Abstract
Salmonella 4,[5],12:i:- are monophasic S. Typhimurium variants incapable of producing the second-phase flagellar antigen. They have emerged since the mid-1990s to become one of the most prevalent Salmonella serotypes causing human disease world-wide. Multiple genetic events associated with different genetic elements can result in the monophasic phenotype. Several jurisdictions have reported the emergence of a Salmonella 4,[5],12:i:- clone with SGI-4 and a genetic element (MREL) encoding a mercury resistance operon and antibiotic resistance loci that disrupts the second phase antigen region near the iroB locus in the Salmonella genome. We have sequenced 810 human and animal Canadian Salmonella 4,[5],12:i:- isolates and determined that isolates with SGI-4 and the mercury resistance element (MREL; also known as RR1&RR2) constitute several global clades containing various proportions of Canadian, US, and European isolates. Detailed analysis of the data provides a clearer picture of how these heavy metal elements interact with bacteria within the Salmonella population to produce the monophasic phenotype. Insertion of the MREL near iroB is associated with several deletions and rearrangements of the adjacent flaAB hin region, which may be useful for defining human case clusters that could represent outbreaks. Plasmids carrying genes encoding silver, copper, mercury, and antimicrobial resistance appear to be derived from IS26 mediated acquisition of these genes from genomes carrying SGI-4 and the MREL. Animal isolates with the mercury and As/Cu/Ag resistance elements are strongly associated with porcine sources in Canada as has been shown previously for other jurisdictions. The data acquired in these investigations, as well as from the extensive literature on the subject, may aid source attribution in outbreaks of the organism and interventions to decrease the prevalence of this clone and reduce its impact on human disease.
Highlights
Salmonella enterica subsp. enterica serovar 4,[5],12:i:- is an emerging S
Because of the density of data represented in this diagram and the difficulty of assigning membership to clades inherent in the reduction of a three-dimensional representation, we looked at the clade structure in the original dendrogram (S3 Fig) used to construct the MSTs in BioNumerics
Salmonella 4,[5],12:i:- isolates containing SGI-4 and the mercury resistance element (MREL) are only part of the total Canadian 4,[5],12:i:- population characterized in this work
Summary
Salmonella enterica subsp. enterica serovar 4,[5],12:i:- is an emerging S. Enterica serovar 4,[5],12:i:- is an emerging S. Typhimurium monophasic variant that has dramatically increased in prevalence world-wide since the mid-1990s [1,2,3]. During this same period the prevalence of S. Enteritidis has dramatically increased in Canada [4]. For the last seven years, Salmonella 4, [5],12:i:- has been the 4th or 5th most prevalent Salmonella serotype, or higher, in Canada [4,5], Europe [1], the U.S [6], and other countries [7,8,9,10]
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