Abstract:To investigate the antibacterial activity of protocatechualdehyde (PC), the minimum inhibitory concentrations (MICs) of PC against C. sakazakii strains and the effect of PC on C. sakazakii growth curves were determined. The effect of PC on the cell morphology of C. sakazakii was observed under field emission scanning electron microscope. In addition, the impacts of PC on cell membrane integrity, intracellular pH (pHin), intracellular adenosine triphosphate (ATP) concentration and membrane potential were measured using multiple fluorescent probes to elucidate its possible antibacterial mechanism. The results showed that the MICs of PC against C. sakazakii strains ranged from 0.625 to 1.25 mg/mL, and the addition of PC significantly reduced the specific growth rate and the maximum optical density of C. sakazakii. Electronic microscopy observations indicated that C. sakazakii cells exposed to PC had a wrinkled surface and lost the typical structure of Corynebacterium spp. In addition, PC treatments at concentrations of 2MIC and 4MIC reduced cell integrity by 49.0% and 50.7%, respectively, and caused a decrease in pHin of C. sakazakii from 6.87 to 5.67 and 4.47, respectively; the PC treatments reduced the intracellular ATP concentration from 1.824 μmol/L to less than 0.01 μmol/L. In addition, cells treated with PC showed depolarized cell membranes. In conclusion, PC had good antibiotic activity against C. sakazakii, and its possible mechanism of action was to affect the permeability of the cell membrane. PC has the potential to be used as a natural antibacterial agent in infant formula or other foods.
