Proteobacteria Associated with Epitheliocystis-Like Inclusions in Two Captive-Born Bonnethead Sharks (Sphyrna tiburo)
Abstract
Epitheliocystis is a condition affecting gills and skin of teleost fish.1 It refers to basophilic cytoplasmic bacterial "inclusions" identified in the gills.1-4 Lesions consistent with epitheliocystis in elasmobranchs have been reported in hammerhead sharks (Sphyrna spp.), spotted eagle rays (Aetobatus narinari), spiny dogfish (Squalus acanthias), smooth dogfish (Mustelus canis), and a leopard shark (Triakis semifasciata).5-8 Lesions have been historically associated with Chlamydiales species and pan-chlamydial primers have been successfully used to obtain sequence data for a spotted eagle ray and a leopard shark.6,8,9 Recently, advanced diagnostic techniques and molecular analysis have suggested the lesions are actually associated with proteobacteria.2,3 Inclusions morphologically similar to epitheliocystis were found in gills of two captive-born, wild-conceived, bonnethead shark (Sphyrna tiburo) pups. Histopathology of gills revealed typical spherical, granular, basophilic inclusions containing fine filamentous bacterial rods within epithelial cells arising from the lamellae. The organisms are gram negative, and highlighted with Giemsa and Macchiavello stains, but do not stain with periodic acid-Schiff. Immunohistochemistry was performed using monoclonal mouse and polyclonal rabbit anti-chlamydial antibodies, showing strong positive staining with the polyclonal antibody, but not with the monoclonal product. Polymerase chain reactions (PCR) and Sanger sequencing were performed on samples from one pup. Initial PCR with pan-Chlamydiales 16S rRNA gene primers and resultant molecular sequence data support findings that epitheliocystis could be caused by unclassified proteobacteria species. Two adult, wild-caught bonnethead sharks screened for epitheliocystis-like inclusions revealed a similar inclusion indicating that this condition occurs in free-ranging populations.
Acknowledgements
The authors thank Heather Broadhurst, Hap Fatzinger, Kent Passingham, Emily Peele, and Clint Taylor for their support of this project.
* Presenting author
+ Student presenter
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