Carnobacterium maltaromaticum infections in feral Oncorhynchus spp. (Family Salmonidae) in Michigan

Abstract

Members of the genus Oncorhynchus were introduced from the Pacific Northwest to the Laurentian Great Lakes basin and now constitute one of its most commercially and ecologically valuable fisheries. Recently, infections by a group of Gram-positive atypical lactobacilli belonging to the genus Carnobacterium have been detected in feral and captive Oncorhynchus spp. broodstock, some of which were associated with mortalities. Out of 1564 rainbow and steelhead trout (O. mykiss), coho salmon (O. kisutch), and Chinook salmon (O. tshawytscha) that were bacteriologically examined, 57 Carnobacterium spp. isolates were recovered from the kidneys, spleen, swimbladder, and/or external ulcerations of 51 infected fish. Phenotypic and biochemical characterization, as well as partial 16S rDNA sequencing and phylogenetic analyses of 30 representative isolates identified 29 as Carnobacterium maltaromaticum and 1 as C. divergens, though some phenotypic and genotypic heterogeneity was observed. Infections with C. maltaromaticum were associated with signitures typical of pseudokidney disease, but on occasion were also observed in fish displaying the gross and histopathological changes characteristic of nephrocalcinosis. While C. maltaromaticum infections were found to be widespread in both feral and farmed spawning populations of Oncorhynchus spp. residing within the Great Lakes basin, infection prevalence varied significantly according to fish species and strain, gender, and across time, but not by sampling location according to logistic regression analysis. The findings of this study further underscore the presence of phenotypic variations among Carnobacterium maltaromaticum strains that necessitate genotypic analysis to achieve definitive identification.

Diversity of Fish‐Associated Flavobacteria of Michigan

“…Fish either were delivered to the laboratory alive and then euthanized with an overdose of tricaine methanesulfonate Argent Chemical Laboratories,Redmond,Washington) or were euthanized by Michigan Department of Natural Resources (MDNR) personnel and sampled on-site. Tissues for bacterial culture were collected as described by Loch et al (2011), with the exception that 1-µL loops were used for fish ≤6 cm in length and 10-µL loops were used for fish >6 cm in length. Kidney or gill tissues (or both) for bacterial isolation were collected during fish health surveillance; other tissues (e.g., gills, fins, swim bladder fluid, external ulcers, or combination of these) were also bacteriologically analyzed when disease signs were observed.…”

“…Figure 2). Eight isolates belonging to cluster VII (S40, S29, S35, S34, S38, S37, S31, and S41) were all recovered from the brains of hatchery-reared Coho Salmon fry undergoing a single mortality episode (Faisal et al 2011). Isolates belonging to cluster VIII were recovered exclusively from hatchery-reared Brook Trout and Rainbow Trout, while the other two clusters (VI and VII) were recovered from both wild and hatchery-reared fish (Supp.…”

“…isolates that belonged to cluster XII were primarily recovered from the gills of wild fish that were sampled during fish health surveillance (Supp . Table 1); however, isolate S43 was recovered from the brain of a hatchery-reared Coho Salmon fry during a mortality event (Faisal et al 2011). Interestingly, of the wild fish from which the cluster XII isolates were recovered, the majority were collected in (1) the creek supplying water to the hatchery where 154 LOCH ET AL.…”

“…In Michigan and its associated state fish hatcheries, Flavobacterium spp. have been associated with more fish mortality than all other fish pathogens combined (Faisal and Hnath 2005;Faisal et al 2011). Flavobacterial isolates have ranged from the most common three Flavobacterium spp.…”

Scientific Opinion on the maintenance of the list of QPS biological agents intentionally added to food and feed (2012 update)

“…Carnobacterium maltaromaticum is known as a fish pathogen (Loch et al, 2011;Schaffer et al, 2012). Few reports of Carnobacterium species have shown isolation from human pus or from human blood culture (Hoenigl et al, 2010).…”