Identification of avian pathogenic Escherichia coli genes required for carriage and virulence in poultry

点击翻译按钮获取中文摘要

Escherichia coli is typically a harmless inhabitant of intestines of animals and humans. However, some E. coli strains possess traits that equip them with the potential to cause disease. Pathogenic E. coli are a major cause of diarrhoeal disease world-wide, but some strains can cause extra-intestinal disorders such as urinary tract infections, septicaemia and meningitis. The bacterial factors that enable E. coli to cross mucosal barriers and persist at systemic sites are poorly understood. One such group of extra-intestinal pathogens comprises avian pathogenic E. coli (APEC), which cause severe systemic disease in birds. APEC are a major economic and welfare problem for the poultry industry world-wide. APEC affect birds of all ages and cause colibacillosis which can result in sudden death, reduced egg hatching and condemnation of carcasses at slaughter. Whilst birds may be prediposed to colibacillosis by viral infection, stress and environmental factors, it is widely agreed that the problem could be alleviated by targeting APEC. However, the bacterial factors that influence the carriage and virulence of APEC in poultry are poorly understood. Furthermore, APEC isolated from poultry with colibacillosis are often unrelated and few conserved traits have been found to exist among virulent isolates. Antibiotic treatment is complicated by the lack of signs of disease prior to death and concern about the evolution and spread of new antibiotic resistances. Whilst vaccines against APEC have been developed, these are of limited value since they protect birds only against the strain from which they were derived. There is a pressing need to develop broadly cross-protective APEC vaccines. We believe that by dissecting the mechanisms by which APEC colonise the respiratory tract of poultry and spread to systemic sites we can identify bacterial factors that may be suitable for inclusion into a vaccine. For such vaccines to be effective against all APEC, it will be necessary to confirm that the factors are present in a wide variety of field APEC isolates. We propose to employ a technique called signature-tagged transposon mutagenesis (STM) to identify APEC factors required for the induction of colibacillosis in turkeys. STM makes it possible to track the fate of uniquely tagged bacterial mutants during their interaction with the host. The composition of a pool of mutants recovered from inoculated birds can be compared to the composition of the inoculum and in this way, mutants unable to survive in the host identified (Part 1. Fig. 1). The factors disrupted in such weakened mutants can then be identified. We have successfully used STM to identify genes of Salmonella and E. coli O157 required for colonisation of farm animals. With the information gleaned from such studies, we have then sought to develop vaccines for the control of these agents. In recognition of the value of the proposed studies to the poultry industry the British Poultry Council and Aviagen Turkeys (formerly British United Turkeys Ltd) have agreed to support the project in cash and in kind, respectively. The aims of the project are: 1. To identify factors that enable APEC to colonise the respiratory tract of turkeys and spread to other organs. 2. To confirm that such factors are found in a wide variety of field APEC isolates. 3. To confirm that such factors play an important role in disease by disrupting them and characterising the mutant strains in turkeys. The reasons for the loss of virulence will then be assessed in a number of laboratory-based experiments. 4. To determine whether purified APEC virulence factors can induce protection against APEC infection.