Phenotypic and genotypic characterization of Salmonella Typhimurium isolates from humans and foods in Brazil.

Amanda Aparecida Seribelli,Marc W Allard,Fernanda Almeida,Marta Inês Cazentini Medeiros,Mario H Paziani,Dália Dos Prazeres Rodrigues,Marcia R Von Zeska Kress,Juliana Pfrimer Falcão,Marcelo Ferreira Cruz,Felipe Pinheiro Vilela,Miliane Rodrigues Frazão,Yung-Fu Chang

doi:10.1371/journal.pone.0237886

Abstract

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.

Highlights

Salmonella Typhimurium has been an important cause of gastroenteritis in different parts of the globe [1,2,3]
Typhimurium isolates studied (32.5% isolated from humans and 35% isolated from food) invaded the epithelial cells at various levels compared to the SL1344 reference (Fig 1)
Typhimurium isolates that invaded more than the SL1344 reference in groups from A to G

Summary

Introduction

Salmonella Typhimurium has been an important cause of gastroenteritis in different parts of the globe [1,2,3]. The transmission can occur person-to-person by fecal oral routes and, contaminated asymptomatic pets can transmit to humans [4]. According to the Centers for Disease Control and Prevention (CDC) (2020), it was estimated that 1.35 million infections, 26,500 hospitalizations and 420 deaths occur in the United States every year due to salmonellosis [5]. In humans the symptoms are diarrhea, fever, and stomach cramps, with food being the main source of transmission of this disease. For prevention and control of Salmonella spp. food safety and hygenic handling practices are very important [5]

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