Selection of probiotics by various inhibition test methods for use in the culture of western king prawns, Penaeus latisulcatus (Kishinouye)

The growth inhibition ability of nine probiotic strains were investigated against 15 Vibrio spp. isolated from western king prawns, Penaeus latisulcatus (Kishinouye), and eight pathogenic Vibrio strains from other aquatic animals. Five different inhibition test methods such as bacteriocin-like inhibitory substance (BLIS), modified BLIS, disc-diffusion, well-diffusion and co-culture method were compared in order to select the most suitable probiotics for use in the culture of western king prawns. The results showed that the modified BLIS method was the most effective one for the selection of probiotics. Pseudomonas synxantha and P. aeruginosa were promising probiotics as they caused a significantly higher (P < 0.05) growth inhibition of all the Vibrio spp. tested, with Pseudomonas aeruginosa being more effective than P. synxantha. The growth inhibition zones were significantly greater (P < 0.05) when probiotics were grown on Marine Salt Agar (MSA) for three days before inoculating the plate with the Vibrio spp., but were not significantly different (P > 0.05) when the probiotics and the Vibrio spp. were inoculated onto the plate at the same time. In the co-culture method, probiotics at a concentration of 103 CFU/mL allowed the Vibrio spp. (103 CFU/mL) to grow, but the Vibrio spp. cell densities never reached beyond their initial inoculum levels during the culture. At higher concentrations (105-107 CFU/mL), the probiotics dominated the growth of the Vibrio spp. Therefore, administering a suitable concentration of probiotics and allowing growth and production of antimicrobial compounds before the addition of Vibrio spp. produced the best inhibition results.