Probiotic characterization of lactic acid bacteria isolated from maize silage stover for poultry feed applications

Abstract

Background: Antimicrobial resistance is a major concern in livestock production, and there is an urgent need for sustainable antibiotic alternatives. Maize silage stover is a source of a wide variety of microbial communities, but the probiotic properties of the native lactic acid bacteria (LAB) have not been extensively studied for use in poultry feeds. Aim: This study aimed to isolate and characterize autochthonous LAB strains from maize silage stover in Vietnam and assess their antimicrobial activity, gastrointestinal stress resistance, and molecular safety profile against avian pathogens. Methods: A total of 51 acid-producing colonies were isolated and subjected to a five-step selection procedure. The agar well diffusion method was used to test the antagonistic activity against Escherichia coli, Salmonella enterica, and Staphylococcus aureus in 30 confirmed LAB strains. Tolerance to osmotic pressure, gastric acid (pH 2.0, 3.0, and 4.0), and bile salts (0.2%–0.8%) was evaluated. The most promising isolate (M49) was further characterized using 16S rRNA gene sequencing and polymerase chain reaction was used to screen for virulence factors, antibiotic resistance genes, and biogenic amine production. Results: Isolate M49 demonstrated optimal broad-spectrum antagonism, with mean inhibition zones of 25.47, 17.53, and 15.67 mm against S. aureus, 17.53 mm against S. enterica, and 15.67 mm against E. coli. It exhibited high physiological resilience, maintaining weak but persistent viability at 0.8% bile salts and surviving moderate acid stress at pH 3.0. Phenotypic screening revealed that the isolate was γ-hemolytic and sensitive to key antibiotics. Preliminary PCR screening indicated the absence of targeted virulence and vancomycin resistance genes. The isolate was molecularly identified as Companilactobacillus sp. M49 (sharing 99.87% sequence identity with C. pabuli). Conclusion: Companilactobacillus sp. M49 is physiologically resilient and possesses strong antimicrobial activity, demonstrating its potential as a direct-fed microbial candidate for poultry production. Whole-genome sequencing and in vivo trials are required to validate the clinical efficacy and systemic safety of this drug.