title: Virulence Characterisation of Salmonella enterica Isolates of Differing Antimicrobial Resistance Recovered from UK Livestock and Imported Meat Samples.
abstract: Salmonella enterica is a foodborne zoonotic pathogen of significant public health concern. We have characterized the virulence and antimicrobial resistance gene content of 95 Salmonella isolates from 11 serovars by DNA microarray recovered from UK livestock or imported meat. Genes encoding resistance to sulphonamides (sul1, sul2), tetracycline [tet(A), tet(B)], streptomycin (strA, strB), aminoglycoside (aadA1, aadA2), beta-lactam (bla TEM), and trimethoprim (dfrA17) were common. Virulence gene content differed between serovars; S. Typhimurium formed two subclades based on virulence plasmid presence. Thirteen isolates were selected by their virulence profile for pathotyping using the Galleria mellonella pathogenesis model. Infection with a chicken invasive S. Enteritidis or S. Gallinarum isolate, a multidrug resistant S. Kentucky, or a S. Typhimurium DT104 isolate resulted in high mortality of the larvae; notably presence of the virulence plasmid in S. Typhimurium was not associated with increased larvae mortality. Histopathological examination showed that infection caused severe damage to the Galleria gut structure. Enumeration of intracellular bacteria in the larvae 24 h post-infection showed increases of up to 7 log above the initial inoculum and transmission electron microscopy (TEM) showed bacterial replication in the haemolymph. TEM also revealed the presence of vacuoles containing bacteria in the haemocytes, similar to Salmonella containing vacuoles observed in mammalian macrophages; although there was no evidence from our work of bacterial replication within vacuoles. This work shows that microarrays can be used for rapid virulence genotyping of S. enterica and that the Galleria animal model replicates some aspects of Salmonella infection in mammals. These procedures can be used to help inform on the pathogenicity of isolates that may be antibiotic resistant and have scope to aid the assessment of their potential public and animal health risk.
authors.affiliation: Department of Bacteriology, Animal and Plant Health Agency Woking, UK.
authors.forename: Roderick
authors.initials: R
authors.lastname: Card
authors.affiliation: Department of Bacteriology, Animal and Plant Health Agency Woking, UK.
authors.forename: Kelly
authors.initials: K
authors.lastname: Vaughan
authors.affiliation: Department of Bacteriology, Animal and Plant Health Agency Woking, UK.
authors.forename: Mary
authors.initials: M
authors.lastname: Bagnall
authors.affiliation: Department of Pathology, Animal and Plant Health Agency Woking, UK.
authors.forename: John
authors.initials: J
authors.lastname: Spiropoulos
authors.affiliation: Department of Bacteriology, Animal and Plant Health Agency Woking, UK.
authors.forename: William
authors.initials: W
authors.lastname: Cooley
authors.affiliation: Department of Pathology, Animal and Plant Health Agency Woking, UK.
authors.forename: Tony
authors.initials: T
authors.lastname: Strickland
authors.affiliation: Department of Bacteriology, Animal and Plant Health Agency Woking, UK.
authors.forename: Rob
authors.initials: R
authors.lastname: Davies
authors.affiliation: Department of Bacteriology, Animal and Plant Health Agency Woking, UK.
authors.forename: Muna F
authors.initials: MF
authors.lastname: Anjum
keywords: Galleria mellonella; Salmonella enterica; antimicrobial resistance; livestock; virulence