Abstract
After Salmonella Enteritidis and S. Typhimurium, S. 4,[5],12:i:- is the most reported serovar in human clinical cases. During the past 20 years, many tools have been used for its typing and second-phase flagellar deletion characterization. Currently, whole genome sequencing (WGS) and different bioinformatic programs have shown the potential to be more accurate than earlier tools. To assess this potential, we analyzed by WGS and in silico typing a selection of 42 isolates of S. 4,[5],12:i:- and S. Typhimurium with different in vitro characteristics. Comparative analysis showed that SeqSero2 does not differentiate fljB-positive S. 4,[5],12:i:- strains from those of serovar Typhimurium. Our results proved that the strains selected for this work were non-clonal S. 4,[5],12:i:- strains circulating in Spain. Using WGS data, we identified 13 different deletion types of the second-phase flagellar genomic region. Most of the deletions were generated by IS26 insertions, showing orientation-dependent conserved deletion ends. In addition, we detected S. 4,[5],12:i:- strains of the American clonal line that would give rise to the Southern European clone in Spain. Our results suggest that new S. 4,[5],12:i:- strains are continuously emerging from different S. Typhimurium strains via different genetic events, at least in swine products.
Highlights
Salmonella enterica subs. enterica consist of more than 2600 serovars [1]
We found eight strains S. 4,[5],12:i:- with an ASSuT tetra-resistance but none of these strains had the multidrug resistance plasmid described by Garcia et al In six of these strains, only one or two copies of IS26 were detected in the second-phase flagellar genomic region and the remaining two S. 4,[5],12:i:- ASSuT strains were classified as ∆fljAB10 deletion type, showing a 7663 bp fragment between STM2761 and iroB genes
These tools were essential to study the genetic bases of the monophasic phenotype and to identify S. 4,[5],12:i:- American clonal line strains in Spain that would give rise to the Southern Europe clone due to the acquisition of the IncR plasmid
Summary
Salmonella enterica subs. enterica consist of more than 2600 serovars [1]. Nontyphoidal Salmonella serovars are common causative zoonotic agents of bacterial food-borne disease worldwide. Enterica consist of more than 2600 serovars [1]. Nontyphoidal Salmonella serovars are common causative zoonotic agents of bacterial food-borne disease worldwide. The first described monophasic variant of S. Typhimurium emerged in Spain in 1997 [3] and became the fourth most common serovar in clinical isolates in 1998 [4]. Thereafter, the emergence of multiple clones of monophasic variant of S. Typhimurium has been reported worldwide [5]. According to data from seven European countries, reported to The European Surveillance System (TESSy), the clinical isolates of S. 4,[5],12:i:- is still the third most common serovar with 126 cases reported in 2016 [6] In Spain, S. 4,[5],12:i:- is still the third most common serovar with 126 cases reported in 2016 [6]
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