DAO 46:147-152 (2001)  -  doi:10.3354/dao046147

Detection of ŒCandidatus Xenohaliotis californiensis¹ (Rickettsiales-like prokaryote) inclusions in tissue squashes of abalone (Haliotis spp.) gastrointestinal epithelium using a nucleic acid fluorochrome

James D. Moore1,2,*, Gary N. Cherr2,3, Carolyn S. Friedman1,4

1California Department of Fish and Game,
2University of California Bodega Marine Laboratory, 2099 Westside Road, Bodega Bay, California 94923, USA
3Department of Environmental Toxicology, and
4Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, California 95616, USA

ABSTRACT: Rickettsiales-like prokaryotes appear to be etiologic agents of a number of newly described diseases of fish and shellfish. ŒCandidatus Xenohaliotis californiensis¹ is a Rickettsiales-like prokaryote responsible for withering syndrome, a fatal disease of wild and farmed Eastern Pacific abalone, Haliotis spp. The bacterium proliferates in gastrointestinal epithelial cells, forming large intracytoplasmic inclusions. We describe a method of rapidly detecting and assessing the intensity of ŒCandidatus Xenohaliotis californiensis¹ infections in abalone gastrointestinal tissue using the nucleic acid-specific fluorochrome Hoechst 33258. In excised tissue pieces dried onto slides, rehydrated in the Hoechst stain and viewed with ultraviolet light, the large bacterial inclusions were strongly fluorescent and could be easily distinguished from smaller host cell nuclei. This provided a rapid, inexpensive alternative to paraffin section microscopy or molecular techniques, allowing detection of the pathogen within minutes of tissue excision. Comparison of the fluorochrome method with conventional histological analysis for the ability to detect inclusions in 109 samples was 90% accurate, with discrepancies due to false negative diagnosis of low-level infections. An alternative nucleic acid-specific fluorochrome, propidium iodide, showed a staining pattern identical to that of Hoechst 33258. These methods should prove useful for the rapid detection of inclusion-forming Rickettsiales-like prokaryotes in tissues from many host species.

KEY WORDS: ŒCandidatus Xenohaliotis californiensis¹ · Nucleic acid · Rickettsiales · Abalone

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