Carnobacterium maltaromaticum Septicemia in Atlantic Halibut Hippoglossus hippoglossus

 Ashley L. Powell1, Gerry R. Johnson2, Alvin C. Camus1, David B. Groman3

 1Department of Pathology, College of Veterinary Medicine, University of Georgia, Athens, GA, 30605; 2Department of Pathology & Microbiology, Atlantic Veterinary College, University of Prince Edward Island, Charlottetown, PE, C1A 4P3; 3Aquatic Diagnostic Services, Atlantic Veterinary College, University of Prince Edward Island, Charlottetown, PE, C1A 4P3

ABSTRACT

Carnobacterium maltaromaticum is a gram-positive, psychrotropic, lactic-acid-fermenting, facultative anaerobic bacterium found in a variety of terrestrial and aquatic environments. It is used in packaging of frozen fish and meat products due to its ability to inhibit growth of Listeria monocytogenes. This bacterium has been isolated from the gastrointestinal tract of various fish species and has also been used as a probiotic in aquacultured finfish. However, C. maltaromaticum is associated with pseudokidney disease and septicemia in cold-water teleost fish species, including rainbow trout Oncorhynchus mykiss and lake whitefish Coregonus clupeaformis. Furthermore, C. maltaromaticum is associated with meningoencephalitis in stranded salmon sharks Lamna ditropis and most recently in stranded common thresher sharks Alopias vulpinus. In 2020­–2021, an indoor Atlantic halibut Hippoglossus hippoglossus aquaculture facility experienced fifteen sporadic broodstock mortalities. The fish presented with chronic wasting disease, vestibular disease, or acute death. Postmortem examination revealed encephalitis, bronchitis, epicarditis, pneumocystitis, renomegaly, splenomegaly, polyserositis and/or oopharitis. Gram-positive rods were inconsistently found within lesions, consistent with bacterial culture of C. maltaromaticum. While the initially isolated bacteria were susceptible to all tested antimicrobials, the two most recent isolates demonstrated resistance to oxytetracycline and resistance to oxytetracycline, ceftiofur, and sulfamethoxazole trimethoprim, respectively. Three isolates are in the process of genome sequencing to identify virulence factors and to further characterize this bacterium.