A New Multilocus Sequence Typing Scheme and Its Application for the Characterization of Photobacterium damselae subsp. damselae Associated with Mortality in Cetaceans.

Patricia Alba,Luigi Sorbara,Angela Ianzano,Andrea Caprioli,Gianluca Fichi,Fabio Di Nocera,Valentina Donati,Giuliana Terracciano,Cristiano Cocumelli,Antonio Battisti,Francesco Scholl,Alessia Franco

doi:10.3389/fmicb.2016.01656

Abstract

Photobacterium damselae subsp. damselae (PDD) is a known pathogen of fish, humans and marine mammals. In this study, a Multilocus Sequence Typing (MLST) scheme based on six housekeeping genes (glp, gyrB, metG, pnt, pyrC, and toxR) was developed to better understand the PDD population structure and used to type 73 PDD isolates from cetaceans, mainly striped dolphins (Stenella coeruleoalba) involved in mortality episodes, and from a few marine chelonians. Five reference ATCC strains were also included in the study. Typing allowed the discrimination of groups of PDD strains isolated from different host species, at different times and from different geographic areas, suggesting that a clonal PDD group may have spread in the Tyrrhenian sea at the time of an Unusual Mortality Event (UME) among cetaceans, mainly striped dolphins, occurred in early 2013 along the Italian western coasts.

Highlights

Photobacterium damselae subsp. damselae (PDD) is a marine Gram-negative bacterium belonging to the Vibronaceae family, classified in the same species as Photobacterium damselae subsp. piscicida (PDP), the causative agent of pasteurellosis in fish (Andreoni and Magnani, 2014)
Among the different typing methods, a Multilocus Sequence Typing (MLST) scheme using three theoretical housekeeping genes, previously reported to be suitable for phylogenetic studies of Vibrio species, has been already used to study clinical and environmental PDD isolated in Japan (Takahashi et al, 2008) according to the authors themselves, this method presented limitations
In the present study we provided an improved MLST scheme for the genotyping of PDD, a marine bacterial species with a complex genome

Summary

Introduction

Photobacterium damselae subsp. damselae (PDD) is a marine Gram-negative bacterium belonging to the Vibronaceae family, classified in the same species as Photobacterium damselae subsp. piscicida (PDP), the causative agent of pasteurellosis in fish (Andreoni and Magnani, 2014). Damselae (PDD) is a marine Gram-negative bacterium belonging to the Vibronaceae family, classified in the same species as Photobacterium damselae subsp. As other members of the Vibrionaceae family, PDD possess two chromosomes (Okada et al, 2005) and harbor at least two large plasmids (Rivas et al, 2011; Nonaka et al, 2012). Both subspecies share more than 99% of the 16S DNA sequence and show a percentage of DNA-DNA hybridisation greater than 80% (Gauthier et al, 1995). Differential phenotypic tests, only positive for the subsp. damselae include growth at 37◦C, hemolytic activity on sheep blood agar, motility, nitrate reduction, and production of urease and amylase (Thyssen et al, 1998; Rivas et al, 2013a).

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