title: Quantitative Tracking ofSalmonellaEnteritidis Transmission Routes Using Barcode-Tagged Isogenic Strains in Chickens: Proof-of-Concept Study.
abstract: Salmonellais an important foodborne bacterial pathogen, however, a fundamental understanding onSalmonellatransmission routes within a poultry flock remains unclear. In this study, a series of barcode-tagged strains were constructed by inserting six random nucleotides into a functionally neutral region on the chromosome ofS. Enteritidis as a tool for quantitative tracking ofSalmonellatransmission in chickens. Six distinct barcode-tagged strains were used for infection or contamination at either low dose (103CFUs; three strains) or high dose (105CFUs; three strains) in three independent experiments (Experiment 1 oral gavage; Experiment 2 contaminated feed; Experiment 3 contaminated water). For all chick experiments, cecal and foot-wash samples were collected from a subset of the chickens at days 7 or/and 14, from which genomic DNA was extracted and used to amplify the barcode regions. After the resulting PCR amplicons were pooled and analyzed by MiSeq sequencing, a total of approximately 1.5 million reads containing the barcode sequences were analyzed to determine the relative frequency of every barcode-tagged strain in each sample. In Experiment 1, the high dose of oral infection was correlated with greater dominance of the strains in the ceca of the respective seeder chickens and also in the contact chickens yet at lesser degrees. When chicks were exposed to contaminated feed (Experiment 2) or water (Experiment 3), there were no clear patterns of the barcode-tagged strains in relation to the dosage, except that the strains introduced at low dose required a longer time to colonize the ceca with contaminated feed. Most foot-wash samples contained only one to three strains for the majority of the samples, suggesting potential existence of an unknown mechanism(s) for strain exclusion. These results demonstrated the proof of concept of using barcode tagged to investigate transmission dynamics ofSalmonellain chickens in a quantitative manner.
authors.affiliation: Department of Poultry Science, University of Arkansas , Fayetteville, AR , USA.
authors.forename: Yichao
authors.initials: Y
authors.lastname: Yang
authors.affiliation: Cell and Molecular Biology Program, University of Arkansas, Fayetteville, AR, USA; Department of Food Science, University of Arkansas, Fayetteville, AR, USA; Center of Food Safety, University of Arkansas, Fayetteville, AR, USA.
authors.forename: Steven C
authors.initials: SC
authors.lastname: Ricke
authors.affiliation: Department of Poultry Science, University of Arkansas , Fayetteville, AR , USA.
authors.forename: Guillermo
authors.initials: G
authors.lastname: Tellez
authors.affiliation: Department of Poultry Science, University of Arkansas, Fayetteville, AR, USA; Cell and Molecular Biology Program, University of Arkansas, Fayetteville, AR, USA; Center of Food Safety, University of Arkansas, Fayetteville, AR, USA.
authors.forename: Young Min
authors.initials: YM
authors.lastname: Kwon
keywords: Salmonella Enteritidis; barcode-tagged isogenic strains; chickens; quantitative tracking; transmission