Abstract
Aeromonas hydrophila is still the major problem of the decline in tilapia production. The use of probiotics as disease prevention agents is one of alternative strategy. One of probiotic candidate that has been molecularly identified through 16s RNA was Bacillus methylotrophicus that was known as a bacteria that produces cyclic lipopeptides belonging to surfactin, iturin, and fengycin families. The aim of this research was to study B.methylotrophicus in inhibiting A.hydrophila in Oreochromis niloticus culture. This research consisted of in vitro and in vivo test that used experiment method with completely randomized design, 4 treatments (density of 1 fish/l) and 3 replications. The treatments were various mixture concentration of A.hydrophila at 102 CFU ml-1 with bacterial B.methylotrophicus (a) 0, (b) 107, (c) 108, (d) 109 CFU ml-1. Experimental animals used 120 fish at average weight of 13,8±1,6 g. Based on the in vitro test, B.methylotrophicus able to inhibit A.hydrophila categorized as bactericidal antibiotic and the most powerful concentration was 109 CFU ml-1 with clear zone of 24,9±4,2 mm. In vivo test did not significantly effect on survival rate, could slow down the growth of A. hydrophila, and had effect on dynamics of leukocytes, erythrocytes, hemoglobin, hematocrit value. Treatment D showed the highest survival rate (56.7%), followed by C (50,00%), B (43,33%), and A (30,00%). The value of leukocytes, erythrocytes, hemoglobin, hematocrit were 66.300–208.700 cells/mm3, 0,3–2,17x106 cells/mm3, 21,8-32,7%, 3,1-7,4 g/dl, respectively. The total bacteria viable count (TBC) in the water and A.hydrophila during treatment were 1,66x1011–1,25x1017 CFU ml-1 and 3,3x104– 1,7x107 CFU ml-1. This results showed that B.methylotrophicus could inhibit growth of A.hydrophila in in vitro, and able to increase the SR until 26, 7% in in vivo test.
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