Search

The European epidemic monophasic variant of Salmonella enterica serovar Typhimurium (S. 1 ,4,[5],12:i:-) characterized by the multi locus sequence type ST34 and the antimicrobial resistance ASSuT profile has become one of the most common serovars in Europe (EU) and the United States (US). In this study, we reconstructed the time-scaled phylogeny and evolution of this Salmonella in Europe. The epidemic S. 1 ,4,[5],12:i:- ST34 emerged in the 1980s by an acquisition of the Salmonella Genomic Island (SGI)-4 at the 3′ end of the phenylalanine phe tRNA locus conferring resistance to copper and arsenic toxicity. Subsequent integration of the Tn21 transposon into the fljAB locus gave resistance to mercury toxicity and several classes of antibiotics used in food-producing animals (ASSuT profile). The second step of the evolution occurred in the 1990s, with the integration of mTmV and mTmV-like prophages carrying the perC and/or sopE genes involved in the ability to reduce nitrates in intestinal contents and facilitate the disruption of the junctions of the host intestinal epithelial cells. Heavy metals are largely used as food supplements or pesticide for cultivation of seeds intended for animal feed so the expansion of the epidemic S. 1,4,[5],12:i:- ST34 was strongly related to the multiple-heavy metal resistance acquired by transposons, integrative and conjugative elements and facilitated by the escape until 2011 from the regulatory actions applied in the control of S. Typhimurium in Europe. The genomic plasticity of the epidemic S. 1,4,[5],12:i:- was demonstrated in our study by the analysis of the plasmidome. We were able to identify plasmids harboring genes mediating resistance to phenicols, colistin, and fluoroquinolone and also describe for the first time in six of the analyzed genomes the presence of two plasmids (pERR1744967-1 and pERR2174855-2) previously described only in strains of enterotoxigenic Escherichia coli and E. fergusonii. [ABSTRACT FROM AUTHOR]

Salmonella enterica serovar Typhimurium and Salmonella enterica serovar Derby are the most common serovars of Salmonella enterica ssp. enterica found in pigs in Europe. We previously observed that suckling piglets of sows vaccinated with an S. Typhimurium-based inactivated vaccine are protected against homologous strain challenge. To develop this vaccine for commercial use, potential crossprotectivity of this vaccine to challenge with S. Derby was tested. Two sows were vaccinated with an S. Typhimurium-based inactivated vaccine while two other sows remained serologically negative. Four-day-old suckling piglets from both groups were orally challenged with S. Derby or S. Typhimurium. Maternally-derived immunity against S. Typhimurium protected piglets against S. Typhimurium challenge, when a significant (P < 0.05) decrease in S. Typhimurium count was found in ileocaecal and submandibular lymph node, tonsil, ileum and ileum content. On the other hand, after S. Derby challenge, significant (P < 0.05) decrease in S. Derby count was detected only in ileum content. Although both serovars belong to the same O:4 serogroup, other antigenic structures, for example the flagellin, are different. In a subsequent in-vitro experiment, we found that serum from vaccinated sows inhibited the motility of S. Typhimurium but not the motility of S. Derby. Our results indicate that protectivity of S. Typhimurium vaccine against S. Derby infection is limited. [ABSTRACT FROM AUTHOR]

Antimicrobial-resistantSalmonella entericaposes a particular risk to public health, and in particular isolates belonging to clonal lineages such asSalmonellaTyphimurium DT104 cause epidemics across species including poultry. In recent years, antimicrobial-resistantS. Typhimurium DT193 and specifically the monophasicS. Typhimurium-like variants of this phage type, serotypes 4,12:i:- and 4,5,12:i:-, have become an increasing risk to public health in Europe and the USA and now account for nearly one-half of humanS. Typhimurium infections in the UK. UnlikeS. Typhimurium that possesses two forms of flagella which can vary between phase 1 and phase 2 during infection, monophasic variants possess only phase 1 flagella. These monophasic antimicrobial-resistant variants have become a major problem in pig production but human cases have also been associated with poultry consumption and have been found in UK flocks through surveillance schemes since 2010. In this study we determined the ability of antimicrobial-resistant DT193 serotype 4,12:i:- and 4,5,12:i:- isolates from pigs to infect chickens. All isolates were found to colonize the caeca and liver. All but one isolate of serotype 4,5,12:i:- also infected the spleen. Levels of infection and pathology were comparable with those found with the virulentS. Typhimurium isolate 4/74. These findings indicate that bothS. Typhimurium DT193 and monophasic variants of this phage type usually associated with pigs are capable of colonizing the chicken. This shows that bothS. Typhimurium DT193 and monophasic variants represent a significant and potential emerging threat to poultry production from “spill-over” of these isolates from the pig industry or other sources. [ABSTRACT FROM PUBLISHER]

Salmonella enterica serovar Typhimurium strains from passerines have caused wild bird deaths and human salmonellosis outbreaks in Europe, Oceania, and North America. Here, we performed comparative genomic analysis to explore the emergence, genetic relationship, and evolution of geographically dispersed passerine isolates. We found that passerine isolates from Europe and the United States clustered to form two lineages (EU and US passerine lineages), which were distinct from major S. Typhimurium lineages circulating in other diverse hosts (e.g., humans, cattle, pigs, chickens, and other avian hosts, such as pigeons and ducks). Further, passerine isolates from New Zealand clustered to form a sublineage (NZ passerine lineage) of the US passerine lineage. We inferred that the passerine isolates mutated at a rate of 3.2 × 10 -7 substitutions/site/year, and the US, EU, and NZ passerine lineages emerged in approximately 1952, 1970, and 1996, respectively. Isolates from the three lineages presented genetic similarity, such as lack of antimicrobial resistance genes and accumulation of the same virulence pseudogenes. In addition, genetic diversity due to microevolution existed in the three passerine lineages. Specifically, pseudogenization in the type 1 fimbrial gene fimC (deletion of G at position 87) was detected only in the US and NZ passerine isolates, while single-base deletions in type 3 secretion system effector genes (i.e., gogB , sseJ , and sseK2 ) cooccurred solely in the EU passerine isolates. These findings provide insights into the evolution, host adaptation, and epidemiology of S. Typhimurium in passerines. IMPORTANCE Passerine-associated S. Typhimurium strains have been linked to human salmonellosis outbreaks in recent years. Here, we investigated the phylogenetic relationship of globally distributed passerine isolates and profiled their genomic similarity and diversity. Our study reveals two passerine-associated S. Typhimurium lineages circulating in Europe, Oceania, and North America. Isolates from the two lineages presented phylogenetic and genetic signatures that were distinct from those of isolates from other hosts. The findings shed light on the host adaptation of S. Typhimurium in passerines and are important for source attribution of S. Typhimurium strains to avian hosts. Further, we found that S. Typhimurium definitive phage type 160 (DT160) from passerines, which caused decades-long human salmonellosis outbreaks in New Zealand and Australia, formed a sublineage of the US passerine lineage, suggesting that DT160 might have originated from passerines outside Oceania. Our study demonstrates the importance of whole-genome sequencing and genomic analysis of historical microbial collections to modern epidemiologic surveillance.