Bacteriophage-Insensitive Mutants of Antimicrobial-Resistant Salmonella Enterica are Altered in their Tetracycline Resistance and Virulence in Caco-2 Intestinal Cells.

Karen Fong,Jean-Guillaume Rheault,Siyun Wang,Kaiwen Mu,Pascal Delaquis,David D Kitts,Roger C Levesque,Lawrence Goodridge

doi:10.3390/ijms21051883

Abstract

Bacteriophages have shown promise as therapeutic alternatives to antibiotics for the control of infectious bacteria, including the human pathogen Salmonella. However, the development of effective phage-based applications requires the elucidation of key interactions between phages and target hosts, particularly since host resistance to phage is inevitable. Little is known about the alteration of host phenotypes following the development of resistance to phage. The aim of this study is to evaluate the antibiotic susceptibility and virulence of a Salmonella isolate following the development of resistance to bacteriophage SI1. We observed enhanced susceptibility to tetracycline and decreased invasion capacity in a differentiated Caco-2 intestinal cell line. Whole genome sequence analysis revealed an array of mutations, most notably, truncations in vgrG1_2, a core gene involved in Type VI secretion and mutations in the lipopolysaccharide, thereby indicating the plausible attachment site of phage SI1. These findings shed light on understanding the underlying mechanism for phage immunity within the host. Importantly, we reveal an associated genetic cost to the bacterial host with developing resistance to phages. Taken together, these results will aid in advancing strategies to delay or eliminate the development of host resistance when designing informed phage-based antimicrobials.

Highlights

The foodborne pathogen non-typhoidal Salmonella causes 93 million enteric infections, resulting in more than 150,000 deaths and 4,847,000 disability-adjusted life years lost worldwide per annum [1,2]
Given the frequency of infections and the multiplicity of potential vehicles of transmission, the rise of antimicrobial resistance (AMR) in Salmonella is of particular concern. [6,7]
Fitness costs have been shown to vary across genera and species of bacteria [18], only nominal work has been performed with foodborne pathogens such as Salmonella

Summary

Introduction

The foodborne pathogen non-typhoidal Salmonella causes 93 million enteric infections, resulting in more than 150,000 deaths and 4,847,000 disability-adjusted life years lost worldwide per annum [1,2]. Salmonellosis is generally self-limiting in developed countries, chronic complications may arise, including reactive arthritis and chronic gastroenteritis [3]. The ability of this pathogen to colonize diverse niches has led to its persistence and survival in a range of foods that may serve as vehicles of transmission, including poultry, eggs, meat, dairy products, fresh produce, and a variety of ready-to-eat products [4,5]. Interest in the use of bacteriophages (phages) as alternative therapeutic agents for the treatment of infections caused by AMR bacteria has increased in recent years [7]. We hypothesize here that BIMs of Salmonella may exhibit increased susceptibility to antibiotics and decreased virulence potential

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