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T4-03 Phenotypic and Pan-Genomic Characterisation of Salmonella enterica Serovar Uganda, an Uncommon Foodborne Pathogen

Thursday, 30 March 2017: 09:00
314-316 (The Square)
Daniel Hurley, University College Dublin, Dublin, Ireland
Maria Hoffmann, U.S. Food and Drug Administration, College Park, MD
Ellen Wall, University College Dublin, Dublin, Ireland
Eric Brown, U.S. Food and Drug Administration, College Park, MD
Marc Allard, U.S. Food and Drug Administration, College Park, MD
Salim Mattar, Universidad de Córdoba, Córdoba, Colombia
Séamus Fanning, University College Dublin, Dublin, Ireland
Introduction:  Salmonella Uganda is an uncommon serovar rarely isolated from humans. It has been implicated in only three foodborne outbreaks reported in the United States between 1993 and 2012, and little is known about its genetic diversity or pathogenicity.

Purpose: The purpose of this study was to phenotypically characterise 14 isolates and study the pan-genome of S. Uganda.

Methods:   Intracellular survival of select isolates in human THP-1 macrophages was comparatively assessed using Salmonella Typhimurium. Macrophage proinflammatory cytokine and chemokine markers were quantified, post-infection. Whole genome sequencing was performed using the Illumina MiSeq platform. A high-quality reference genome for S. Uganda CFSAN006159 was generated on the Pacific Biosciences RS II platform.

Results: In THP-1 macrophages, S. Uganda CFSAN006159 recorded a < 2 Log10 reduction between 2 and 168 hours, post infection; whereas, S. Uganda CFSAN006173 recorded a < 1 Log10 reduction over the same time course. Both S. Uganda isolates persisted for seven days within human macrophages, unlike the S. Typhimurium references, which were unrecoverable. Infection with S. Uganda stimulated increased cytokine (CXCL8, IL1B and TNF) and chemokine (CCL2, CCL3 and CCL22) release, compared to the reference strain.

SPI-13, containing the lgl-ripABC operon, in addition to three uncharacterised genes, has ,currently, only been reported to be highly up-regulated within macrophages. Salmonella Uganda CFSAN006159, which has been shown, in this study, to readily survive in THP-1 macrophages, in addition to eliciting a large proinflammatory response, uniquely harbours two complete chromosomal copies of SPI-13, located approximately 460-kbp apart. Bioinformatic analyses suggests that these loci appear to have been acquired from distinct genetic lineages. This finding may contribute to the extreme pathogenicity of this isolate during infection resulting from a gene dosage effect.

Significance: Characterising the phenotypic virulence and genomic diversity of this serovar further extends our understanding of its ability to illicit a host-cell response during infection.

Back to: Technical Session 4 – Molecular Characterisation of Microorganisms
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