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Appears in Collections:Aquaculture Journal Articles
Peer Review Status: Refereed
Title: A Polyphasic Approach for Phenotypic and Genetic Characterization of the Fastidious Aquatic Pathogen Francisella noatunensis subsp. orientalis
Author(s): Ramirez-Paredes, Jose
Thompson, Kim D
Metselaar, Matthijs
Shahin, Khalid
Soto, Esteban
Richards, Randolph
Penman, David
Colquhoun, Duncan J
Adams, Alexandra
Keywords: tilapia diseases
Francisellosis in tilapia
Francisella noatunensis subsp. orientalis
Fno antimicrobial resistance
Francisella characterization
Issue Date: 12-Dec-2017
Citation: Ramirez-Paredes J, Thompson KD, Metselaar M, Shahin K, Soto E, Richards R, Penman D, Colquhoun DJ & Adams A (2017) A Polyphasic Approach for Phenotypic and Genetic Characterization of the Fastidious Aquatic Pathogen Francisella noatunensis subsp. orientalis, Frontiers in Microbiology, 8, Art. No.: 2324.
Abstract: Francisella noatunensis subsp. orientalis (Fno) is the causative agent of piscine francisellosis, an emerging infectious disease in Asia and Latin America. In this study two outbreaks of francisellosis were diagnosed in the UK on the basis of histopathology, electron microscopy, PCR, bacterial isolation and fulfilment of Koch’s postulates. Furthermore, a phenotypic fingerprint based on biochemical analyses, metabolic activity, chemotaxonomic composition and antimicrobial assays was generated for the novel isolates, the Fno type strain Ehime-1 from Asia and other Fno from Latin America. The genetic relatedness between the novel Fno and other Francisellaceae species was investigated by sequencing and comparing 8 housekeeping genes and the 16S rRNA-ITS-23S rRNA sequence. The phenotypic profiling indicated a high degree of similarity between the Fno taxon as all were able to metabolise dextrin, N-acetyl-D glucosamine, D-fructose, α-D-glucose, D-mannose, methyl pyruvate, acetic acid, α-keto butyric acid, L-alaninamide, L-alanine, L-alanylglycine, L-asparagine, L-glutamic acid, L-proline, L-serine, L-threonine, inosine, uridine, glycerol, D L-α-glycerol phosphate, glucose-1-phosphate and glucose-6-phosphate. The chemotaxonomic analyses indicated that 24:1 (20.3%), 18:1n-9 (16.9%), 24:0 (13.1%) 14:0 (10.9%), 22:0 (7.8%), 16:0 (7.6%) and 18:0 (5.5%) were the predominant structural fatty acids in Fno. The antimicrobial assays showed little variation between the isolates and high susceptibility to enrofloxacin, gentamicin, neomycin, streptomycin, amikacin, ciprofloxacin, gatifloxacin, nitrofurantoin, tobramycin, kanamycin, tetracycline, oxytetracycline, florfenicol, oxolinic acid and streptomycin in all the Fno analysed. In all the phylogenetic trees the Fno strains clustered together in independent branches confirming a high degree of homogeneity. Interestingly in five of the individual trees i.e mutS, putA, rpoB, the concatenated sequence and 16S rRNA-ITS-23S rRNA genes the two Francisella noatunensis ssp. diverged more from each other than from the closely related human pathogen Francisella philomiragia (Fp). The phenotypic and genetic characterisation confirmed the Fno isolates represent a solid phylo-phenetic taxon that in the current context of the genus seems to be misplaced within the species Fn. We propose the use of the present polyphasic approach in future studies to characterise strains of Fnn and Fp and verify their current taxonomic rank of Fno.
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Rights: © 2017 Ramírez-Paredes, Thompson, Metselaar, Shahin, Soto, Richards, Penman, Colquhoun and Adams. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

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