Taxonomy of bacterial fish pathogens

Abstract

Bacterial taxonomy has progressed from reliance on highly artificial culture-dependent techniques involving the study of phenotype (including morphological, biochemical and physiological data) to the modern applications of molecular biology, most recently 16S rRNA gene sequencing, which gives an insight into evolutionary pathways (= phylogenetics). The latter is applicable to culture-independent approaches, and has led directly to the recognition of new uncultured bacterial groups, i.e. "Candidatus", which have been associated as the cause of some fish diseases, including rainbow trout summer enteritic syndrome. One immediate benefit is that 16S rRNA gene sequencing has led to increased confidence in the accuracy of names allocated to bacterial pathogens. This is in marked contrast to the previous dominance of phenotyping, and identifications, which have been subsequently challenged in the light of 16S rRNA gene sequencing. To date, there has been some fluidity over the names of bacterial fish pathogens, with some, for example Vibrio anguillarum, being divided into two separate entities (V. anguillarum and V. ordalii). Others have been combined, for example V. carchariae, V. harveyi and V. trachuri as V. harveyi. Confusion may result with some organisms recognized by more than one name; V. anguillarum was reclassified as Beneckea and Listonella, with Vibrio and Listonella persisting in the scientific literature. Notwithstanding, modern methods have permitted real progress in the understanding of the taxonomic relationships of many bacterial fish pathogens.

Characterization and antimicrobial susceptibility of motile aeromonads isolated from freshwater ornamental fish showing signs of septicaemia

“…Aeromonas hydrophila is the most cited motile Aeromonas species classically linked to MAS in freshwater fish (Hettiarachchi & Cheong 1994, Nielsen et al 2001, Austin 2011. In contrast, we found A. veronii (79.2%) to be the predominant species which is in agreement with others who reported the dominance of A. veronii among fish pathogenic aeromonad isolates following molecular identification (Sreedharan et al 2011, 2013, Hu et al 2012, Yi et al 2013.…”

“…Historically, Aeromonas hydro phila has gained much attention as the most common fish pathogenic motile Aeromonas species, but other Aeromonas species may also play an important role in fish pathology that needs to be explored (BeazHidalgo & Figueras 2012). Well-documented discrepancies in phenotypic identification of Aero monas at the species level (Koziń ska 2007, Beaz-Hidalgo et al 2010) may have impacted the species designations of the fish pathogenic aeromonads identified to date (Austin 2011), but the use of molecular approaches, such as the sequencing of rpoD and gyrB genes (Yáñez et al 2003, Soler et al 2004, has led to increased accuracy of Aeromonas species identification.…”

Aeromonas salmonicida isolated from wild and farmed fish and invertebrates in Oman

“…Notwithstanding, some isolates did lead to the development of small haemorrhages in/on the internal organs, as reported previously (Austin and Adams 1996). In this respect, it is worthwhile to consider the comments of Austin and Austin (1993) and Austin (2011), who considered that loss of virulence might well reflect the effects of storage, i.e. the transition to what are effectively laboratory cultures, and the inability to replicate conditions of the initial disease, which led to the recovery of the cultures.…”

Public good dynamics drive evolution of iron acquisition strategies in natural bacterioplankton populations

“…F12 (16,17), Allivibrio fischerii, and Vibrio ordalii. These latter two are known from the literature to be associated with animal hosts (18,19), where iron acquisition is likely a critical factor in colonization (20). For all other sampled populations, the production trait is patchily distributed across the tree, implying that it is frequently gained and lost within lineages.…”