In Vitro and In Vivo Evaluation of Lacticaseibacillus rhamnosus GG and Bifidobacterium lactis Bb12 Against Avian Pathogenic Escherichia coli and Identification of Novel Probiotic-Derived Bioactive Peptides.

Avian pathogenic E. coli (APEC), an extra-intestinal pathogenic E. coli (ExPEC), causes colibacillosis in poultry and is also a potential foodborne zoonotic pathogen. Currently, APEC infections in poultry are controlled by antibiotic medication; however, the emergence of multi-drug-resistant APEC strains and increased restrictions on the use of antibiotics in food-producing animals necessitate the development of new antibiotic alternative therapies. Here, we tested the anti-APEC activity of multiple commensal and probiotic bacteria in an agar-well diffusion assay and identified Lacticaseibacillus rhamnosus GG and Bifidobacterium lactis Bb12 producing strong zone of inhibition against APEC. In co-culture assay, L. rhamnosus GG and B. lactis Bb12 completely inhibited the APEC growth by 24 h. Further investigation revealed that antibacterial product(s) in the culture supernatants of L. rhamnosus GG and B. lactis Bb12 were responsible for the anti-APEC activity. The analysis of culture supernatants using LC-MS/MS identified multiple novel bioactive peptides (VQAAQAGDTKPIEV, AFDNTDTSLDSTFKSA, VTDTSGKAGTTKISNV, and AESSDTNLVNAKAA) in addition to the production of lactic acid. The oral administration (10 CFU/chicken) of L. rhamnosus GG significantly (P < 0.001) reduced the colonization (~ 1.6 logs) of APEC in the cecum of chickens. Cecal microbiota analysis revealed that L. rhamnosus GG moderated the APEC-induced alterations of the microbial community in the cecum of chickens. Further, L. rhamnosus GG decreased (P < 0.05) the abundance of phylum Proteobacteria, particularly those belonging to Enterobacteriaceae (Escherichia-Shigella) family. These studies indicate that L. rhamnosus GG is a promising probiotic to control APEC infections in chickens. Further studies are needed to optimize the delivery of L. rhamnosus GG in feed or water and in conditions simulating the field to facilitate its development for commercial applications.