Analysis of the role of fimbriae in the virulence of Salmonella enterica in poultry

[摘要] Salmonella is a Gram-negative bacterium that consists of two species; S. enterica andS. bongori. The species S. enterica can be further divided into 6 subspecies andsubspecies I is predominantly associated with disease in warm blooded animals andcontains over 2,500 antigenically distinct serovars. Each serovar is >90% identical atthe DNA level but can infect a different range of hosts and cause different diseases.Poultry are an important reservoir of entry of Salmonella into the human food chainowing to the contamination of their eggs and meat. The molecular mechanismsunderlying colonisation of food producing animals with Salmonella are unknown.Fimbrial genes encode proteinaceous surface exposed appendages which have beenshown to mediate adhesion of bacterial cells but the precise role for fimbriae in thecarriage and virulence of Salmonella is poorly defined.The purpose of this study was to annotate and characterise the fimbrial genes of thepoultry-associated S. enterica serovars Enteritidis and Gallinarum and relate this role tohost-specificity. The availability of the genome sequences of several strains of S.enterica allowed a comparison of the sequence, location and repertoire of fimbrial genesand although no unique fimbrial genes were identified all serovars possessed a uniquerepertoire. The host-specific serovars contain a higher number of pseudogenes withinfimbrial operons than the ubiquitous serovars and the rate of attrition of fimbrial geneswas 3-4 fold higher than the genomic mean. Such gene decay may partially explain thenarrowing of host-range of the host-restricted and host-specific serovars.Polymorphisms that may alter transcription were identified along with targets that maybe associated with phase variation of the fimbrial genes.Lambda red-mediated homologous recombination was used to construct a panel of S.Enteritidis P125109 and S. Gallinarum 287/91 strains lacking major fimbrial subunit genes which were examined in vitro and in vivo. Several fimbrial subunits played a rolein the adherence to and invasion of different cell lines in different growth conditions andthe role appeared to be serovar-specific. A mutation in the steA gene impairedinteractions with different cell lines in vitro but this phenotype was found to be due to apolar effect on genes downstream of steA. The majority of fimbrial subunits played nosignificant role in the colonisation of the alimentary tract in an established chickenmodel. Mutation of the stcA gene resulted in the greatest degree of attenuation in vivoof all of the fimbrial mutants examined. This phenotype was trans-complemented andwas not the result of a polar or second-site defect thereby fulfilling molecular Koch’spostulates. The stcA genes therefore play a significant role in the colonisation of thechicken caeca.

[发布机构] University:University of Glasgow;Department:School of Veterinary Medicine

[关键词] SF600 Veterinary Medicine