Genetic diversity, anti‐microbial resistance, plasmid profile and frequency of the Vi antigen in Salmonella Dublin strains isolated in Brazil

Abstract

SummarySalmonella Dublin is strongly adapted to cattle causing enteritis and/or systemic disease with high rates of mortality. However, it can be sporadically isolated from humans, usually causing serious disease, especially in patients with underlying chronic diseases.The aim of this study was to molecularly type S. Dublin strains isolated from humans and animals in Brazil to verify the diversity of these strains as well as to ascertain possible differences between strains isolated from humans and animals. Moreover, the presence of the capsular antigen Vi and the plasmid profile was characterized in addition to the anti-microbial resistance against 15 drugs. For this reason, 113 S. Dublin strains isolated between 1983 and 2016 from humans (83) and animals (30) in Brazil were typed by PFGE and MLVA. The presence of the capsular antigen Vi was verified by PCR, and the phenotypic expression of the capsular antigen was determined serologically. Also, a plasmid analysis for each strain was carried out. The strains studied were divided into 35 different PFGE types and 89 MLVA-types with a similarity of ≥80% and ≥17.5%, respectively. The plasmid sizes found ranged from 2 to >150 kb and none of the strains studied presented the capsular antigen Vi. Resistance or intermediate resistance was found in 23 strains (20.3%) that were resistant to ampicillin, ciprofloxacin, chloramphenicol, imipenem, nalidixic acid, piperacillin, streptomycin and/or tetracycline. The majority of the S. Dublin strains studied and isolated over a 33-year period may descend from a common subtype that has been contaminating humans and animals in Brazil and able to cause invasive disease even in the absence of the capsular antigen. The higher diversity of resistance phenotypes in human isolates, as compared with animal strains, may be a reflection of the different anti-microbial treatments used to control S. Dublin infections in humans in Brazil. K E Y W O R D Santigen Vi, anti-microbial resistance, multiple-locus variable-number tandem-repeat analysis, plasmid analysis, pulsed-field gel electrophoresis, Salmonella Dublin

High similarity and high frequency of virulence genes among Salmonella Dublin strains isolated over a 33-year period in Brazil

“…Similar to MLST, both methodologies grouped the strains independently of geographical, temporal, or isolation source characteristics, which reinforced the idea from previous studies of Salmonella Dublin strains from Brazil performed by our research group that suggest that these strains may have descended from a common ancestor that has little differentiated over the years [13]. In the previous study of our research group [13], the same 112 S. Dublin strains of this study were typed by pulsed-field gel electrophoresis (PFGE) and multilocus variable-number tandem repeat analysis (MLVA). Similar to the results found in the present study, PFGE also grouped the strains in a single cluster, with a similarity of ≥ 80.7%.…”

“…Salmonella Dublin is a serovar strongly adapted to bovine hosts, but can be sporadically isolated from human clinical cases [1,2]. Different molecular typing techniques have been used for epidemiological studies of S. Dublin strains worldwide [9][10][11][12][13]. The advancement in whole-genome sequencing allowed the sequencing of large sets of strains and the characterization by classic or newly developed methodologies, such as MLST and CRISPR [18,19].…”

“…A total of 112 Salmonella Dublin strains isolated in Brazil from humans (82) between 1983 and 2016, and animals (30) between 1992 and 2015 were studied. These strains were previously described in Vilela et al 2018 [13] and are representative isolates of the years, states, material, and source of isolation of the collections of two Salmonella reference laboratories in Brazil, the Adolfo Lutz Institute of São Paulo (IAL-SP), and Oswaldo Cruz Foundation of Rio de Janeiro (FIOCRUZ-RJ). Supporting Information Table S1 presents the year, source, and states of isolation of the 112 S. Dublin strains studied.…”

“…Some methodologies such as pulsed-field gel electrophoresis (PFGE), multiple-locus variable-number of tandem repeats analysis (MLVA), enterobacterial repetitive intergenic consensus PCR (ERIC-PCR), multilocus enzyme electrophoresis (MLEE), multilocus sequence typing (MLST), and clustered regularly interspaced short palindromic repeats (CRISPR) have been successfully used to subtype strains of many Salmonella serovars, including S. Dublin [9][10][11][12][13]. Although the great applicability, some methodologies, such as MLST and CRISPR, require excessive laboratory work and high costs that restricts the performing of these methodologies to small and representative sets of strains [14][15][16][17].…”

“…Few information is available about the molecular epidemiology of S. Dublin strains isolated worldwide, and most of the studies did not study sets of strains exclusively of this serovar, interfering on the understanding of the specific characteristics and traits of S. Dublin [9][10][11][12]29]. Specifically in Brazil, only five studies molecularly typed strains of this serovar, among which, only two analyzed a large set exclusive of S. Dublin strains, making it difficult to evaluate the diversity of strains of this serovar circulating in this country [13,[30][31][32][33]. Furthermore, MLST, CRISPR, and CRISPR-MVLST have never been used for typing strains of this serovar in Brazil, according to the published literature.…”