Gene Sequencing and Phylogenetic Analysis: Powerful Tools for an Improved Diagnosis of Fish Mycobacteriosis Caused by Mycobacterium fortuitum Group Members.

Davide Mugetti,Vasco Menconi,Giuseppe Esposito,Mattia Tomasoni,Alessandro Dondo,Paolo Pastorino,Marino Prearo

doi:10.3390/microorganisms9040797

Abstract

The Mycobacterium fortuitum group (MFG) consists of about 15 species of fast-growing nontuberculous mycobacteria (NTM). These globally distributed microorganisms can cause diseases in humans and animals, especially fish. The increase in the number of species belonging to MFG and the diagnostic techniques panel do not allow to clarify their real clinical significance. In this study, biomolecular techniques were adopted for species determination of 130 isolates derived from fish initially identified through biochemical tests as NTM belonging to MFG. Specifically, gene sequencing and phylogenetic analysis were used based on a fragment of the gene encoding the 65 KDa heat shock protein (hsp65). The analyzes made it possible to confirm that all the isolates belong to MFG, allowing to identify the strains at species level. Phylogenetic analysis substantially confirmed what was obtained by gene sequencing, except for six strains; this is probably due to the sequences present in NCBI database. Although the methodology used cannot represent a univocal identification system, this study has allowed us to evaluate its effectiveness as regards the species of MFG. Future studies will be necessary to apply these methods with other gene fragments and to clarify the real pathogenic significance of the individual species of this group of microorganisms.

Highlights

IntroductionThe Mycobacterium fortuitum group (MFG) includes several rapidly growing nontuberculous mycobacteria (NTM) with very similar cultural, biochemical, and molecular features
Strains of nontuberculous mycobacteria (NTM) isolated from fish identified by biochemical tests as Mycobacterium fortuitum group (MFG) members were selected during the years 2015–2019
The analyzed mycobacteria were mainly recovered from aquarium fish (109/130, p = 83.8%); the remaining microorganisms came from farmed fish species (21/130, p = 16.2%)

Summary

Introduction

The Mycobacterium fortuitum group (MFG) includes several rapidly growing nontuberculous mycobacteria (NTM) with very similar cultural, biochemical, and molecular features. The group takes its name from the most representative species, Mycobacterium fortuitum, described for the first time in 1938 [1] and included in group IV (rapid growers mycobacteria) of the Runyon’s classification [2]. With the improvement of diagnostic techniques, this group has undergone several additions and taxonomic changes as happened for most species of the genus Mycobacterium. This is evident in the founding species of MFG, divided into two subspecies, M. fortuitum subsp. This is evident in the founding species of MFG, divided into two subspecies, M. fortuitum subsp. fortuitum and M. fortuitum subsp

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