In Vitro Efficacy of Human-Derived Probiotic, Lactobacillus rhamnosus Against Pathogenic Bacteria in Fish and Frogs

Abstract

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.