Virulence properties of Moritella viscosa extracellular products

Abstract

Moritella viscosa is the causative agent of winter ulcer disease of marine fish. Knowledge of its pathogenicity is limited and there are no reports comparing the virulence properties of a collection of bacterial isolates. The in vivo and in vitro virulence of the extracellular products (ECP) of 22 M. viscosa isolates was screened. Two non-virulent Canadian isolates and a Norwegian isolate with reduced virulence produced non-lethal ECP. Correlation was obtained between cytotoxin and haemolysin production of M. viscosa. Isolates from salmon produced ECP with lower cytotoxic and haemolytic activities than ECP of isolates originating from other hosts. Correlation was not found between lethality of ECPs in salmon and cytotoxic or haemolytic activities. All isolates secreted esterases and a metallopeptidase (MvP1), degraded starch and produced siderophores. Variable levels of ECP protein concentration, different enzymatic activities and siderophore production could not explain differences in virulence. The results show that virulent M. viscosa isolates secrete a lethal toxic factor of unknown nature and that cytotoxin production may reflect host adaptation. Cell-culture models may not be optimal for determining the virulence of M. viscosa, as no association between cytotoxicity and bacterial virulence was obtained. Non-virulent strains may be useful in future research on M. viscosa virulence, as construction of mutants has not been successful.

Pan genome and CRISPR analyses of the bacterial fish pathogen Moritella viscosa

“…The isolates include both typical and variant M. viscosa , which were categorized as per standard biochemical and phenotypic methods as well as sequence analysis [2, 5, 8, 21]. The complete genome of the virulent M. viscosa MV 0609139 [22, 23] was used as reference.…”

An Overview of the Immunological Defenses in Fish Skin

“…Ulcerative lesions are likely to be initiated by a series of factors that lead ultimately to a breach of the normal barrier function of the skin (reviewed in [264]). In this sense, the bacteria Moritella viscosa is considered the agent causing winter ulcer diseases characterized by extensive and chronic ulceration of the skin and septicaemia [269][270][271][272]. Recently it has been demonstrated that this bacteria (but not A. wodanis) affected or inhibited the epidermal regeneration abilities of keratocytes [273].…”

The environmental and host‐associated bacterial microbiota of Arctic seawater‐farmed Atlantic salmon with ulcerative disorders

“…). Little is known of M. viscosa virulence, but its extracellular products (ECPs) are both cytotoxic to fish cells and lethal to Atlantic salmon (Bjornsdottir, Gudmundsdottir & Gudmundsdottir ). It is further anticipated that environmental factors such as temperature and the status of skin health are important factors for susceptibility to infections (Tunsjø et al .…”