EFFICACY OF CONVENTIONAL DISINFECTANTS ON ISOLATED STREPTOCOCCUS INIAE FROM DISEASED RAINBOW TROUT IN LABORATORY AND CULTURE TANK CONDITIONS

The efficacy of different disinfectants (formalin, acetic acid, citric acid, chlorhexidine, sodium iodide, potassium permanganate, sodium hypochlorite and cetrimide-c) was examined on Streptococcus iniae, isolated from diseased fish of Fars province over the years 2002- 2004. In laboratory condition, minimum bactericidal concentration of disinfectants after 15, 30, 45 and 60 minutes were evaluated. Disinfectants were also tested under natural conditions with addition of a known concentration of bacterial suspension into water. An effective concentration of each disinfectant that had been determined in the first part of this study was added to the culture tanks and water samples were collected after 15, 30, 45 and 60 minutes to evaluate streptococcus isolation. A 3-5ppm concentration of chlorhexidine and sodium hypochlorite were powerful disinfectants against Streptococcus iniae. Acetic acid and citric acid were efficient in a concentration ranging between 350-500ppm showing very weak disinfectant activity against Streptococcus iniae. Results of tank tests showed that a bio-film is formed in the tanks may have significant effect on lowering the efficiency of disinfectants, thus most disinfectants were only effective at a higher concentration. Generally, sodium iodide and sodium hypochlorite were more efficient against Streptococcus iniae in tank condition than other disinfectants.