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Bacterial and host genes in Salmonella colonisation in poultry - OZ0320

Description
Poultry remain the major source of Salmonella for man. Carcass contamination arises largely from the ability of food-poisoning serotypes of Salmonella to colonise the alimentary tract of poultry in the absence of disease. Egg infection can also result from surface contamination of the egg during passage through the cloaca of the infected bird. Elucidation of the microbiological and molecular basis of intestinal colonisation by Salmonella will underpin the development of biological control measures. Such measures will become increasingly important with (a) the economic constraints of upgrading housing and (b) the costs of improving feed and management quality and (c) problems associated with the use of antibiotics.
This project seeks to provide information on the major bacterial and host factors which determine colonisation, knowledge of which might be used in the design of non-pharmaceutical, biological control measures. It also seeks to gain a further understanding of the mechanism of genus-specific exclusion of colonisation (in which one Salmonella strain may inhibit another in vivo) which may be used to enhance non-immune resistance in the chick intestine.
The major aim of the project is to identify the mechanisms used by Salmonella strains in the intestine to obtain their energy, from major carbon sources and through selected electron acceptors other than oxygen.. There is evidence that most growth of Salmonella occurs at the boundary of the mucosa and the contents since Salmonella organisms are under starvation stress in the lumen where they are greatly outnumbered by other bacteria. We also have evidence that the mucus layer is an important carbon source for colonising Salmonella. Catabolism of these compounds in the gut does not involve oxygen as electron acceptor and it is likely that others are used in this anaerobic environment. Identification of the genes required for major carbon source utilisation and electron acceptor usage and incorporation of these mutated genes into live vaccines would induce a non-colonising vaccine phenotype which would be shed in the faeces of vaccinated birds for a shorter period than the live vaccines currently available and thus not be present in birds sent to slaughter.
Colonisation of the alimentary tract of the newly hatched chicken by Salmonella results in massive multiplication and faecal shedding. This may be largely prevented by pre-inoculation with an avirulent Salmonella strain. This multiplies and excludes other strains within a matter of hours, by a purely microbiological phenomenon. This genus-specific inhibition of colonisation (a novel, genus-specific form of competitive exclusion) was originally identified and has been investigated extensively at IAH, Compton and modelled in vitro using stationary-phase nutrient broth cultures. One of the central controlling mechanisms relating to growth in vitro and in the intestine is the rate of initiation of chromosomal replication. It is likely that one component of this is quorum sensing, which is the ability of a bacterial culture to sense itself when the cells are present at high density by the constitutive production of a signalling molecule. The identification of products in stationary-phase broth cultures which regulate this will allow the possibility of oral administration of products to reduce bacterial growth rates in the intestine. The practical consequence is that live attenuated vaccines could be administered orally to newly hatched chicks such that exclusion occurs in the gut. The vaccine strain would persist long enough to induce immunity in the usual way. A combination of this characteristic and the non-colonising trait described above should lead to the development of vaccines which will fulfil the necessary criteria for live enteric vaccines, which include the requirement that vaccine strains should not enter the human food chain.
We have identified differences in colonisation ability in different inbred lines of chickens housed at the IAH. The increased resistance seen in some lines is inherited as a dominant trait and is not related to sex, MHC (major histocompatibility complex), NRAMP1 (the ity gene responsible for resistance in some mouse breeds) or SAL1 (the major chicken gene identified at IAH, Compton, responsible for resistance to systemic salmonellosis). We will begin to identify the biological basis of this. A major possibility is a quantitative and/or qualitative difference in the alpha- and beta-defensins and the mucus produced by the mucosa. We will explore the synergy between the inhibition of colonisation as a result of this genetic component and the use of killed vaccines to control intestinal colonisation and faecal shedding. Incorporation of this genotype into commercial birds by a natural breeding programme should increase resistance to infection and thus reduce colonisation if applied to commercial poultry flocks.



Objective

1. To determine the contribution of components of the biosynthetic pathway to sialic acid in the carbon metabolism of Salmonella serotypes that are able to colonise the alimentary tract of chickens.
2. To determine the contribution of selected electron acceptors in the intestine of chickens to bacterial respiration in Salmonella during colonisation.
3. To determine the role of regulation of initiation of DNA replication in stationary-phase growth-suppression and genus-specific inhibition of intestinal colonisation.
4. To determine whether differences occur in the expression or activity of intestinal defensins in inbred lines of chickens that differ in their susceptibility to intestinal salmonellosis.
5. To evaluate whether mucin obtained from the intestines of different inbred lines of birds is able to act as a nutrient for colonising Salmonella serotypes.
Project Documents
• Final Report : Bacterial and host genes in Salmonella colonisation in poultry   (611k)
• Final Report : Bacterial and host genes in Salmonella colonisation in poultry   (611k)
Time-Scale and Cost
From: 2002

To: 2005

Cost: £956,279
Contractor / Funded Organisations
Institute for Animal Health (BBSRC)
Keywords
Animal Health              
Biotechnology              
GM Non-Food              
Plants and Animals              
Salmonella              
Transmission              
Zoonoses              
Fields of Study
Animal Health