Aims:To characterize the genetic relatedness, phenotypic and genotypic antimicrobial resistance and plasmid content of 80 Salmonella Infantis strains isolated from food, humans and veterinary sources from 2013 to 2018 in Brazil. Methods and results:Pulsed-field gel electrophoresis and single-nucleotide polymorphism analysis showed major clusters containing 50% and 38.8% of the strains studied respectively. Multilocus sequence typing assigned all strains to ST32. Diskdiffusion revealed that 90% of the strains presented resistant or intermediate resistant profiles and 38.8% displayed multidrug resistance. Resistance genes for aminoglycosides (aac(6′)-Iaa; aadA12; aph(3″-Ib; aph(6)-Id), βlactams (bla TEM-1 ; bla CTX-M-8 ; bla CMY-2 ), trimethoprim (dfrA8), tetracycline (tet(A)), amphenicols (floR), sulfonamide (sul2), efflux pumps (mdsA; mdsB), chromosomal point mutations in gyrB, parC, acrB and pmrA were detected. Strains harboured

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Resistance of Salmonella Dublin strains to quinolones and tetracycline has been increasing worldwide. Studies regarding the genotypic resistance traits of strains of this serovar isolated in Brazil are scarce. This study aims to examine the genetic characteristics of Salmonella Dublin strains isolated in Brazil, which are associated with resistance to quinolone and tetracycline. The minimum inhibitory concentrations (MICs) of nalidixic acid, ciprofloxacin, and tetracycline of the 10 strains sensitive and 21 strains resistant to quinolone and tetracycline were determined using Etest. The mutation profiles of the gyrA, gyrB, parC, and parE genes were accessed by sequencing, while the presence of plasmid-mediated quinolone resistance and tet genes was analyzed by PCR. Quinolone-resistant strains presented the amino acid substitutions Ser96→Tyr, Ser96→Phe, Asp107→Asn, or Asp108→Gly on the gyrA gene, and the Ser224→Phe and Glu231→Asp mutations on the gyrB gene. The qnrA, tet(A), and tet(B) genes were detected in 5, 13, and 6 strains, respectively. Analysis of the MIC values revealed that 1 and 3 strains presented intermediate and resistant MIC profiles to nalidixic acid, respectively; 6 strains presented intermediate MIC profile to ciprofloxacin; and 13 strains presented resistant MIC profile to tetracycline. In the Salmonella Dublin strains studied, quinolone resistance was mainly related to mutation points that led to target alteration in the gyrA and gyrB genes, while tetracycline resistance was associated with the presence of tet(A) and/or tet(B) genes, with the highest resistance levels detected in strains bearing the tet(B) gene. The presence of the aforementioned genotypic resistance traits in Salmonella Dublin strains isolated over 33 years in Brazil indicates that ciprofloxacin or tetracycline therapy against such strains may fail.

Salmonella enterica subsp. enterica serovar Typhimurium (S. Typhimurium) causes gastroenteritis in many countries. However, in Brazil there are few studies that have conducted a virulence characterization of this serovar. The aim of this study was to evaluate the virulence potential of S. Typhimurium strains isolated in Brazil. Forty S. Typhimurium strains isolated from humans (n = 20) and food (n = 20) from Brazil were studied regarding their invasion and survival in human epithelial cells (Caco-2) and macrophages (U937). Their virulence potential was determined using the Galleria mellonella larvae model combined with the analysis of virulence genes by whole genome sequencing (WGS). A total of 67.5% of the S. Typhimurium studied (32.5% isolated from humans and 35% isolated from food) invaded Caco-2 epithelial cells at levels similar to or greater than the S. Typhimurium SL1344 prototype strain. In addition, 37.5% of the studied strains (25% isolated from humans and 12.5% isolated from food) survived in U937 human macrophages at levels similar to or greater than SL1344. S. Typhimurium strains isolated from humans (40%) and food (25%) showed high or intermediate virulence in G. mellonella larvae after seven days exposure. Approximately, 153 virulence genes of chromosomal and plasmidial origin were detected in the strains studied. In conclusion, the ability of the S. Typhimurium to invade Caco-2 epithelial cells was strain dependent and was not related to the source or the year of isolation. However, S. Typhimurium strains isolated from humans showed greater survival rates in U937 human macrophages, and presented higher proportion of isolates with a virulent profile in G. mellonella in comparison to strains isolated from food suggesting that this difference may be related to the higher frequency of human isolates which contained plasmid genes, such as spvABCDR operon, pefABCD operon, rck and mig-5.

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