the change (T-C) of 957th nucleotide and amino acid sequence was identical each other.
CONCLUSIONS
For the sensitive detection of STEC from the stool of patients with diarrhea, multiplex PCR is recommended with stxl- and stx2-specific primers. And in situ hybridization should be performed in PCR-positive specimen for the isolation of STEC. This method may be helpful for the detection of STEC as the causative microorganisms in food-borne outbreak.