Recently,
Vibrio tapetis
was isolated for the first time from skin ulcerations in wild-caught common dab (
Limanda limanda
). To further examine its role in the development of these skin lesions, an in vivo experiment was performed. The significance of the skin barrier and in addition the difference between pigmented and non-pigmented side were investigated. Hence, the skin of common dab was treated in three different ways on both the pigmented and non-pigmented side. On a first “treatment zone”, the scales and overlying epidermal tissue were removed whereas in a second zone only the mucus was discarded. The third zone served as a non-treated zone. Thereafter, fish were challenged with
V. tapetis
. The control group was sham treated. Mortality, clinical signs, severity and size of the developing lesions were recorded. All animals were sacrificed and sampled 21 days post-inoculation. Significantly more fish of the group challenged with
V. tapetis
died compared to the control group with the highest incidence occurring 4 days post-inoculation. Fish challenged with
V. tapetis
developed more severe skin ulcerations. In zones where scales and epidermal tissue were removed, the ulcerations were more severe compared to zones where only mucus was eliminated. Ulcerations occurred more frequently, were more severe and larger on the pigmented side. Our data represents prove of
V. tapetis
as causative agent of ulcerative skin lesions although prior damage of the skin seems to be a major contributing factor. Furthermore, the pigmented side seemed predisposed to the development of skin ulcerations.
Electronic supplementary material
The online version of this article (10.1186/s13567-019-0659-6) contains supplementary material, which is available to authorized users.
Skin ulcerations rank amongst the most prevalent lesions affecting wild common dab (Limanda limanda) with an increase in prevalence of up to 3.5% in the Belgian part of the North Sea. A complex aetiology of these ulcerations is suspected, and many questions remain on the exact factors contributing to these lesions. To construct the aetiological spectrum of skin ulcerations in flatfish, a one-day monitoring campaign was undertaken in the North Sea. Fifteen fish presented with one or more ulcerations on the pigmented and/or non-pigmented side. Pathological features revealed various stages of ulcerations with loss of epidermal and dermal tissue, inflammatory infiltrates and degeneration of the myofibers bordering the ulceration, albeit in varying degrees. Upon bacteriological examination, pure cultures of Vibrio tapetis were retrieved in high numbers from five fish and of Aeromonas salmonicida in one fish. The V. tapetis isolates showed cross-reactivity with the sera against the representative strain of serotype O2 originating form a carpet-shell clam (Ruditapes descussatus). Moreover, the A. salmonicida isolates displayed a previously undescribed vapA gene sequence (A-layer type) with possible specificity towards common dab. Further research is necessary to pinpoint the exact role of these agents in the development of skin ulcerations in common dab.
A recently described typing system based on sequence variation in the virulence array protein (
vapA
) gene, encoding the A-layer surface protein array, allows unambiguous subtyping of
Aeromonas salmonicida
. In the present study, we compile A-layer typing results from a total of 675
A. salmonicida
isolates, recovered over a 59-year period from 50 different fish species in 26 countries. Nine novel A-layer types (15–23) are identified, several of which display a strong predilection towards certain fish hosts, including e.g. Cyprinidae and Pleuronectidae species. Moreover, we find indications that anthropogenic transport of live fish may have aided the near global dissemination of two cyprinid-associated A-layer types. Comparison of whole genome phylogeny and A-layer typing for a subset of strains further resulted in compatible tree topologies, indicating the utility of
vapA
as a phylogenetic as well as an epizootiological marker in
A. salmonicida
. A Microreact project (
microreact.org/project/r1pcOAx9m
) has been created, allowing public access to the
vapA
analyses and relevant metadata. In sum, the results generated provide valuable insights into the global population structure of
A. salmonicida
, particularly in relation to its piscine host spectrum and the geographic distribution of these hosts.
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