Phage Cocktail Development against Aeromonas salmonicida subsp. salmonicida Strains Is Compromised by a Prophage.

Nava Hosseini,Mahdi Chehreghani,Sylvain Moineau,Steve J Charette,Valérie E Paquet

doi:10.3390/v13112241

Abstract

Aquaculture is a rapidly growing food production sector. Fish farmers are experiencing increasing problems with antibiotic resistance when fighting against pathogenic bacteria such as Aeromonas salmonicida subsp. salmonicida, the causative agent of furunculosis. Phage therapy may provide an alternative, but effective use must be determined. Here, we studied the inhibition of A. salmonicida subsp. salmonicida strains by five phages (HER98 [44RR2.8t.2], HER110 [65.2], SW69-9, L9-6 and Riv-10) used individually or as combinations of two to five phages. A particular combination of four phages (HER98 [44RR2.8t.2], SW69-9, Riv-10, and HER110 [65.2]) was found to be the most effective when used at an initial multiplicity of infection (MOI) of 1 against the A. salmonicida subsp. salmonicida strain 01-B526. The same phage cocktail is effective against other strains except those bearing a prophage (named Prophage 3), which is present in 2/3 of the strains from the province of Quebec. To confirm the impact of this prophage, we tested the effectiveness of the same cocktail on strains that were either cured or lysogenized with Prophage 3. While the parental strains were sensitive to the phage cocktail, the lysogenized ones were much less sensitive. These data indicate that the prophage content of A. salmonicida subsp. salmonicida can affect the efficacy of a cocktail of virulent phages for phage therapy purposes.

Highlights

We show that a four-phage cocktail (HER98, HER110, SW69-9 and Riv-10) used at an initial multiplicity of infection (MOI) of 1 was the most efficient in the tested conditions
The model bacterial strain chosen for this initial evaluation was A. salmonicida subsp. salmonicida 01-B526
This strain was isolated in the Province of Quebec, possesses an AsaGEI1a and six plasmids but no Prophage 3 [9,27,30]

Summary

Introduction

Furunculosis is a deadly fish disease that causes heavy economic losses in salmonid farming throughout the world [1]. The causative agent of the typical form of furunculosis is Aeromonas salmonicida subspecies salmonicida, which is a psychrophilic, non-motile, Gramnegative aerobic bacilli that produces a water-soluble brown pigment on agar medium [2]. Due to the antibiotic administration in aquaculture worldwide, the number of antibioticresistant strains of A. salmonicida subsp. Salmonicida is increasing [3] As this species is a waterborne pathogen, the probability of horizontal gene transfer with other bacteria likely increases, turning it into a rich reservoir of antibiotic-resistant genes [4,5]. At least 15 plasmids have been found to carry a variety of antibiotic-resistant genes in A. salmonicida species [6]

Objectives

Methods

Results

Conclusion