Micrograph depicting Gram-positive C. diff bacteria using a .1µm filter.
Public Domain : Obtained from CDC image library (http://phil.cdc.gov)
Clostridium Difficile
Clostridium difficile (C. diff) is a gram- positive bacterium that lives naturally in the gut. In healthy individuals, the levels of C. diff are kept constant as it is outcompeted by other species in the gut flora. However, when patients receive large doses of antibiotics, competing gut flora can be wiped out. This can allow numbers of C. diff to increase to a level where infection can be caused, resulting in severe colitis. C. diff has therefore become a major cause of hospital acquired infections, with, for example, some 2645 patients in hospitals in England and Wales found suffering from C. diff induced colitis in March- May 2010. Infection rates have also been high at Dundee's Ninewells Hospital, which is affiliated with the University of Dundee, and so for us, this is also a very local health problem. Up until now, there have been two ways of treating this problem: prescribe more antibiotics, with the added difficulty of possibly causing more resistance to build-up, or by means of faecal transplant. A faecal transplant involved the faeces of another person being transplanted directly into the patient's colon or through a drip into the stomach. This has been proven to be effective in test cases, but is obviously an unsavoury form of treatment for many patients and so the idea of creating an alternative gave rise to this project.
Type VI Secretion System
Many bacterial species have evolved secretion systems Type VI secretion systems are naturally found in gram negative organisms, including Serratia species, Vibrio cholerae and Pseudomonas aeruginosa, but a putative type VI system has also been found in Salmonella typhimurium, which is closely related to Escherichia coli (E. coli). The proteins for Salmonella type VI secretion systems are encoded by more than 13 genes, including Hcp, which encodes for the main feature of the system, the needle. This projects through the periplasm and outer membrane, secreting effector molecules, via the tip protein which is encoded by the gene VgrG. Hcp and VgrG are largely conserved across all species expressing these systems. The secreted effector molecules are thought to play a role in the pathogenesis of higher organisms and could help facilitate interactions with other bacteria.
Micrograph depicting Gram-positive C. diff bacteria using a .1µm filter.
Public Domain : Obtained from CDC image library (http://phil.cdc.gov)
Micrograph depicting Gram-positive C. diff bacteria using a .1µm filter.
Public Domain : Obtained from CDC image library (http://phil.cdc.gov)
Project Summary
The aim of our project is to create a new type of synthetic E. coli, expressing a simplified type VI secretion system that will secrete a C. diff specific effector, endolysin. It is hoped that the needle will either be able to puncture the C. diff cells and secrete the endolysin directly into the organism or that the endolysin will come into contact with the C. diff cell surface after secretion. We hope to prove that the new strain of E. coli will be able to produce enough needles on the cell surface which can then come into contact with C. diff cells and that enough endolysin is secreted to kill them, so in vitro experiments will be carried out to test this hypothesis. Experiments will also be set up that show that our strain of E. coli is able to out-compete C. diff, resulting in reduced numbers of the bacterium and so less chance of infection. A big part of the project will include the modelling of these processes.
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