Probiotic Properties In Vitro of Bacillus velezensis FJAT-57093 with Antibacterial Activity Against the Aquatic Pathogen Aeromonas hydrophila

TL;DR

This study identifies a probiotic strain, Bacillus velezensis FJAT-57093, with strong antibacterial activity against several aquatic pathogens and good probiotic properties for animal feed.

Contribution

The novel contribution is the identification and in vitro characterization of B. velezensis FJAT-57093 as a promising probiotic with broad-spectrum antibacterial activity against aquatic pathogens.

Findings

Bacillus velezensis FJAT-57093 showed strong antibacterial activity against Aeromonas hydrophila and other aquatic pathogens.

The strain exhibited high tolerance to simulated gastrointestinal conditions and produced extracellular enzymes and antioxidants.

Safety assessment confirmed the strain's non-hemolytic nature and susceptibility to ten antibiotics.

Abstract

The aim of this study was to acquire endospore-former(s) for aquatic animal feed based on the probiotic potential in vitro, including the anti-pathogen spectrum, gastrointestinal fluid tolerance, antioxidant activity, enzyme-producing ability, and basic safety assessment. The strain Bacillus velezensis FJAT-57093 was found to exhibit the strongest antibacterial ability against Aeromonas hydrophila in the agar well diffusion inhibition assays from 111 Bacillus-like strains. Moreover, the results showed that the compounds of the strain FJAT-57093 enriched by acid precipitation might be the main antibacterial metabolites. The strain FJAT-57093 also exhibited antibacterial effects against the aquatic pathogens Photobacterium damselae, Edwardsiella tarda, Vibrio parahaemolyticus, and Vibrio vulnificus. The safety assessment revealed that the strain FJAT-57093 was non-hemolytic and susceptible to ten antibiotics. The putative virulence and antibiotic resistance genes predicted were predominantly intrinsic to the FJAT-57093 genome. Furthermore, the strain FJAT-57093 demonstrated a tolerance of acid and bile salt under the simulated gastrointestinal tract conditions, extracellular enzyme-producing abilities, as well as an auto-aggregation rate of 45.88% at 24 h and co-aggregation rates with the aforementioned five aquatic pathogens, ranging from 14.87% to 58.55%. Additionally, its extracellular metabolites displayed strong antioxidant activities, with ABTS+ and DPPH radical scavenging rates of up to 99.82% and 42.74%, respectively. In summary, the strain B. velezensis FJAT-57093 was found to possess strong antibacterial activities against multiple aquatic pathogens and desirable in vitro probiotic properties.

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