Pathogenicity of Clinical Salmonella enterica Serovar Typhimurium Isolates from Thailand in a Mouse Colitis Model

Salmonella enterica serovar Typhimurium (S. Typhimurium, STM) is a leading cause of non-typhoidal salmonellosis (NTS) worldwide. The pathogenesis of NTS has been studied extensively using a streptomycin-pretreated mouse colitis model with the limited numbers of laboratory S. Typhimurium strains. However, the pathogenicity of the clinically isolated S. Typhimurium (STMC) strains endemic in Thailand in mice has not been explored. The aim of this study was to compare the pathogenicity of STMCs collected from Northern Thailand to the laboratory S. Typhimurium strain (IR715) in mice. Five STMC isolates were obtained from the stool cultures of acute NTS patients admitted to Maharaj Nakorn Chiang Mai Hospital in 2016 and 2017. Detection of virulence genes and sequence type (ST) of the strains was done. Female C57BL/6 mice were pretreated with streptomycin sulfate one day prior to oral infection with Salmonella. At Day 4 post-infection, mice were euthanized, and tissues were collected to analyze the bacterial numbers, tissue inflammation and cecal histopathological score. We found that all five STMCs are ST34 and conferred the same or reduced pathogenicity compared to that of IR715 in mice. A strain-specific effect of ST34 on mouse gut colonization was also observed. Thailand STM ST34 exhibited a significant attenuated systemic infection in mice possibly due to the lack of spvABC-containing virulence plasmid. This article is protected by copyright. All rights reserved.