April 21, 2020  |  

Comparative Genomic Analysis of Virulence, Antimicrobial Resistance, and Plasmid Profiles of Salmonella Dublin Isolated from Sick Cattle, Retail Beef, and Humans in the United States.

Salmonella enterica serovar Dublin is a host-adapted serotype associated with typhoidal disease in cattle. While rare in humans, it usually causes severe illness, including bacteremia. In the United States, Salmonella Dublin has become one of the most multidrug-resistant (MDR) serotypes. To understand the genetic elements that are associated with virulence and resistance, we sequenced 61 isolates of Salmonella Dublin (49 from sick cattle and 12 from retail beef) using the Illumina MiSeq and closed 5 genomes using the PacBio sequencing platform. Genomic data of eight human isolates were also downloaded from NCBI (National Center for Biotechnology Information) for comparative analysis. Fifteen Salmonella pathogenicity islands (SPIs) and a spv operon (spvRABCD), which encodes important virulence factors, were identified in all 69 (100%) isolates. The 15 SPIs were located on the chromosome of the 5 closed genomes, with each of these isolates also carrying 1 or 2 plasmids with sizes between 36 and 329?kb. Multiple antimicrobial resistance genes (ARGs), including blaCMY-2, blaTEM-1B, aadA12, aph(3′)-Ia, aph(3′)-Ic, strA, strB, floR, sul1, sul2, and tet(A), along with spv operons were identified on these plasmids. Comprehensive antimicrobial resistance genotypes were determined, including 17 genes encoding resistance to 5 different classes of antimicrobials, and mutations in the housekeeping gene (gyrA) associated with resistance or decreased susceptibility to fluoroquinolones. Together these data revealed that this panel of Salmonella Dublin commonly carried 15 SPIs, MDR/virulence plasmids, and ARGs against several classes of antimicrobials. Such genomic elements may make important contributions to the severity of disease and treatment failures in Salmonella Dublin infections in both humans and cattle.


July 7, 2019  |  

A novel hybrid plasmid carrying multiple antimicrobial resistance and virulence genes in Salmonella enterica serovar Dublin.

Virulence plasmids and antibiotic resistance plasmids are usually maintained separately in Salmonella spp.; however, we report an instance of a hybrid plasmid (pN13-01125) in Salmonella enterica serovar Dublin. Review of the complete sequence of the 172,265-bp plasmid suggests that pN13-01125 is comprised of the previously described pSDVr and pSH696_135 plasmids and that the mechanism of hybridization likely involves IS6 (IS26) insertion sequence elements. The plasmid has a low conjugation frequency, confers resistance to six classes of antimicrobials, and contains a complete spv virulence operon.© Crown copyright 2017.


July 7, 2019  |  

Whole genome analysis of Yersinia ruckeri isolated over 27 years in Australia and New Zealand reveals geographical endemism over multiple lineages and recent evolution under host selection.

Yersinia ruckeri is a salmonid pathogen with widespread distribution in cool-temperate waters including Australia and New Zealand, two isolated environments with recently developed salmonid farming industries. Phylogenetic comparison of 58 isolates from Australia, New Zealand, USA, Chile, Finland and China based on non-recombinant core genome SNPs revealed multiple deep-branching lineages, with a most recent common ancestor estimated at 18?500 years BP (12?355-24?757 95% HPD) and evidence of Australasian endemism. Evolution within the Tasmanian Atlantic salmon serotype O1b lineage has been slow, with 63 SNPs describing the variance over 27 years. Isolates from the prevailing lineage are poorly/non-motile compared to a lineage pre-vaccination, introduced in 1997, which is highly motile but has not been isolated since from epizootics. A non-motile phenotype has arisen independently in Tasmania compared to Europe and USA through a frameshift in fliI, encoding the ATPase of the flagella cluster. We report for the first time lipopolysaccharide O-antigen serotype O2 isolates in Tasmania. This phenotype results from deletion of the O-antigen cluster and consequent loss of high-molecular-weight O-antigen. This phenomenon has occurred independently on three occasions on three continents (Australasia, North America and Asia) as O2 isolates from the USA, China and Tasmania share the O-antigen deletion but occupy distant lineages. Despite the European and North American origins of the Australasian salmonid stocks, the lineages of Y. ruckeri in Australia and New Zealand are distinct from those of the northern hemisphere, suggesting they are pre-existing ancient strains that have emerged and evolved with the introduction of susceptible hosts following European colonization.


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