Objective Lactobacillus antagonistic to Riemerella anatipestifer (RA) was isolated and evaluated in vitro and in vivo for application as a probiotic to prevent and control disease caused by the pathogen.

Method For the potential of being used as a probiotic, a strain of lactobacillus was isolated from fermented Brassica oleracea var. capitata. It was tested for tolerance to acid, bile salt, and simulated gastrointestinal fluid as well as growth under adverse conditions. With positive results, it was identified morphologically with 16S rRNA gene sequencing and whole-genome sequencing. Anti-RA activity and minimum inhibitory concentration of cell-free supernatant of its cultured broth were determined using the agar well diffusion method and a sublethal animal challenge test to evaluate its protective efficacy on RA-infected Muscovy ducklings.

Result Lactiplantibacillus plantarum SC-5 was isolated to be the candidate strain. Its metabolic pathways were complete, carbohydrate utilization broad, and detected antibiotic resistance and virulence genes being of intrinsically adaptable type with high biosafety and no pathogenic risk. It grew and proliferated well on culture showing the in vitro tolerance to pH 2.0 with a survival rate of 33.64% and to 0.5% bile salts of 18.64% in 12 h, robust viability in a simulated gastrointestinal environment, and being not susceptible to most macrolides, tetracyclines or aminoglycosides, susceptible to ampicillin, and only moderately susceptible to penicillin G or doxycycline. On an agar well inoculated with RA, the cell-free supernatant of SC-5 could produce a distinct inhibition zone reaching 16.07 mm and require a minimum supernatant dilution of 4×. In vivo, oral administration of SC-5 on ducklings significantly reduced the bacterial load in the peripheral blood of challenged birds (P＜0.05).

Conclusion L. plantarum SC-5 displayed outstanding probiotic properties with high biosafety and tolerance to adverse enternal conditions. Its significant in vitro and in vivo antibacterial activity against RA strongly suggested the applicability for disease prevention and control at waterfowl farming facilities.