The Effect of Antimicrobial Treatment upon the Gill Bacteriome of Atlantic Salmon (Salmo salar L.) and Progression of Amoebic Gill Disease (AGD) In Vivo.

Joel Slinger,James W Wynne,Chris N Stratford,Mark B Adams,Megan Rigby

doi:10.3390/microorganisms9050987

Abstract

Branchial surfaces of finfish species contain a microbial layer rich in commensal bacteria which can provide protection through competitive colonization and production of antimicrobial products. Upon disturbance or compromise, pathogenic microbiota may opportunistically infiltrate this protective barrier and initiate disease. Amoebic gill disease (AGD) is a globally significant health condition affecting salmonid mariculture. The current study examined whether altering the diversity and/or abundance of branchial bacteria could influence the development of experimentally induced AGD. Here, we challenged Atlantic salmon (Salmo salar) with Neoparamoeba perurans in a number of scenarios where the bacterial community on the gill was altered or in a state of instability. Administration of oxytetracycline (in-feed) and chloramine-T (immersion bath) significantly altered the bacterial load and diversity of bacterial taxa upon the gill surface, and shifted the community profile appreciably. AGD severity was marginally higher in fish previously subjected to chloramine-T treatment following 21 days post-challenge. This research suggests that AGD progression and severity was not clearly linked to specific bacterial taxa present in these systems. However, we identified AGD associated taxa including known pathogenic genus (Aliivibrio, Tenacibaculum and Pseudomonas) which increased in abundance as AGD progressed. Elucidation of a potential role for these bacterial taxa in AGD development is warranted.

Highlights

Teleost fish mucosa is a functionally important tissue constructed of macromolecules and polymers containing numerous enzymes and protective peptides [1,2]
The mucosal bacterial community plays a key role in health and vitality of fish, yet we have limited understanding of the effect that commensal bacterial imbalance plays in disease susceptibility
We compared the progression of Amoebic gill disease (AGD) between groups of Atlantic salmon with modulated gill bacterial communities, and assessed the role of bacterial taxa in AGD development

Summary

Introduction

Teleost fish mucosa is a functionally important tissue constructed of macromolecules and polymers containing numerous enzymes and protective peptides [1,2]. The mucosa forms a structural medium that facilitates colonization of beneficial microbiota which play a key role in the health and function of the animal [3,4]. The bacterial community which colonize the mucosal layer contains both transient and resident taxa which utilize available resources [5] and perform key roles such as competitive exclusion or inhibition of unwanted pathogens [6,7,8,9]. Environmental stressors or disease can lead to a dysbiosis of mucosal bacterial communities in an aquatic setting [12]. Rapid temperature reduction and air exposure applied to the late egg developmental stages significantly affected the gut and skin community of larval Atlantic salmon (Salmo salar) [13].

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