Isolation of Aeromonas salmonicida subspecies salmonicida from Lake Whitefish (Coregonus clupeaformis) inhabiting Lakes Michigan and Huron Thomas P. Loch a , Mohamed Faisal a,b, ⁎ a Department of Pathobiology and Diagnostic Investigation, College of Veterinary Medicine, Michigan State University, S-110 Plant Biology Building, East Lansing, MI 48824, USA b Department of Fisheries and Wildlife, College of Agriculture and Natural Resources, Michigan State University, S-110 Plant Biology Building, East Lansing, MI 48824, USA abstract article info Article history: Received 30 December 2008 Accepted 10 June 2009 Communicated by Travis Brenden Index words: Lake whitefish Aeromonas salmonicida subspecies salmonicida Great Lakes Herein we describe the first report of Aeromonas salmonicida subspecies salmonicida infections in lake whitefish (Coregonus clupeaformis) collected from four sites in lakes Michigan and Huron, Michigan, USA. The bacterium was isolated from the kidneys of four out of 1286 lake whitefish that were tested over a three-year period. The four isolates were phenotypically similar to one another and exhibited the morphological, colonial, and biochemical traits typical of A. salmonicida subspecies salmonicida. Amplification of 16S rRNA genes specific to A. salmonicida subspecies salmonicida via polymerase chain reaction and subsequent gel electrophoresis analyses confirmed the identity of the four lake whitefish isolates. Clinical signs associated with infection included extensive external hemorrhaging, exophthalmia, splenomegaly, splenic and renal congestion, fibrinous adhesions of the spleen and liver, and hemorrhagic enteritis. Histopathological examination of infected fish revealed multi-focal hemorrhage and infiltration of lymphocytes and histiocytes in subdermal adipose tissues and musculature. A low infection incidence of A. salmonicida salmonicida in Great Lakes lake whitefish does not preclude the fact that overt signs of disease were observed in infected individuals and that lake whitefish may act as a reservoir for this bacterium that is highly pathogenic to numerous fish species. © 2009 Elsevier B.V. All rights reserved. Introduction There is increasing concern regarding the role diseases may play in the observed decline of economically and ecologically important fish species in the Laurentian Great Lakes (Faisal and Hnath 2005). Currently, lake whitefish is the most commercially valuable fish species within GLB (Bronte et al. 2003; Hoyle 2005; Schneeberger et al. 2005; Cook et al. 2005; Mohr and Ebener 2005) after recovering from devastating declines associated with overexploitation and inter- actions with invasive species (Ebener 1997; Mohr and Nalepa 2005). However, within several of the Great Lakes, lake whitefish have recently suffered declines in abundance, condition, and size at age (Hoyle et al. 1999; Pothoven et al. 2001; Madenjian et al. 2002; Mohr and Ebener 2005). Unfortunately, there is a severe gap of knowledge regarding pathogens that affect lake whitefish in the Great Lakes basin. This problem is compounded by the fact that Coregonus clupeaformis is not propagated artificially; therefore, information on susceptibility of this important species to microbial pathogens can only be obtained from studying wild lake whitefish stocks. Herein, we report on infections of lake whitefish with the fish-pathogenic Gram- negative bacterium, Aeromonas salmonicida. A. salmonicida causes ecologic and economic devastation in wild and farmed fishes worldwide (Austin and Adams 1996) and in the USA, this pathogenic bacterium is threatening the conservation and restoration program of some salmonid fish species (Cipriano 1997). Currently, five subspecies of A. salmonicida have been recognized: salmonicida, achromogenes, masoucida, smithia (Holt et al. 2000), and pectinolytica (Pavan et al. 2000). A. salmonicida salmonicida is considered extremely pathogenic to certain salmonid species, causing a septicemic infection known as furunculosis, while other species can serve as asymptomatic carriers (Cipriano and Bullock 2001). A. salmonicida salmonicida has also been recovered from apparently healthy fish and it is believed that these infected individuals act as a reservoir for the bacterium (Hiney et al. 1997). As this is the first record of A. salmonicida infecting lake whitefish, this study was designed to determine the characteristics of the A. salmonicida strains and the tissue alterations associated with these infections in lake whitefish. Materials and methods Fish and sampling Lake whitefish were collected for disease testing from four Great Lakes lake whitefish stocks (∼ 30 fish/site/season) during the period of fall 2003 to summer 2006. The fish were collected from Journal of Great Lakes Research 36 (2010) 13–17 ⁎ Corresponding author. S-110 Plant Biology Building, Michigan State University, East Lansing, MI 48824, USA. Tel.: +1 517 432 8259. E-mail address: Faisal@cvm.msu.edu (M. Faisal). 0380-1330/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jglr.2009.07.002 Contents lists available at ScienceDirect Journal of Great Lakes Research journal homepage: www.elsevier.com/locate/jglr