The March of the Superbugs

As the post-antibiotic era approaches, humanity may be forced to take a step back in modern medicine, and enter a world where antibiotics are no longer useful. The World Health Organisation has declared antibiotic resistance as “one of the biggest threats to global health." A major factor contributing to this is the misprescription of antibiotics in cases where they have no benefit, such as viral infections. With overlapping symptoms to many bacterial infections, the common cold or flu can often be misinterpreted in the short span of doctor’s appointment.

We, iGEM Sheffield, aim to address this problem by building a device that helps to slow down the development of antibiotic resistance. We are directly addressing the absence of a useful diagnostic tool in the market by building a device that can detect a bacterial infection from a sample of bodily fluid within a short time-span. Thus, we want to create a device that could prevent the unnecessary use of antibiotics.

What are we going to do?

We are engineering bacteria to fight the war against antibiotic resistance. Bacteria are engaged in a constant battle with the human body over the precious resource, iron. Iron-scavenging molecules called siderophores are released by bacteria. The immune system fights back by producing lipocalin-2, which neutralises siderophores. We are engineering a strain of E. coli to be part of a system which detects increased lipocalin-2 levels, characteristic of a bacterial infection, and responds with a change in fluorescence.

Our primary detection system involves the use of Fur, an iron-dependent repressor, linked to the fluorescent reporter protein, GFP, via a RyhB inverter. By measuring the intensity of fluorescence, the type of infection can be determined, i.e. bacterial or non-bacterial, providing evidence to produce a more informed prescription, all within your doctor’s appointment.

Selecting a Project

When brainstorming for project ideas, we approached the project from different directions to generate as many ideas as possible. For instance, we looked at current and imminent world issues, from infectious diseases to plastics recycling. We researched recent scientific developments to find synthetic biology solutions that can then be applied to problems, as well as looking at past iGEM projects to see if we could build upon those ideas. We then narrowed down the list of ideas based on whether it was feasible within the project timeframe and whether the idea was able to involve and engage all team members and their areas of expertise. Based on this shortlist, we researched and expanded on each idea in detail before voting for our favourite idea.

We decided to focus on the issue of antibiotic resistance and the lack of diagnostic tools to differentiate between bacterial and viral infections. When the cause of an infection is unknown, antibiotics are usually prescribed as a preventative measure. However, this contributes to the rise of antibiotic resistant bacteria.

Our Goal

iGEM Sheffield 2016 aims to combat the issue of a lack of diagnostic tools by building a bedside device that can discriminate between a bacterial infection and a viral infection within 15 minutes of extracting the patient’s blood sample. We plan to design Escherichia coli receptors to detect siderophores, which are molecules produced by bacteria to scavenge iron from low-iron environments such as the bloodstream. E. coli has many siderophores however we will only be focusing on the siderophore enterobactin for simplification.

Our biosensor involves the use of engineered E. coli strains that produce a detectable color change in response to the uptake of enterobactin-iron complexes. To improve the sensitivity of this system, the number of enterobactin-iron complexes being internalized by E. coli will be maximized before the actual detection step. This can be done by decoupling lipocalin-enterobactin complexes and saturating enterobactin with iron. Our detection system involves the use of the protein hemerythrin, a high-affinity iron-binding protein, that produces a colour change when bound to iron. By comparing the color against a standard, the cause of infection can be determined.

As the hemerythrin system turned out to be challenging, we established an alternative sensing system utilising antisense RNA (RhyB).

Improving a BioBrick: We have improved the function of BBa_J23100, by adding an RBS site downstream of the promoter (BBa_K2016005). Our team has also improved the characterisation of both BBa_J23100 and BBa_J23106. For more information, please visit our Parts and respective Registry pages.