Virulence Factors of Aeromonas hydrophila: In the Wake of Reclassification.

Cody R. Rasmussen-Ivey,Mark R. Liles,Maria J. Figueras,Donald McGarey

doi:10.3389/fmicb.2016.01337

Cody R. Rasmussen-Ivey, Mark R. Liles + Show 2 more

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https://doi.org/10.3389/fmicb.2016.01337

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Abstract

The ubiquitous “jack-of-all-trades,” Aeromonas hydrophila, is a freshwater, Gram-negative bacterial pathogen under revision in regard to its phylogenetic and functional affiliation with other aeromonads. While virulence factors are expectedly diverse across A. hydrophila strains and closely related species, our mechanistic knowledge of the vast majority of these factors is based on the molecular characterization of the strains A. hydrophila AH-3 and SSU, which were reclassified as A. piscicola AH-3 in 2009 and A. dhakensis SSU in 2013. Individually, these reclassifications raise important questions involving the applicability of previous research on A. hydrophila virulence mechanisms; however, this issue is exacerbated by a lack of genomic data on other research strains. Collectively, these changes represent a fundamental gap in the literature on A. hydrophila and confirm the necessity of biochemical, molecular, and morphological techniques in the classification of research strains that are used as a foundation for future research. This review revisits what is known about virulence in A. hydrophila and the feasibility of using comparative genomics in light of this phylogenetic revision. Conflicting data between virulence factors, secretion systems, quorum sensing, and their effect on A. hydrophila pathogenicity appears to be an artifact of inappropriate taxonomic comparisons and/or be due to the fact that these properties are strain-specific. This review audits emerging data on dominant virulence factors that are present in both A. dhakensis and A. hydrophila in order to synthesize existing data with the aim of locating where future research is needed.

Highlights

The ubiquitous bacterium Aeromonas hydrophila is a freshwater, facultatively anaerobic, chemoorganoheterotroph (Garrity et al, 2006) and the etiologic agent of disease in amphibians, birds, fishes, mammals, and reptiles, with the most common forms of disease being gastroenteritis, septicemia, and necrotizing fasciitis (Cipriano et al, 1984; Figueras et al, 2007; Monaghan et al, 2008; Janda and Abbott, 2010)
In 2013, A. hydrophila subsp. dhakensis was recognized to be synonymous to A. aquariorum and both were combined under the name A. dhakensis, a species that is functionally divergent from A. hydrophila, based on multilocus phylogenetic analyses and phenotypic characteristics (Beaz-Hidalgo et al, 2013)
Given the turbulent nature of classification within Aeromonas spp., this review aims to clarify which virulence factors have been characterized within current members of A. hydrophila (Supplementary Table S1) by auditing the body of knowledge on the molecular understanding of these genes so that future research can progress from a more solid foundation

Summary

Introduction

The ubiquitous bacterium Aeromonas hydrophila is a freshwater, facultatively anaerobic, chemoorganoheterotroph (Garrity et al, 2006) and the etiologic agent of disease in amphibians, birds, fishes, mammals, and reptiles, with the most common forms of disease being gastroenteritis, septicemia, and necrotizing fasciitis (Cipriano et al, 1984; Figueras et al, 2007; Monaghan et al, 2008; Janda and Abbott, 2010). The majority of experimental studies on identifying virulence determinants in Aeromonas spp. have been performed in the strain A. hydrophila SSU, which was later recognized to be affiliated with A. dhakensis on the basis of ANI and phylogeny comparisons (Grim et al, 2014). Adding confusion to this complexity, the literature on A. hydrophila is riddled with conflicting reports on the molecular determinants of virulence attributed to this species because of changes in classification and problems stemming from misidentification (Colston et al, 2014; Beaz-Hidalgo et al, 2015). Given the turbulent nature of classification within Aeromonas spp., this review aims to clarify which virulence factors have been characterized within current members of A. hydrophila (Supplementary Table S1) by auditing the body of knowledge on the molecular understanding of these genes so that future research can progress from a more solid foundation

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