Team:Dundee/Project

Clostridium difficile is a gram-positive bacterium that lives naturally in the gut of some people. In healthy individuals, the levels of C. difficile are kept constant due to competition with other naturally occurring bacterial species in the gut flora. However, when patients receive large doses of broad spectrum antibiotics, microbiome species of the gut can become depleted or wiped out. In the absence of natural competition, the population of C. difficile is free to increase to an infectious level. C. difficile infections can cause diarrhoea, bloating, severe abdominal pain and in some cases severe pseudomembranous colitis. It can be fatal in the elderly and those suffering from severe health conditions. What makes C. difficile a serious issue for hospitals is that spores can be released into the environment leading to transmission of the infection between patients. C. difficile has therefore become a major cause of hospital acquired infections with 2645 patients in hospitals in England and Wales found to be suffering from C. difficile induced colitis in March-May 2010. In January this year a ward was closed at the main hospital serving the Highlands of Scotland due to 7 confirmed C. difficile infections. Ward closure was essential to allow specialist cleaning and to prevent transmission of the infection to newly admitted patients. Infection rates have also been high at Dundee's Ninewells Hospital, which is affiliated with the University of Dundee. In 2010 a ward at the hospital was closed following the deaths of 5 elderly patients due to C. difficile infections. So for our team, this is a very local and current health problem.

Current Treatment

The main form of treatment of C. difficile infections is to use antibiotics. The current drug of choice is Metronidazole but Vancomycin is also used. Evidence of resistance to Metronidazole has begun to emerge amongst C. difficile populations and in these cases Vancomycin can be used. This antibiotic is still widely accepted as a drug of last resort so is not an ideal treatment. The main issue associated with the use of antibiotics is that they are often the source of the problem. Broad spectrum antibiotics that are used to treat C. difficile infections further disrupt the gut microbiome and therefore the natural gut flora can take longer to return to their natural levels. As a result, when patients are treated with antibiotics, recurrence occurs in about 20% of cases. These cases are usually further treated by altering the antibiotics used. Following this treatment however, subsequent recurrences occur in between 40-60% of cases1. These incidents of recurrence probably occur due to the C. difficile populations recovering before the organisms that out compete them under normal circumstances can efficiently recolonize.

The second form of C. difficile infection treatment is by a faecal transplant. This method is only used in severe cases with multiple recurrences. A faecal transplant involves the faeces of a person, usually a relative of the patient, being transplanted into the patient's colon through a nasal-gastric tube in the form of a faecal slurry or via the rectum. This method aims to reintroduce the natural bacteria that are present in the colon and allow them to out compete C. difficile and keep the population at a controlled level, i.e. preventing it causing infection, as in a healthy individual. In some ways, this treatment works in an opposite way to antibiotics by encouraging the growth of the natural bacteria instead of preventing growth. This method of treatment has been shown to be successful in 95% of cases and is also highly effective in preventing recurrence. However, despite the evidence that this method of treatment is superior to antibiotics it is not widely used. The main reason for this is the obvious hygiene issues associated with handling faeces in a hospital environment.

Our Project

With all this information in mind we set out to find a possible alternative treatment for C. difficile infections using synthetic biology. We were keen to utilise the principle of the faecal transplant, i.e. allowing the natural gut bacteria to combat the C. difficile. We decided to use the common lab model organism and microbiome bacteria Escherichia coli (E. coli). Our aim was to engineer a harmless strain of E. coli to target and kill C. difficile organisms during an infection. How we did this is explained in Our Solution.