The Thai Journal of Veterinary Medicine


Probiotic supplementation is now being focused as an alternative method to control fish diseases worldwide. This study investigates the in vitro efficacy of a human-derived probiotic, Lactobacillus rhamnosus. The first results of the screening for antimicrobial activity using agar spot test and disc diffusion showed that L. rhamnosus has a broad range against twelve isolates (n=12) of Gram-positive and Gram-negative pathogenic bacteria in fish and frogs : Streptococcus iniae (n=4), Streptococcus agalactiae (n=3), Aeromonas hydrophila (n=3), Chryseobacterium indologenes (n=1) and Edwardsiella tarda (n=1). Agar spot test on killed probiotic bacteria indicated that only the metabolic product of probiotic is involved in the growth inhibition of pathogenic bacteria. When confirmed by a co-culture study, the growth of all pathogenic bacteria that were cultured with a probiotic was lower than the control. All the findings suggest that L. rhamnosus has a high potential for inhibiting the growth of pathogenic bacteria in fish and frogs.

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