Antimicrobial mechanism of 4-hydroxyphenylacetic acid on Listeria monocytogenes membrane and virulence

4-Hydroxyphenylacetic acid (4-HPCA) is the major intestinal metabolite of kaempferol and polymeric proanthocyanidins whereas the effect of 4-HPCA on Listeria monocytogenes remains unknown. In this study, we investigated the effect and mechanism of action of 4-HPCA on the highly lethal foodborne pathogen Listeria monocytogenes. Our results indicated that 4-HPCA inhibited L. monocytogenes growth and proliferation in a dose-dependent manner. In particular, L. monocytogenes displayed negligible growth or proliferation after 4-HPCA treatment (15.61 mM) for 24 h. The impact of 4-HPCA on cell membrane structure and function was investigated in terms of fluorometric cell membrane integrity, zeta potential and relative electrical conductivity. We observed an approximately 15 % fluorescence reduction in the cell membrane after MIC treatment. The zeta potential of the bacteria shifted significantly from-49.74 to-43.70 mV,-36.65 mV and-37.97 mV after treatment with 4-HPCA at the MIC for 0 h, 3 h and 12 h, respectively. The absolute value of the relative electrical conductivities increased significantly following 3 h, 6 h, 9 h and 15 h of 4-HPCA treatment at the MIC level. The results of scanning electron microscopy (SEM) showed that cells treated with 4-HPCA displayed a wrinkled morphology and irregular shapes. Moreover, 4-HPCA obviously decreased the expression of three virulence genes (hlyA, prfA, and inlA) in L. monocytogenes after 12 h of treatment. All these results verified that 4-HPCA, as an effective antibacterial compound against L. monocytogenes, could cause cell death through cell membrane damage and decrease the expression of three virulence factors. (c) 2021 Elsevier Inc. All rights reserved.

Automated summary

4-HPCA inhibits the growth and proliferation of L. monocytogenes in a dose-dependent manner by affecting cell membrane structure and function, as well as decreasing the expression of virulence genes, which may lead to cell death.