Our Sensor

The goal of our project is to design a biosensor to rapidly identify cattle known as super shedders. Super shedders are cattle that excrete extremely large numbers of E.coli O157:H7 a subgroup of E. coli referred to as Enterohemorrhagic E. coli (EHEC). EHEC organisms produce a toxin called Shiga toxin or verotoxin. This toxin binds to renal cells and lyses them, resulting in hemolytic-uremic syndrome (HUS) in humans and can be deadly. Supershedders excrete more than 104 colony forming units of E. coli O157:H7 in every gram of their feces and can contaminate other cattle in the same holding pen as well as the meat downstream. Super-shedders are thought to be the reason for 95% of the E. coli O157:H7 contamination in the industry.

We are building a DNA-based biosensor, as it is more reliable and cheaper than a protein-based sensor; antibodies are expensive and the proteins that they target can get degraded during the sample preparation, whereas DNA is much more stable. A DNA-based sensor also enabled us to target a broader range of harmful E.coli. Our sensor is specific to shiga toxin (stx2) gene, present not only in E.coli O157:H7, but other EHEC strains as well. This means our detector will not only be specific to one specific strain of EHEC, but instead target a broad group of EHEC organisms. Click on the components below to learn more about their design and function. View our animation below to see how the system would actually work!

To see how our system would work as a platform in industry and in the registry, please click here.

The FerriTALE System:

As seen in the video above our goal is to develop a strip based assay that can alert us upon detection of pathogen specific DNA sequence, namely stx2. We will treat our sample collected from the supershedders with a TALE-Ferritin complex (a FerriTALE!). This DNA-TALE-Ferritin complex would then be flown over our strip that contains a second, immobilized TALE that recognizes yet another 18-20 bp region on the stx 2 gene. This second TALE will immobilize our DNA-TALE-ferritin complex on the strip. Following immobilization we will add substrate to our strip. Only in the presence of both the EHEC sequences we get a colour change on the strip. If there is only one of the sequences present, the colour change does not occur either due to lack of immobilization or due to lack of presence of a reporter.

System Elements

Figure 1. Our system is composed of both an immobile element on the strip that will capture our target DNA and a mobile element that will report the presence of our target DNA.