Award details

A novel bacterial defence system against antimicrobial peptides: Implications for host colonisation in the foodborne pathogen Campylobacter jejuni

Reference	BB/K005642/1
Principal Investigator / Supervisor	Professor Mark Stevens
Co-Investigators / Co-Supervisors
Institution	University of Edinburgh
Department	The Roslin Institute
Funding type	Research
Value (£)	105,169
Status	Completed
Type	Research Grant
Start date	11/12/2013
End date	10/12/2016
Duration	36 months

Abstract

Research on the molecular basis of colonisation by Campylobacter jejuni of the chicken host is required to inform the rational design of strategies to eradicate this pathogen from poultry flocks. It is not clear, however, how C. jejuni evades avian innate immunity, particularly that mediated by cationic antimicrobial peptides (CAMPs). Many strains of C. jejuni are known to be naturally resistant to these molecules but the genetic and structural basis for this has not, up to now, been adequately explained. We have discovered an entirely novel, previously unrecognized, multi-component defence system in C. jejuni that can explain high-level CAMP resistance, which we believe is likely to be necessary for successful host colonisation. This system consists of a membrane bound sensor protein and a small DNA binding protein which control the expression of three genes encoding an inner membrane protein, an outer membrane anchored lipoprotein and a periplasmic protein, as well as certain dsb genes and genes involved in peptide transport and metabolism. We have solved the structure of the lipoprotein, shown that it binds the model CAMP polymyxin B and that a cognate null mutant is highly sensitive to polymyxin B killing. Our aim is to determine the function of each of the components of this complex system and their contribution to chicken colonisation. This will be achieved by investigating the mechanism of action of the lipoprotein and determining if it provides resistance to structurally diverse CAMPs; determining the roles of the uncharacterised genes by mutant studies; determining what the role of the Dsb system is in CAMP resistance; investigating the connection between peptide transport and CAMP transport and degradation; and determining the importance of this system in vivo by chicken colonisation studies with selected mutants. We believe this work could provide new avenues for intervention and will impact on future eradication programmes for C. jejuni in chickens.

Summary

Some bacteria get into the food that we eat and cause food-poisoning. Some of these bacteria are quite common but are usually killed during cooking. When chicken meat is not cooked properly, one of these types of bacteria, called Campylobacter jejuni, is a particular problem. It normally lives harmlessly in the intestines of chickens but in humans causes severe diarrohea, which although not usually life-threatening, causes considerable impacts on time off work and in some cases can lead to serious complications. By understanding in detail the way in which this bacterium interacts with both its chicken and human hosts, we may be able to stop colonisation, prevent infection or design better treatments. We have discovered a previously unsuspected way in which this bacterium stops itself being killed by molecules normally produced by the host, called antimicrobial peptides. These molecules try to insert themselves into the membrane of the bacteria to create a pore, through which the bacterial contents leak out, causing death. But C. jejuni can sense the presence of these peptides, and in response deploys a protein at its surface which we have shown can bind them and stop them getting to the cell membrane, which therefore makes the bacteria highly resistant to their action. In this research, we wish to understand the details of how the bacteria sense and respond to these peptides, how the binding protein works and the role of some other proteins that are controlled by this system. The results should allow us to get a better knowledge of the way in which the bacterium uses this novel defence system in the colonisation process and to identify vulnerabilities, which could be exploited in future to limit its growth in chickens and to treat human infections.

Impact Summary

Please see Impact Summary submitted by lead applicant (joint ref. N1617101).

Committee	Research Committee B (Plants, microbes, food & sustainability)
Research Topics	Animal Health, Microbial Food Safety, Microbiology, Structural Biology
Research Priority	X – Research Priority information not available
Research Initiative	X - not in an Initiative
Funding Scheme	X – not Funded via a specific Funding Scheme

Associated awards:

BB/K005510/1 A novel bacterial defence system against antimicrobial peptides: Implications for host colonisation in the food-borne pathogen Campylobacter jejuni

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