Kocuria SM1 controls vibriosis in rainbow trout (Oncorhynchus mykiss, Walbaum)

Aims: To develop probiotics for the control of vibriosis caused by Vibrio anguillarum and Vibrio ordalii in finfish. Methods and Results: Kocuria SM1, isolated from the digestive tract of rainbow trout, was administered orally to rainbow trout (Oncorhynchus mykiss) for 2 weeks at a dose equivalent to c. 10⁸ cells per g of feed and then challenged intraperitoneally with V. anguillarum and V. ordalii. Use of SM1 led to a reduction in mortalities to 15-20% compared to 74-80% mortalities in the controls. SM1 stimulated both cellular and humoral immune responses in rainbow trout, by elevation of leucocytes (5·5 ± 0·8 × 10⁶ ml ^-1 from 3·7 ± 0·8 × 10⁶ ml ^-1), erythrocytes (1·2 ± 0·1 × 10 ⁸ ml^-1 from 0·8 ± 0·1 × 10 ⁸ ml^-1), protein (23 ± 4·4 mg ml ^-1 from 16 ± 1·3 mg ml^-1), globulin (15·7 ± 0·2 mg ml^-1 from 9·9 ± 0·1 mg ml^-1) and albumin (7·3 ± 0·2 mg ml^-1 from 6·1 ± 0·1 mg ml^-1) levels, upregulation of respiratory burst (0·05 ± 0·01 from 0·02 ± 0·01), complement (56 ± 7·2 units ml^-1 from 40 ± 8·0 units ml^-1), lysozyme (920 ± 128·8 units ml^-1 from 760 ± 115·3 units ml^-1) and bacterial killing activities. Conclusions: Kocuria SM1 successfully controlled vibriosis in rainbow trout, and the mode of action reflected stimulation of the host innate immune system. Significance and Impact of the Study: Probiotics can contribute a significant role in fish disease control strategies, and their use may replace some of the inhibitory chemicals currently used in fish farms. © 2009 The Society for Applied Microbiology.