Submitted to: Diseases of Aquatic Organisms
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/11/2005
Publication Date: 3/2/2006
Citation: Panangala, V.S., Shelby, R.A., Shoemaker, C.A., Klesius, P.H., Mitra, A., Morrison, E.E. 2006. Immunofluorescent test for simultaneous detection of Edwardsiella ictaluri and Flavobacterium columnare. Diseases of Aquatic Organisms, 68: 197-207. Interpretive Summary: Enteric septicemia of catfish (ESC) and columnaris disease are two economically important bacterial diseases affecting the aquaculture industry and rapid diagnosis of disease is critical to fish farmers to make important management decisions. A rapid microscopic test using two (red and green) color-labeled-reagents (fluorescent antibodies) were used for simultaneous detection of Edwardsiella ictaluri (green-labeled) and Flavobacterium columnare (red-labeled) in the kidney, nose and brain tissues of diseased fish. The test was compared with the conventional bacteriological culture technique which is the standard for comparison of other test systems for disease diagnosis. The two-color Immunofluorescent antibody test compared favorably in sensitivity (80.7% and 87.2%) and specificity (83.9% and 88.9%) with the standard bacteriological culture technique for diagnosis of the bacterial diseases caused by Edwardsiella ictaluri and Flavobacterium columnare. Thus the two-color Immunofluorescent antibody test will serve as an efficient tool for rapid simultaneous detection of the two bacteria in outbreaks of disease. Conventional bacteriological culture techniques take a minimum of three to four days to arrive at a diagnosis, whereas the Immunofluorescent antibody test could simultaneously detect the presence of Edwardsiella ictaluri and/or Flavobacterium columnare in diseased fish within a significantly shorter period of four to five hours. Rapid diagnosis of disease will save the fish farmers millions of dollars.
Technical Abstract: Enteric septicemia of catfish (ESC) and columnaris disease are two economically important bacterial diseases affecting the aquaculture industry and rapid diagnosis of disease is imperative for making judicious management decisions. A rapid indirect fluorescent antibody (IFA) test with fluorescent conjugated-antibodies having two different spectral properties (Alexa Fluor 488- emitting green fluorescence and Alexa Fluor 594- emitting red fluorescence) was compared with bacteriological culture (gold standard) for simultaneous detection of Edwardsiella ictaluri (EI) and Flavobacterium columnare (FC) in three groups of experimentally infected channel catfish (Ictalurus punctatus Rafinesque) and a fourth group that acquired an aquarium-infection with F. columnare. A total of 303 samples (derived from kidney, brain and nares respectively) from 101 fish were concurrently examined by both tests. Fish in the three experimentally infected groups yielded the bacteria with which they were infected, while the fish in fourth group revealed F. columnare both by culture and IFA test. The IFA test compared favorably in sensitivity (for EI = 80.7%, and for FC = 87.2%) and specificity (for EI = 83.9% and for FC = 88.9%) with the standard bacteriological culture. The positive predictive value (for EI = 96.2% group I ; 90.8% group II; and 93.7% groups I & II combined; for FC = 95.2% group II; and 95.3% groups II, III & IV combined) was high, while the negative predictive value (for EI = 66.7% group I; 31.3% group II, and 59.5% groups I & II combined; for FC = 73.7% group II and 72.7% groups II, III, & IV combined) was relatively low. The IFA test will serve as an efficient tool for rapid simultaneous detection of E. ictaluri and F. columnare in outbreaks of disease.