Screening of lactic acid bacteria inhibiting xanthine oxidase and safety evaluation

This study aimed to screen lactic acid bacteria (LAB) strains with potent xanthine oxidase (XOD)-inhibitory activity for potential application in reducing uric acid levels in poultry. A two-tiered approach was employed. First, we performed in vitro screening: The XOD inhibition rates of cell-free extracts (CFEs) from 26 LAB strains were determined. Four high-performing strains (A2, A6, SC, SN) were subsequently evaluated for the inhibition rates of their cell-free supernatants (CFSs). Further in vitro characterization included assessing their tolerance to artificial gastrointestinal fluids and antibiotic susceptibility profiling against 21 antimicrobials. The strains were identified via 16S rDNA sequencing. Subsequently, an in vivo safety study was conducted: mice received daily intraperitoneal injections of bacterial suspensions (10¹⁰ CFU/mL) for two weeks, with the incidence of mortality and organ lesions monitored. In vitro, the CFEs of strains A2, A6, SC, and SN exhibited XOD inhibition rates of 23.41%, 27.45%, 24.47%, and 27.23%, respectively, while their CFSs showed rates of 14.26%, 17.02%, 22.34%, and 19.57%. All four strains demonstrated high gastrointestinal tolerance, maintaining viable counts of above 10⁸ CFU/mL post-digestion. They were sensitive to key antibiotics like cephalosporins, macrolides, and penicillins. Molecular identification classified them as Lactobacillus paracasei (A2), Lactobacillus plantarum (A6), Lactobacillus brevis (SC), and Lactobacillus rhamnosus (SN). Critically, the in vivo safety assay revealed no mortality or organ lesions in mice treated with any of the four strains. Four LAB strains with potent in vitro XOD-inhibitory activity and proven in vivo safety were obtained, offering promising candidates for probiotic control of avian hyperuricemia.