Mycobacterium pseudoshottsii in Mediterranean Fish Farms: New Trouble for European Aquaculture?

Davide Mugetti,Simona Zoppi,Vasco Menconi,Katia Varello,Marino Prearo,Daniela Florio,Paolo Pastorino,Alessandro Dondo,Andrea Gustinelli,Maria Letizia Fioravanti,Elena Bozzetta

doi:10.3390/pathogens9080610

Abstract

Mycobacterium pseudoshottsii, a slow-growing mycobacterium closely related to M. marinum, has been isolated only in wild fish in the United States and in Japanese fish farms to date. Here, we report cases of mortality in three farmed fish species (Dicentrarchus labrax, Sparus aurata, and Sciaenops ocellatus) caused by M. pseudoshottsii in Italy. Samples underwent necropsy, histology, and culture with pathogen identification based on PCR and sequencing of housekeeping genes (16S rRNA, hsp65, rpoB). Multifocal to coalescing granulomatous and necrotizing inflammation with acid-fast bacilli were observed in the parenchymatous organs, from which M. pseudoshottsii was isolated and identified. Phylogenetic analysis confirmed the results of gene sequencing and allowed subdivision of the isolates into three distinct groups. M. pseudoshottsii poses a potential threat for Mediterranean aquaculture. Its origin in the area under study needs to be clarified, as well as the threat to the farmed fish species.

Highlights

The scientific literature attributes a predominant role to Mycobacterium marinum in the onset of fish mycobacteriosis [1,2]
The present study reports on several several mycobacteriosis events caused by pseudoshottsii in three marine fish farms in several mycobacteriosis events caused by M. pseudoshottsii in three marine fish farms in Italy
M. marinum is the main cause of clinical mycobacteriosis, new mycobacterial species responsible for mortality

Summary

Introduction

The scientific literature attributes a predominant role to Mycobacterium marinum in the onset of fish mycobacteriosis [1,2]. The use of biomolecular techniques in the diagnosis of mycobacteriosis has led to the discovery of many new etiological agents [6], including M. shottsii and M. pseudoshottsii, which are closely related to. Both species were characterized following an epizootic event with mortality of wild striped bass (Morone saxatilis) in Chesapeake Bay, Maryland, USA [7,8,9,10]. M. pseudoshottsii has expanded its distribution area and range of fish species affected. It was first diagnosed in 2007 in white perch (Morone americana) in two rivers in Maryland (Rhode and Corsica rivers) and again in striped bass from Rockaway Beach, New York City [12]. Chesapeake Bay remained the most interesting area for Pathogens 2020, 9, 610; doi:10.3390/pathogens9080610 www.mdpi.com/journal/pathogens

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