Submitted to: Journal of Aquatic Animal Health
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/27/2000
Publication Date: 12/1/2000
Citation: MITCHELL, A.J., GOODWIN, A.E. THE ISOLATION OF EDWARDSIELLA ICTALUARI WITH LIMITED TOLERANCE FOR AEROBIC GROWTH FROM CHANNEL CATFISH.. JOURNAL OF AQUATIC ANIMAL HEALTH. 2000. v.12. p.297-300. Interpretive Summary: Edwardsiella ictaluri is a common bacterial pathogen of channel catfish. This bacterium is normally grown without special incubation techniques. A strain of this bacterium has been isolated that grows initially only in the absence of oxygen or under anaerobic conditions. Once grown under anaerobic conditions the bacterium will grow, although only slightly, in the presence of oxygen when transferred to new growth plates. Catfish from which this bacterium has been isolated have deep brown sores (sometimes the underlying bone is exposed) with no redness (hemorrhage or inflammation) on the edges. Although the sores are not necessarily caused by the bacterium, there is a strong association between the bacteria and the presence of the sores. This study raises questions about the possible presence of other bacteria in fish not found because anaerobic isolation methods are rarely used in diagnostic procedures.
Technical Abstract: Several cases of channel catfish with deep necrotic lesions were submitted to the Stuttgart diagnostic laboratory from 1982 through 1997. Lesions covered an area of several cm2 and were located on the head or sides of the fish. The lesions had well defined edges with an abrupt transition to apparently normal tissue and were frequently deep enough to expose bone. Cases usually occurred in food-sized catfish from May to early July and mortalities lasted several weeks killing less than 10% of the fish. Bacterial isolates from these fish initially grew on TSA agar with blood only under anaerobic conditions, but upon passage a limited aerobic growth was observed. In thioglycolate broth the passaged isolates had growth characteristics of bacteria with a limited tolerance for oxygen. Isolate S97-133, from May 1997, was identified as Edwardsiella ictaluri by the National Veterinary Services Laboratories, Ames, Iowa. The S97-133 isolate and three others from 1994 were also definitively identified as E. ictaluri using the monoclonal immuno dot blot technique. There is a strong association between the presence of these lesions and the presence of an E. ictaluri with limited tolerance for oxygen.