Characterization of Mammaliicoccus vitulinus Strains from Slovak Raw Goat Milk and Their In Vitro Susceptibility to Nisin and Postbiotic Substances

The genus Mammaliicoccus was recently reassigned from the family Staphylococcaceae. Mammaliicoccus spp. were first detected on German dairy farms, and exhibited a wide range of antimicrobial resistance genes. They are non-aureus agents frequently found in milk. Postbiotic substances (PSs) have recently emerged as a new class of functional biotics. Therefore, the objective of this study was to evaluate the in vitro effects of nisin and PS produced by autochthonous lactococci against Mammaliicoccus spp. (isolated from raw goat milk) to broaden their antimicrobial spectrum of inhibition and to indicate their potential use. Non-hemolytic, low-grade biofilm-forming (0.119 ± 0.034; 0.222 ± 0.047) strains of Mammaliicoccus vitulinus, Mv 33/3 and Mv 44, identified by sequencing, did not contain resistance genes for 15 antibiotics tested, and were susceptible to methicillin. They did not produce damaging enzymes or produced only a small amount (5–10 nmoL). In addition, they were susceptible to the bacteriocin nisin (inhibitory activities of 25,600 AU/mL and 51,200 AU/mL) and to PS produced by autochthonous lactococci (inhibitory activity of 400–800 AU/mL). Treatment of strains with postbiotic substances can minimize the risk of antibiotic resistance gene occurrence, thereby making products more stable during processing or storage.