T2-07 Phenotypic and Pan-genomic Characterization of Salmonella enterica serovar Uganda, an Uncommon Foodborne Pathogen

Monday, July 10, 2017: 10:30 AM
Room 16 (Tampa Convention Center)
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, Center for Food Safety & Applied Nutrition , 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. Little is known about its genetic diversity or pathogenicity of this bacterium.

Purpose: The purpose of this study was to phenotypically characterize 14 isolates and study the pan-genome of Salmonella 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 postinfection. Whole genome sequencing was performed using the Illumina MiSeq platform. A high-quality reference genome for Salmonella Uganda CFSAN006159 was generated on the Pacific Biosciences RS II platform.

Results: In THP-1 macrophages, Salmonella Uganda CFSAN006159 recorded a <two-log reduction between two and 168 hours post infection, whereas Salmonella Uganda CFSAN006173 recorded a < one-log reduction over the same time course. Both Salmonella Uganda isolates persisted for seven days within human macrophages, unlike the Salmonella Typhimurium references which were unrecoverable. Infection with SalmonellaUganda 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 uncharacterized genes, has currently been reported to be highly upregulated only within macrophages. Salmonella Uganda CFSAN006159, which has been shown in this study to survive readily 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 help explain the extreme pathogenicity of this isolate during infection as a result of gene dosage effect.

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