Chemical Characterization, Cell-Based Safety, and Antioxidant Assessments of Lactobacillus helveticus Postbiotics and Their Potential Antibacterial Effects and Mode of Action Against Food-Borne Multidrug-Resistant Staphylococcus aureus and Enterohaemorrhagic Escherichia coli O157:H7

This study aimed to determine the chemical profile, cell-based safety, antioxidant properties, antibacterial effect, and mode of action of Lactobacillus helveticus postbiotics (LHPs) against Escherichia coli O157:H7 and multidrug-resistant Staphylococcus aureus. LHPs exhibited significant radical scavenging activity (83.59% ± 4.21% for Hydroxyl RSA; 98.33% ± 2.47% for DPPH; and 21.67% ± 2.79% for linoleic acid peroxidation inhibitory), and antibacterial action toward MDR S. aureus (inhibition zone (IZ): 32.76 mm; minimum inhibitory concentration (MIC): 36.00 μg/mL; minimum bactericidal concentration (MBC): 45.00 μg/mL; minimal effective concentration (MEC): 25 mg/mL for whole milk, and 30 mg/mL for ground meat) and E. coli O157:H7 (IZ: 25.63 mm; MIC: 60.00 μg/mL; MBC: 90.00 μg/mL: MEC: 35 mg/mL for whole milk, and 45 mg/mL for ground meat) (p < 0.05). As an antimicrobial mode of action, significant alterations in the bacterial surface charge, membrane integrity, biofilm generation, auto-aggregation ability, and swimming/sliding motility, along with the subsequent intracellular content leakage from MDR S. aureus and E. coli O157:H7, were detected after treatment with LHPs (p < 0.05). LHPs exerted a promoting influence on MV-4-11 macrophage cell viability, leading to a considerable increase in the functions of SOD and GSH-Px in these cells. As well, LHPs caused a reduction in the production of NO and a drop in ROS levels (p < 0.05). Therefore, LHPs are a promising approach against MDR S. aureus and E. coli O157:H7 proliferations and have the capacity to be used in the food sector to combat safety issues caused by pathogenic microbes.