Susceptibility to Postbiotic Substances-Enterocins of the Strains Enterococcus thailandicus from Beavers (Castor fiber)

Eurasian beaver (<i>Castor fiber</i>) populations have been reintroduced to European countries, though this bears the risk of novel wildlife pathogen reservoir establishment. The species nova <i>E. thailandicus</i> was described first in Thailand as a food-derived strain. Later, this species was detected in the feces of pigs, poultry, sewage, and humans. In those studies, the potential risk posed by this species was evaluated. Against that background, the aim of this study was to investigate the susceptibility to postbiotic active substances (enterocins) against fecal <i>E. thailandicus</i> strains from beavers caught in Poland. The strains were identified with the use of 16S rRNA gene similarity sequencing. These six <i>E. thailandicus</i> strains with low-grade biofilm-forming abilities and two strains with the presence of the <i>gelE</i> virulence factor gene were susceptible to seven enterocins produced by non-autochthonous strains, mostly of the species <i>E. faecium</i> and <i>E. durans</i>. The inhibitory activity against the tested strains reached 25,600 AU/mL. Although the studied <i>E. thailandicus</i> strains did not show a strictly pathogenic character, their growth inhibition by postbiotics was identified as a novel elimination strategy.