If food is contaminated with pathogens such asListeria monocytogenes, improper cooking during sous-vide preparation can lead to foodborne illnesses. In this study, it was found thatL. monocytogeneswere inactivated with both heat and the essential oil ofSalvia officinalis(sage EO) in beef tenderloin of themusculus psoas majorthat had undergone sous-vide processing. To determine whether the enhancement of the efficacy of heat treatment is prospective,L. monocytogenesand sage EO were mixed. Groups withL. monocytogenesalone and sage essential oil combined withL. monocytogenesand test groups without EO were established. The samples were vacuum-packed, inoculated withL. monocytogenes, and then cooked sous-vide for the predetermined duration at 50, 55, 60, or 65 °C. In both groups with sous-vide beef tenderloin, the total bacterial count, the coliforms bacterial count, and the amount ofL. monocytogeneswere assessed on days 0, 3, 6, 9, and 12. Over these days, the amounts ofL. monocytogenes, coliform bacteria, and overall bacteria increased. The identification of bacterial strains in various days and categories was performed by MALDI-TOF mass spectrometry. The test group that was exposed to a temperature of 50 °C for 5 min had a higher overall bacterial count for each day that was assessed.Pseudomonas fragiandL. monocytogeneswere the most isolated organisms from the test group and the treated group. To ensure the safety for the consumption of sous-vide beef tenderloin, it was found that the addition of natural antimicrobials could produce effective outcomes.