Antibacterial Activity and Action Mode of Lactobionic Acid Against Cronobacter sakazakii: With Insights into Cell Wall, Membrane, and Macromolecule Targeting

Lactobionic acid (LBA) has demonstrated antibacterial activities against multiple foodborne bacteria; however, few studies have reported on its effect against <i>Cronobacter sakazakii</i>. In this study, the antibacterial activity and mode of LBA against <i>C. sakazakii</i> were explored. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of LBA against <i>C. sakazakii</i> were 12.5 and 25 mg/mL, respectively. LBA exhibited bacteriostatic activity at sub-MIC and bactericidal activity at concentrations ≥ MIC. Alkaline phosphatase (AKP) activity, cell outer membrane (OM) permeability, protein leakage, and gel electrophoresis results suggested that LBA increased the permeability of the cell wall and OM, leading to intracellular protein leakage and a decrease in protein contents and activity, indicating LBA damage to the cell wall and membrane. Among these, the rapid AKP activity surge reached 4.37 U/gprot at 2 MIC, and the OM permeability dramatically increased up to 10 min and stabilized after 30 min. Microscopic observations confirm the disruption to the cell wall and membrane, further showing that LBA disrupted the integrity of the cell wall and membrane. Moreover, LBA disturbs normal cellular functions by binding to deoxyribonucleic acid (DNA), as reflected by the competitive binding assay. Overall, LBA possesses potential multiple applications in the food industry due to its natural and antibacterial properties.