Antimicrobial Properties of Probiotics As Animal Growth Promoters

Antibiotic growth promoters (AGPs) suppress the growth of infectious pathogens. These pathogens negatively impact agricultural production worldwide and often cause health problems if left untreated. Here, we evaluate six strains (BPR-11, BPR-12, BPR-13, BPR-14, BPR-16 and BPR-17), which are known for their ability to survive harsh environmental conditions, as AGP replacements in animal feed. Four of these strains (BPR-11, BPR-14, BPR-16 and BPR-17) showed antimicrobial activity against the pathogenic strains and at 25 μg/mL, with BPR-16 and BPR-17 also able to inhibit and at 100 μg/mL. Further chemical investigation of BPR-17 led to the identification of eight metabolites, namely C16, C15, C14 and C13 surfactin C (1-4), maculosin (5), maculosine 2 (6), genistein (7) and daidzein (8). Purified compounds (1-4) were able to inhibit all the tested pathogens with MIC values ranging from 6.25 to 50 μg/mL. Maculosin (5) and maculosine 2 (6) inhibited , and with an MIC of 25 μg/mL while genistein (7) and daidzein (8) showed no activity. An animal trial involving feeding BPR-11, BPR-16 and BPR-17 to a laboratory poultry model led to an increase in animal growth, and a decrease in feed conversion ratio and mortality. The presence of surfactin C analogues (3-4) in the gut following feeding with probiotics was confirmed using an LC-MS analysis. The investigation of these probiotics, their metabolites, their impacts on animal performance indicators and their presence in the gastrointestinal system illustrates that these probiotics are effective alternatives to AGPs.