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. 10(8) 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 x 10(6) ml(-1) from 3.7 +/- 0.8 x 10(6) ml(-1)), erythrocytes (1.2 +/- 0.1 x 10(8) ml(-1) from 0.8 +/- 0.1 x 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.