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 × 10⁸ ml⁻¹ from 0·8 ± 0·1 × 10⁸ 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. [ABSTRACT FROM AUTHOR]