Submitted to: Journal of Aquatic Animal Health
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/27/2000
Publication Date: 12/1/2000
Citation: MITCHELL, A.J., GOODWIN, A.E. THE ISOLATION OF EDWARDSIELLA ICTALURI, WITH A 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: While culturing trunk kidneys from channel catfish Ictalurus punctatus with deep ulcerative lesions, we discovered strains of Edwardsiella ictaluri that could not be isolated under aerobic conditions. Upon passage of these bacterial isolates in an aerobic environment, minimal 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 E. ictaluri by the National Veterinary Services Laboratories (NVSL), 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. A total of eight isolates were obtained from channel catfish over an eight year period. All isolates were obtained during the months of May, June, July and November.