First isolation of Vibrio tapetis and an atypical strain of Aeromonas salmonicida from skin ulcerations in common dab (Limanda limanda) in the North Sea

Abstract

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.

Biogeography of the fish pathogen Aeromonas salmonicida inferred by vapA genotyping

“…2017; Vercauteren et al . 2017). In the present study, we compared vapA sequences from an extended A. salmonicida collection (675 isolates) of worldwide origin, recovered over six decades from a broad range of fish hosts.…”

Pinpointing the role of Aeromonas salmonicida in the development of skin ulcerations in common dab (Limanda limanda)

“…The bacterial strain (original isolate—2CK) was isolated from an active skin ulceration in a common dab caught in the BNS. The isolate was identified as A. salmonicida using 16S rRNA gene sequencing, and subsequent vap A gene sequencing confirmed the presence of A‐layer type 15 (Vercauteren et al, ). According to the traditional nomenclature, the isolate was an ‘atypical’ strain; however, it did not belong to any of validly described subspecies.…”

“…Commonly reported clinical signs linked to A. salmonicida infections include skin ulcerations, furuncle formation, lethargy, loss of orientation, haemorrhages in various internal organs, splenomegaly, myocarditis, liquefactive necrosis of the kidney and mortality (Austin & Austin, ; Wiklund & Dalsgaard, ). Recently, A. salmonicida was isolated from skin ulcerations in common dab in the BNS (Vercauteren et al, ). Various subtypes of the pathogen have been described and may be discerned based on the sequence of the virulence array protein gene ( vapA ), producing the crystalline, outer membrane protein (A layer; Gulla, Lund, Kristoffersen, Sørum, & Colquhoun, ).…”

“…Various subtypes of the pathogen have been described and may be discerned based on the sequence of the virulence array protein gene ( vapA ), producing the crystalline, outer membrane protein (A layer; Gulla, Lund, Kristoffersen, Sørum, & Colquhoun, ). The isolates recovered from common dab in the BNS could all be assigned to the distinct A‐layer type 15 (Vercauteren et al, ), a type which has subsequently been identified as exclusively associated with northern European specimens of this fish species (Gulla et al, ).…”

Direct mortality among demersal fish and benthic organisms in the wake of pulse trawling

“…For dab we observed 'wounds' in all treatments with incidences ranging from 9.5 to 25% in the sampled fish. Without exception these wounds were skin ulcerations which are prevalent in wild common dab (Vercauteren et. al., 2018) which we consider to be unrelated to the current experimental treatments.…”