Robust Goat-Derived Enterococcus Isolates with Broad-Spectrum Antipathogenic Activity as Next-Generation Probiotic Candidates

The rise of multidrug-resistant enteric pathogens and increased demand for antibiotic alternatives have intensified efforts to find reliable, safe, and effective probiotics. This study reports the isolation, characterization, and assessment of the probiotic potential of five <i>Enterococcus</i> strains isolated from the feces of healthy goats aged 7-9 months raised under conventional management. Following an initial screening of 57 lactic acid bacteria, 5 isolates (<i>Enterococcus faecium</i>, <i>E. hirae</i>, <i>E. faecalis</i>, <i>Enterococcus</i> sp., and <i>Streptococcus lutetiensis</i>) were chosen based on their catalase-negative, non-motile, and non-hemolytic characteristics, in addition to their high tolerance to gastric (pH 2.0) and intestinal (pH 8.0, 0.3-1.5% bile salt) stress. In simulated gastric juice, survival rates reached 89.05% (E5) and 85.03% (E3), while in intestinal juice, survival peaked at 78.01% (E4). All strains thrived in 4% NaCl and maintained at least 8 Log₁₀ CFU/mL after 12 h of exposure to 1.5% porcine bile salt. Cell surface hydrophobicity (0.78-93.85%) and auto-aggregation (23-91%) properties were strain-dependent, but exceeded the thresholds required for efficient gut colonization. Co-aggregation assays demonstrated over 45% binding with <i>E. coli</i> and <i>S. typhimurium</i>, suggesting a strong potential to displace pathogens. Cell-free supernatants created inhibition zones measuring 15.02 mm against <i>E. coli</i> and 11.04 mm against <i>S. flexneri</i>, while maintaining activity against methicillin-resistant <i>S. aureus</i> (MRSA). Antibiotic testing indicated that all strains were sensitive to ciprofloxacin and florfenicol. No β-hemolysis or mobile resistance genes were found, supporting the initial safety findings. This study reveals that <i>Enterococcus</i> isolates from goats display a unique combination of gastrointestinal survivability and broad-spectrum antipathogenic activity and, therefore, are promising candidates for the development of next-generation probiotic strains for use in livestock (and, potentially, humans). Further in vivo validation and genome-based safety assessments are warranted.