Title: Characterization of the mobilome of invasive non-typhoidal Salmonella Dublin
Authors: Manal Mohammeda, Sabrina Cadel-Sixb,c, Marie-Leone Vignaudb,c, Myron M. Levined
aSchool of Life Sciences, University of Westminster, London, UK.
bUniversité Paris-Est, Marne-la-Vallée, France
cANSES, Laboratory for Food Safety, Salmonella and Listeria Unit, Maisons-Alfort, France
dCenter for Vaccine Development, School of Medicine, University of Maryland, USA.
Human infection by non-typhoidal Salmonella Dublin is mainly characterised by self-limiting gastrointestinal illness. However, a proportion of cases are associated with invasive illness (bacteraemia, septicaemia and meningitis). The genetic basis of invasiveness of S. Dublin in humans is not well characterised. Acquisition of mobile genetic elements (MGEs) might contribute to bacterial virulence. The aim of this study is to characterize the mobilome of S. Dublin.
A set of S. Dublin isolates from human invasive and non-invasive (gastroenteritis) cases and from veterinary cases were selected for whole genome sequencing (WGS). Isolates included 12 human invasive isolates from blood of children admitted to l'Hôpital Gabriel Touré in Mali with fever and severe clinical illness. For comparison, we included 10 clinical non-invasive isolates and 8 veterinary isolates from raw milk and raw milk cheeses. WGS of multiplexed libraries was carried out on Illumina HiSeq using 250bp PE protocol. De novo assembly was carried out using SPAdes and draft genomes were annotated using Prokka.
S. Dublin strains harbour several MGEs including the S. Dublin virulence plasmid, Salmonella pathogenicity islands; SPI-6 and SPI-19 harbouring T6SSs and the novel pathogenicity island ST313-GI. Interestingly, Vi antigen was present in two veterinary strains but was absent from other strains indicating that Vi antigen is not the main virulence determinant in S. Dublin.
WGS revealed several MGEs forming the mobilome of S. Dublin that may contribute to bacterial virulence. Comparative transcriptomics will be carried out to identify differentially expressed genes in invasive strains compared with non-invasive and veterinary strains.