Characterization of Salmonella enterica Serovar Typhimurium Isolates from Pigs and Pig Environment–Related Sources and Evidence of New Circulating Monophasic Strains in Spain

Abstract

A total of 117 Salmonella enterica serovar Typhimurium and 59 monophasic Salmonella Typhimurium (S. enterica serovar 4,[5],12:i:-) strains isolated between 2008 and 2012 from pig, wild bird, rodent, and farm environment samples from the northeast of Spain were characterized by phage typing, antibiotic susceptibility testing, and multiple-locus variable-number tandem repeat analysis in order to evaluate their phenotypic and genetic relatedness. In Salmonella 4,[5],12:i:-, the most prevalent phage types were U311 (40.7%) and DT195 (22%), which did not correspond with the so-called Spanish clone and generally showed a different resistance pattern (ASSuT). Antibiotic resistance was found in 85.8% of the isolates, with 94.1% of them displaying multidrug resistance. Multiple-locus variable-number tandem repeat analysis identified 92 different profiles, six of them shared by both serovars. The minimum spanning tree showed one major cluster that included 95% of the Salmonella 4,[5],12:i:- isolates, which came from different animal sources, geographic locations, and time periods, suggesting high clonality among those Salmonella strains and the ability to spread among pig farms. Overall, isolates of Salmonella 4,[5],12:i:- were more similar to European strains than to the well-characterized Spanish clone. The spread of these new strains of Salmonella 4,[5],12:i:- would likely have been favored by the important pig trade between this Spanish region and other European countries. The overall high prevalence of multidrug resistance observed in these new strains should be noted.

Genomic insights of Salmonella isolated from dry fermented sausage production chains in Spain and France

“…The relevance of S . 1 ,4,[5],12:i:- was raised in the recent decades and the serovar increase observed in France agrees with the information reported from Spain 20 and worldwide 21 . S. 1 ,4,[5],12:i:- was first described as an atypical monophasic S. Typhimurium in 1987 22 and it was spread in Spain during the 1990s 23 .…”

Salmonella Shedding in Slaughter Pigs and the Use of Esterified Formic Acid in the Drinking Water as a Potential Abattoir-Based Mitigation Measure

“…This rise in the prevalence of the monophasic variant of S. Typhimurium appears to be related with some evolutionary advantage, in part likely associated with the accumulation of mobile resistance elements, which in turn would have contributed to its monophasic phenotype [38,39]. In fact, the monophasic variant of S. Typhimurium has been usually characterized by displaying AMR to ampicillin, streptomycin, sulphonamides, and tetracycline (ASSuT) [7,[40][41][42]. Subsequently, it has also been related to resistance to critical antimicrobials for humans, such as third-generation cephalosporins, fosfomycin, and colistin [43][44][45], which has raised concerns about the limitation of antimicrobial therapeutic options.…”

Wild Bonelli’s eagles (Aquila fasciata) as carrier of antimicrobial resistant Salmonella and Campylobacter in Eastern Spain

“…All of these serovars having recently been published in free-living bird studies [1,6,7,40,48], and also in domestic animals (poultry and pigs) and human outbreaks [27]. In addition, S. Typhimurium has been reported as a multidrug antimicrobial resistance bacteria and the most frequent serovar involved in subclinical and clinical infections in birds, such as pigeons, an important feed source for Bonelli's eagles [9,49]. Some strains isolated in this study were resistant to ampicillin and tigecycline.…”