Inactivation of bacterial fish pathogens by medium- chain lipid molecules (caprylic acid, monocaprylin and sodium caprylate) Anup Kollanoor, Pradeep Vasudevan, Manoj Kumar Mohan Nair,Thomas Hoagland & Kumar Venkitanarayanan Department of Animal Science, University of Connecticut, Storrs, CT, USA Correspondence: K Venkitanarayanan, Department of Animal Science, Unit 4040, University of Connecticut, Storrs, CT 06269, USA. E-mail: kumar.venkitanarayanan@uconn.edu Abstract The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of caprylic acid (CA), monocaprylin (MC, monoglyceride ester of CA) and sodium caprylate (SC) on Edwardsiella ictaluri , E. tarda, Streptococcus iniae and Yersinia ruckeri in Mueller Hinton broth (MHB) were investigated. In addition, the bactericidal kinetics of CA and MC on the aforementioned pathogens in MHB, and that of SC in water, were determined. The MIC of CA and SC on E. ictaluri , E. tarda, S . iniae and Y . ruckeri were 7.5 and 50 mM, 7.5 and 50mM, 10 and 25 mM, and 7.5 and 25mM respectively. For MC, the MIC was in be- tween 2.5 and 5mM for all the pathogens. The MBC of CA, MC and SC on E. ictaluri , E. tarda, S . iniae and Y . ruckeri were 10, 5 and 100 mM; 10, 5 and 100 mM; 15, 5 and 75 mM; and 10, 5 and 75mM respectively. The three lipid molecules exerted a substantial antimicro- bial e¡ect on the ¢sh pathogens studied. The results indicate that CA and its derivatives could potentially be used for treating and controlling bacterial ¢sh dis- eases, but extensive validation studies in ¢sh are needed before recommending their usage. Keywords: caprylic acid, monocaprylin, sodium caprylate, aquaculture Introduction Aquaculture is one of the fastest growing food-pro- ducing sectors in the world, with an annual growth rate of approximately10%, as against 2.8% observed in terrestrial farmed meat production (FAO 2002). The Food and Agricultural Organization estimates that as the world population increases, the global sea food demand is expected to grow by 70% in the next 35 years. This situation would require a seven- fold increase in aquaculture production by 2025. However, disease outbreaks a¡ecting various aquatic species constitute a signi¢cant obstacle to the growth of aquaculture industry worldwide, curtailing the production and economic development of the sector (Subasinghe 1997). The industry is frequently en- countered with disease epizootics, and infectious dis- eases account for the single largest cause of economic losses incurred in aquaculture, amounting to approximately $8 billion annually worldwide (Enright 2003). Edwardsiella ictaluri , E. tarda, Strepto- coccus iniae and Yersinia ruckeri are some of the major ¢sh pathogens that pose a signi¢cant threat to the aquaculture industry. Although the value of the US aquaculture production increased to nearly $1 bil- lion in the last two decades (ERS-USDA 2005), dis- eases caused by the aforementioned pathogens result in substantial losses to the industry. Enteric septicaemia in channel cat¢sh ( Ictalurus punctatus ) caused by E. ictaluri is the most signi¢cant disease af- fecting the US cat¢sh industry, resulting in an annual economic loss of US$40^50 million (Yeh, Shoemaker & Klesius 2005). The infection produced by E. ictaluri occurs in acute and chronic forms. In the acute form, death occurs in 4^12 days, whereas the chronic con- dition is characterized by granulomatous menin- goencephalitis and skin lesions (Keskin, Secer, Izgur, Turkyilmaz & Mkakokya 2004). Acute septicaemia generally develops when the water temperature is 22^28 1C. Edwardsiella ictaluri can survive in water Aquaculture Research, 2007, 38, 1293^1300 doi: 10.1111/j.1365-2109.2007.01799.x r 2007 The Authors Journal Compilation r 2007 Blackwell Publishing Ltd 1293