title: Use of ramification amplification assay for detection of Escherichia coli O157:H7 and other E. coli Shiga toxin-producing strains.
abstract: Escherichia coli O157:H7 and other Shiga toxin-producing E. coli (STEC) strains are important human pathogens that are mainly transmitted through the food chain. These pathogens have a low infectious dose and may cause life-threatening illnesses. However, detection of this microorganism in contaminated food or a patient's stool specimens presents a diagnostic challenge because of the low copy number in the sample. Often, a more sensitive nucleic acid amplification method, such as PCR, is required for rapid detection of this microorganism. Ramification amplification (RAM) is a recently introduced isothermal DNA amplification technique that utilizes a circular probe for target detection and achieves exponential amplification through the mechanism of primer extension, strand displacement, and ramification. In this study, we synthesized a circular probe specific for the Shiga toxin 2 gene (stx(2)). Our results showed that as few as 10 copies of stx(2) could be detected, indicating that the RAM assay was as sensitive as conventional PCR. We further tested 33 isolates of E coli O157:H7, STEC, Shigella dysenteriae, and nonpathogenic E. coli by RAM assay. Results showed that all 27 STEC isolates containing the stx(2) gene were identified by RAM assay, while S. dysenteriae and nonpathogenic E. coli isolates were undetected. The RAM results were 100% in concordance with those of PCR. Because of its simplicity and isothermal amplification, the RAM assay could be a useful method for detecting STEC in food and human specimens.
authors.affiliation: Molecular Pathology Laboratory, Mount Sinai School of Medicine, Box 1122, One Gustave Levy Place, Box 1122, New York, NY 10029, USA.
authors.forename: Fan
authors.initials: F
authors.lastname: Li
authors.forename: Chunyan
authors.initials: C
authors.lastname: Zhao
authors.forename: Wandi
authors.initials: W
authors.lastname: Zhang
authors.forename: Shenghui
authors.initials: S
authors.lastname: Cui
authors.forename: Jianghong
authors.initials: J
authors.lastname: Meng
authors.forename: Josephine
authors.initials: J
authors.lastname: Wu
authors.forename: David Y
authors.initials: DY
authors.lastname: Zhang
mesh_terms: D000818:Animals; D002417:Cattle; D015342:DNA Probes; D004926:Escherichia coli / Q000302:isolation & purification* / Q000378:metabolism / Q000472:pathogenicity; D004927:Escherichia coli Infections / Q000382:microbiology; D019453:Escherichia coli O157 / Q000302:isolation & purification* / Q000378:metabolism / Q000472:pathogenicity; D006801:Humans; D008460:Meat / Q000382:microbiology; D021141:Nucleic Acid Amplification Techniques / Q000379:methods*; D016133:Polymerase Chain Reaction; D012680:Sensitivity and Specificity; D022641:Shiga Toxin 2 / Q000096:biosynthesis* / Q000235:genetics*
chemical_list: D015342:DNA Probes; D022641:Shiga Toxin 2