Abstract
The aim of this study was to characterize the mechanism of fluoroquinolone (FQ) resistance in Salmonella Typhimurium. We established the Caenorhabditis elegans–Salmonella Typhimurium model to select for ciprofloxacin resistance in Salmonella Typhimurium colonizing C. elegans, generating the resistant strains TN4. Gradient doses of ciprofloxacin were used to generate the resistant strain TW4 in vitro. RNA sequencing was used to establish the whole-transcriptome profile of three strains of Salmonella Typhimurium. The gene expression patterns of resistant strains TN4 and TW4 differed from those of the parental strain. In TN4, 2,277 genes were differentially expressed (1,833 upregulated and 444 downregulated) relative to the parental strain, and in TW4, 3,464 genes were differentially expressed (3,433 upregulated and 31 downregulated). Among these differentially expressed genes, 28 were associated with drug resistance and 26 were associated with the two-component systems in the two resistant strains. Seven different pathways were significantly sffected in two strains. Efflux pump overexpression was identified as one of the main mechanisms underlying FQ resistance in the two resistant strains. TW4 differentially expressed more efflux pump genes than TN4 and most of these genes were more strongly expressed than in TN4. However, expression of the efflux pump repressor gene and the mar operon was downregulated in TN4 but not in TW4. Two-component systems are also important in drug resistance. Our findings provide an important basis for further studies of the complex network that regulate FQ resistance in Salmonella.
Highlights
Salmonella species are common zoonotic pathogens of the family Enterobacteriaceae that infect humans and animals, causing gastroenteritis, wound infections, bacteremia and other diseases
Salmonella Typhimurium strain ATCC 13311 and Escherichia coli strain ATCC 25922 were grown on Mueller–Hinton broth (MHB) medium at 37 ̊C
The MIC of ciprofloxacin for the parental strain T0 was less than 0.004 μg/ml
Summary
Salmonella species are common zoonotic pathogens of the family Enterobacteriaceae that infect humans and animals, causing gastroenteritis, wound infections, bacteremia and other diseases. Fluoroquinolones (FQs) are a class of primary antibiotics used in the treatment of Salmonella infections, and their inappropriate use has led to enhanced FQ resistance in Salmonella species [1]. It is important to better understand the mechanisms underlying the increased resistance of Salmonella spp. to controll the generation and propagation of FQ resistance. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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