Application of essential oils and d-amino acids for controlling methicillin-resistant Staphylococcus aureus isolated from dairy products

Staphylococcus (S.) aureus and its increasing antimicrobial resistance pose a significant challenge to global health. The rapid emergence of antibiotic resistance and the risks associated with chemical preservatives are major global concerns. Consequently, there is an important issue of developing effective control strategies in the food industry. This study aimed to determine the prevalence of S. aureus isolated from dairy products in Egypt. Additionally, antimicrobial resistance profiling was assessed. Finally, the potential use and sensory attributes of essential oils, such as olive and black seed oils, along with d-amino acids as antimicrobial additives in Domiati cheese under osmotic stress, were evaluated for controlling methicillin-resistant S. aureus. A total of 150 dairy samples were examined, including 30 samples each of raw milk, ultra-heat-treated (UHT) milk, Karish cheese, Domiati cheese and frozen dairy dessert. The results revealed that 32% of the examined samples were positive for S. aureus, with more than 70% of the isolates exhibiting multidrug resistance to tetracycline, erythromycin and oxacillin. Molecular characterisation showed that 23 and 7 isolates harboured the enterotoxin genes sea and seb, respectively. Furthermore, 72 and 4 isolates carried the nuc and mecA genes, respectively. Among the 10 examined d-amino acids, d-tryptophan (40 mM) demonstrated the most potent antibacterial activity. Our study also revealed, for the first time, the significant inhibitory effect of d-tryptophan on methicillin-resistant S. aureus (MRSA) in contaminated cheese. The number of MRSA cells treated with olive and black seed oils (1%) and d-tryptophan (40 mM) was significantly reduced by 2 to 5 log cfu/g in cheese (P < 0.05). The used natural additives improved overall acceptability and other sensory attributes of the cheese. The combination of essential oils and d-tryptophan presents a promising eco-friendly solution for controlling S. aureus contamination in the food industry.