Inhibitory Mechanism of Robiotic Bacteria on The Growth of Vibrio harveyi in Tiger Shrimp (Penaeus monodon) Larvae

Three probiotics named SKT-b, 1Ub, and Ua had inhibitory activity against the growth of Vibrio harveyi. These strains were mutated by rifampicin resistant. The inhibitory effect of SKT-b,1Ub, and Ua on the growth of V. harveyi was investigated by concomitant incubation of the two bacteria in a culture shrimp larvae. Colony forming unit of V. harveyi, probiotic and total of bacteria in dead, live larvae and water culture was monitored, and survival rate of larvae was investigated. Shrimp inoculated probiotic previously had survival rate higher than control (without probiotic). Number of V. harveyi in treatment without probiotic inoculation also higher compared to treatment with probiotic inoculation in dead, live larvae and water culture. It demonstrated possible inhibition of probiotic bacteria on V. harveyi through competition for adherence sites or nutrition source. Partial sequencing of 16S-rRNA gene showed that 1Ub was similar to Pseudoalteromonas piscicida, whereas SKT-b and Ua were similar to Vibrio alginolyticus. Keywords: probiotic bacteria, inhibitory mechanism, V. harveyi, tiger shrimp ABSTRAK Tiga isolat bakteri probiotik yaitu 1Ub, SKT-b dan Ua telah diuji memiliki aktivitas penghambatan terhadap pertumbuhan V. harveyi secara in vitro. Ketiga isolat ini kemudian diberi penanda resisten rifampisin (RfR) melalui mutasi spontan untuk mempelajari mekanisme penghambatannya pada larva udang windu. Efek penghambatan dari 1Ub, SKT-b dan Ua terhadap pertumbuhan V. harveyi diamati melalui pemberian secara bersamaan antara bakteri probiotik dan V. harveyi tersebut dalam air pemeliharaan larva udang. Jumlah sel bakteri probiotik, V. harveyi dan total bakteri baik pada larva mati, larva hidup dan air pemeliharaan diamati dan kelangsungan hidup larva dihitung. Nilai kelangsungan hidup udang pada perlakuan yang diinokulasi bakteri probiotik lebih tinggi daripada kontrol (tanpa penambahan bakteri probiotik). Jumlah sel V. harveyi pada perlakuan tanpa penambahan probiotik juga lebih tinggi, dibanding pada perlakuan dengan penambahan probiotik baik pada larva mati, larva hidup maupun air media pemeliharaan. Hal ini menunjukkan adanya penghambatan bakteri probiotik terhadap V. harveyi yang kemungkinan melalui kompetisi tempat pelekatan atau sumber nutrisi. Hasil analisis sekuen sebagian gen 16-rRNA menunjukkan bahwa isolat 1Ub termasuk spesies Pseudoalteromonas piscicida, sedangkan SKT-b dan Ua termasuk spesies Vibrio alginolyticus. Kata kunci: bakteri probiotik, mekanisme penghambatan, V. harveyi, udang windu