Table 2.

Examples of plant phenolics or phenolic-rich plant extracts with different antimicrobial mechanisms of action.

Plant phenolic or plant extract	Microorganism	Mechanisms of action	References
Nutgall (Quercus infectoria) extracts and their main constituents (namely gallic and tannic acids)	S. aureus	– no lysis but significant loss of tolerance to low osmotic pressure and high salt concentration following treatment with ethanol extract, one ethyl acetate fraction, gallic acid and tannic acid	Chusri and Voravuthikunchai, 2011
Ferulic acid or gallic acid (1 g·L−1, 30 min)	L. monocytogenes E. coli P. aeruginosa	– intracellular K+ efflux: membrane permeabilization	Borges et al., 2013
Berry phenolics	Salmonella enterica serovar Typhimurium S. enterica serovar Infantis	– can reduce outer membrane permeability in a similar manner to EDTA by releasing lipopolysaccharide (LPS) and chelating divalent cations or by intercalating into the outer membrane and replacing stabilizing cations	Nohynek et al., 2006
Ethanolic and water extracts of roselle (Hibiscus sabdariffa), rosemary (Rosmarinus officinalis), clove (Syzygium aromaticum), and thyme (Thymus vulgaris)	S. aureus E. coli	– decrease in internal pH and membrane hyperpolarization following treatment with extracts suggesting bacterial membrane damage	Gonelimali et al., 2018
Satureja montana and Origanum majorana decoctions (1.56 g·L−1)	S. aureus	– reversible alteration of membrane permeability following the first hours of exposure to Satureja montana and Origanum majorana decoctions	Gomes et al., 2020
Kombucha polyphenolic fraction	Vibrio cholerae	– fraction containing mainly catechin and isorhamnetin, as well as catechin and isorhamnetin permeabilizing the inner membrane of Vibrio cholerae	Bhattacharya et al., 2018
Chinese wild blueberries fraction with anthocyanins	L. monocytogenes, S. aureus, S. Enteritidis	– leakage of nucleic acids and proteins: membrane disruption	Zhou et al., 2020
Pinosylvin	Three S. enterica strains	– destabilization of the outer membrane of Salmonella cells partially abolished by MgCl2 addition indicating thus that part of its activity is related to the chelation of outer membrane stabilizing divalent cations, such as Mg2+	Plumed-Ferrer et al., 2013
3-p-trans-coumaroyl-2-hydroxyquinic acid from Cedrus deodara	S. aureus	– interaction with membrane lipid and protein, damage of cytoplasmic membrane with a significant membrane hyperpolarization, a loss of membrane integrity and severe morphological changes	Wu et al., 2016
Backhousia citriodora extract	Saccharomyces cerevisiae	– damage of the yeast cell membrane through penetration causing swelling and lysis leading to cell death	Alderees et al., 2018
p-hydroxybenzoic, protocatechuic, gallic, chlorogenic, vanillic, p-coumaric, and ferulic acids	L. monocytogenes	– decrease in extracellular pH (main mechanism of action for chlorogenic and gallic acids) – penetration or accumulation in the bacterial membrane of undissociated form (caffeic acid, p-hydroxybenzoic acid, protocatechuic acid, and vanillic acids) – dissociated form that is significantly antimicrobial (p-coumaric acid and ferulic acids)	Pernin et al., 2019
Olive leaf extract	L. monocytogenes	– loss of flagella and reduction of motility of L. monocytogenes cells following their treatment by sub-inhibitory concentrations of olive leaf extract	Liu et al., 2017a
Scopoletin and daphnetin (coumarins)	Bacillus subtilis	– increase in length of bacteria in the presence of the coumarins probably due to the lack of septum formation, hypothesis substantiated by screening for their ability to inhibit the bacterial cell division protein Escherichia coli FtsZ: – scopoletin inhibited the GTPase (GTP: guanosine triphosphate) activity of FtsZ in a noncompetitive manner – molecular docking studies of interactions of coumarins with the modeled FtsZ protein indicate that they bind to T7 loop, which is different from the GTP-binding site (active site) These data support the hypothesis of the role of coumarins in halting the first step of bacterial cell division process	Duggirala et al., 2014
Quercetin	E. coli	– DNA gyrase inhibition either by interaction of quercetin with DNA or with ATP binding site of gyrase	Plaper et al., 2003
Chlorogenic acid	B. subtilis	– induction of the intracellular metabolic imbalance of the tricarboxylic acid cycle and glycolysis, leading to metabolic disorder and death	Wu et al., 2020
Cranberry concentrate	E. coli O157:H7	– marked downregulation of hdeA (cell envelope protein), slp (outer membrane lipoprotein) and cfa (cell wall phospholipid synthesis) genes	Wu et al., 2009
Hydroxytyrosol	Lactobacillus plantarum	– upregulation of antioxidant response involving genes from the reactive oxygen species resistome of Lb. plantarum, genes coding for H2S-producing enzymes and genes involved in the response to thiol-specific oxidative stress – upregulation of a set of genes involved in cell wall biogenesis	Reverón et al., 2020
Gallic acid, protocatechuic acid and vanillic acid	Salmonella enterica serovar Typhimurium	– membrane permeabilization by the three phenolic acids – morphological defects at the polar ends of bacteria treated with gallic or protocatechuic acids – treatment by vanillic acid resulting in observation of mid-division cells suggesting a perturbation of the cell division process that allows for septum formation but prevents finalization – downregulation of all genes found in the Salmonella Pathogenicity Island 1 (SPI-1), which code for an assembly of proteins that aid in the attachment and subsequent invasion of host cells by gallic acid and downregulation of key regulatory genes by protocatechuic acid	Alvarado-Martinez et al., 2020
3-hydroxyphenylacetic acid (3-HPAA)	Pseudomonas aeruginosa	– proteomic analysis after 3-HPAA exposure of P. aeruginosa revealed changes in profile of proteins related to DNA replication and repair, RNA modifications, ribosomes and proteins, cell envelope, oxidative stress, as well as nutrient availability. 3-HPAA was thus classified as a multitarget antimicrobial agent	Ozdemir and Soyer, 2020