Characterization of a Broad-Host-Range Lytic Phage SHWT1 Against Multidrug-Resistant Salmonella and Evaluation of Its Therapeutic Efficacy in vitro and in vivo.

Chenglin Tao,Chan Ding,Jingjing Qi,Song Gao,Shaohui Wang,Tao Li,Hong Zhu,Shengqing Yu,Yaodong Zhang,Dossêh Jean Apôtre Afayibo,Yao Wang,Zhengfei Yi,Mingxing Tian

doi:10.3389/fvets.2021.683853

Abstract

Inappropriate use of antibiotics has accelerated to the emergence of multidrug-resistant bacteria, becoming a major health threat. Moreover, bacterial biofilms contribute to antibiotic resistance and prolonged infections. Bacteriophage (phage) therapy may provide an alternative strategy for controlling multidrug-resistant bacterial infections. In this study, a broad-host-range phage, SHWT1, with lytic activity against multidrug-resistant Salmonella was isolated, characterized and evaluated for the therapeutic efficacy in vitro and in vivo. Phage SHWT1 exhibited specific lytic activity against the prevalent Salmonella serovars, such as Salmonella Pullorum, Salmonella Gallinarum, Salmonella Enteritidis, and Salmonella Typhimurium. Morphological analysis showed that phage SHWT1 was a member of the family Siphoviridae and the order Caudovirales. Phage SHWT1 had a latent period of 5 min and burst size of ~150 plaque-forming units (PFUs)/cell. The phage was stable from pH 3-12 and 4–65°C. Phage SHWT1 also showed capacity to lyse Salmonella planktonic cells and inhibit the biofilm formation at optimal multiplicity of infection (MOI) of 0.001, 0.01, 0.1, and 100, respectively. In addition, phage SHWT1 was able to lyse intracellular Salmonella within macrophages. Genome sequencing and phylogenetic analyses revealed that SHWT1 was a lytic phage without toxin genes, virulence genes, antibiotic resistance genes, or significant genomic rearrangements. We found that phage SHWT1 could successfully protect mice against S. enteritidis and S. typhimurium infection. Elucidation of the characteristics and genome sequence of phage SHWT1 demonstrates that this phage is a potential therapeutic agent against the salmonellosis caused by multidrug-resistant Salmonella.

Highlights

Salmonella is a Gram-negative bacterium that is an important pathogen of humans and animals
We found that phage SHWT1 was able to eliminate the formed biofilm and lyse the bacterial cells (P < 0.05 and P < 0.01) (Figures 5C,D)
The bacterial reduction test in this study indicated that growth of multidrug-resistant Salmonella was constantly inhibited for at least 8 h in the presence of phage SHWT1 at optimal multiplicity of infection (MOI)

Summary

Introduction

Salmonella is a Gram-negative bacterium that is an important pathogen of humans and animals. Salmonella is a leading etiological agent associated with outbreaks of food-borne illness worldwide, commonly resulting in global economic losses [1,2,3]. Animals, including poultry are a main reservoir for Salmonella, such as the prevalent Salmonella serovars Salmonella Pullorum Typhimurium) [4,5,6,7,8,9,10]. Some of these serovars can lead to serious zoonotic diseases via contaminated foods such as poultry and eggs

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Discussion

Conclusion