Antibacterial Spectrum of Plant Polyphenols and Extracts Depending upon Hydroxyphenyl Structure

The relationship between the structure and antibacterial activity of 22 polyphenols was analyzed by using minimum inhibitory concentration (MIC) as a criterion against 26 species of bacteria which can grow in Mueller?Hinton medium. There was no clear correlation between Gram-staining and bacterial susceptibility to polyphenols, and the extent of the susceptibility was approximately dependent on the species of bacteria. In the same Gram-negative bacteria, the antibacterial activity of the polyphenols against Aeromonas hydrophila, Vibrio parahaemolyticus and Vibrio vulnificus was comparatively strong. On the other hand, the activity against 11 species of the Enterobacteriaceae was comparatively weak, and the activity against six species of aerobic bacteria causing plant disease was moderate. Polyphenols having pyrogallol groups showed strong antibacterial activity, and those with catechol and resorcinol rings showed lower activity. The structure?activity relationship was extended to 26 polyphenol-rich plant extracts which could have potent antibacterial activity suitable for commercial use

Antimicrobial Activity of 10 Different Plant Polyphenols against Bacteria Causing Food-Borne Disease

The antibacterial activities of 10 different plant polyphenols were evaluated by comparing their minimum inhibitory concentrations (MICs) against several food-borne pathogenic bacteria, Staphylococcus aureus (20 strains), some serotypes of the genus Salmonella (26 strains), Escherichia coli (23 strains), and some species of the genus Vibrio (27 strains). The polyphenols examined were epigallocatechin (1), epigallocatechin-3-O-gallate (2), punicalagin (3), tannic acid (4), castalagin (5), prodelphinidin (6), geraniin (7), procyanidins (8), a theaflavin mixture of black tea (9), and green tea polyphenols treated with loquat polyphenol oxidase (10). The average MICs of all polyphenols against S. aureus and the genus Vibrio (192±91 and 162±165 μg/ml, respectively) were much lower than the values against the genus Salmonella and E. coli (795±590 and 1519±949 μg/ml, respectively) (p<0.01). The coefficient of variation of the MICs of all polyphenols against S. aureus was the least and that against the genus Vibrio was the greatest. The mean MICs of each plant polyphenol against S. aureus (98?389 μg/ml) and the genus Vibrio (68?488 μg/ml) were similar. The relatively lower mean MIC values of 1, 2, 5, and 6 suggest the importance of 3,4,5-trihydroxyphenyl groups in antibacterial activity

Mechanism of Synergy between Epigallocatechin Gallate and β-Lactams against Methicillin-Resistant Staphylococcus aureus

Compared to MICs (more than 800 μg/ml) of (−)-epigallocatechin gallate (EGCg) against Escherchia coli, MICs of EGCg against methicillin-susceptible and methicillin-resistant Staphylococcus aureus (MSSA and MRSA) were 100 μg/ml or less. Furthermore, less than 25 μg EGCg per ml obviously reversed the high level resistance of MRSA to all types of tested β-lactams, including benzylpenicillin, oxacillin, methicillin, ampicillin, and cephalexin. EGCg also induced a supersusceptibility to β-lactams in MSSA which does not express mecA, encoding penicillin-binding protein 2′ (PBP2′). The fractional inhibitory concentration (FIC) indices of the tested β-lactams against 25 isolates of MRSA were from 0.126 to 0.625 in combination with 6.25, 12.5 or 25 μg of EGCg per ml. However, no synergism was observed between EGCg and ampicillin against E. coli. EGCg largely reduced the tolerance of MRSA and MSSA to high ionic strength and low osmotic pressure in their external atmosphere, indicating damage of the cell wall. Unlike dextran and lipopolysaccharide, peptidoglycan from S. aureus blocked both the antibacterial activity of EGCg and the synergism between EGCg and oxacillin, suggesting a direct binding of EGCg with peptidoglycan on the cell wall. EGCg showed a synergistic effect with dl-cycloserine (an inhibitor of cell wall synthesis unrelated to PBP2′) but additive or indifferent effect with inhibitors of protein and nuclear acid synthesis. EGCg did not suppress either PBP2′ mRNA expression or PBP2′ production, as confirmed by reverse transcription-PCR and a semiquantitative PBP2′ latex agglutination assay, indicating an irrelevance between the synergy and PBP2′ production. In summary, both EGCg and β-lactams directly or indirectly attack the same site, peptidoglycan on the cell wall. EGCg synergizes the activity of β-lactams against MRSA owing to interference with the integrity of the cell wall through direct binding to peptidoglycan

Growth parameter and viability modifications of escherichia coli by phenolic compounds and argentine wine extracts

The anti-bacterial effect of pure non-flavonoids gallic, vanillic, protocatechuic, and caffeic acids and flavonoids quercetin, rutin, and catechin and the effect of total polyphenols of three Argentinean wine varieties, Cabernet Sauvignon, Malbec, and Merlot, against Escherichia coli, microorganism frequently detected in fresh and processed foods, was investigated. The hydroxycinnamic derivate caffeic acid and the flavonoid quercetin were the more effective against E. coli. The polyphenol effect was ethanol independent. The E. coli decimal reduction times were 2.9, 2.1, and 0.65 h for Malbec wine and 2.8, 2.3, and 0.64 h for Merlot wine with respect to 1×, 2×, and 4× concentrated wine samples, respectively. For Cabernet Sauvignon wine, the values were 6.3, 3.7, and 1.28 h for 1×, 2×, and 4× concentrated samples, respectively. With clarified wines, the decimal reduction times were higher with values ranging from 15 to 18.4 h in the wine samples. So the phenolic compounds present in red wines could be considered as an interesting alternative to be used as natural preservative against pathogenic microorganisms.Fil: Rodriguez Vaquero, Maria Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Centro de Referencia para Lactobacilos; Argentina. Universidad Nacional de Tucumán. Facultad de Bioquímica, Química y Farmacia; ArgentinaFil: Manca, Maria Cristina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Centro de Referencia para Lactobacilos; Argentina. Universidad Nacional de Tucumán. Facultad de Bioquímica, Química y Farmacia; Argentin

Legionella pneumophila Replication in Macrophages Inhibited by Selective Immunomodulatory Effects on Cytokine Formation by Epigallocatechin Gallate, a Major Form of Tea Catechins

Epigallocatechin gallate (EGCg) is a major form of tea catechin and has a variety of biological activities, including antitumor as well as antimicrobial activity against some pathogens. Although the biological activities of EGCg have been extensively studied, its immunological effects are not well known. In the present study, the ability of EGCg to modulate macrophage immune functions in an in vitro Legionella pneumophila infection model of macrophages was examined. The study showed that EGCg inhibited the growth of L. pneumophila in macrophages at a concentration as low as 0.5 μg/ml without any direct antibacterial effect on the organisms. The EGCg selectively upregulated the production of interleukin-12 (IL-12) and tumor necrosis factor alpha (TNF-α) and downregulated IL-10 production of macrophages induced by L. pneumophila infection in a dose-dependent manner, but did not alter IL-6 production even at a high dose. The upregulation of the levels of macrophage gamma interferon (IFN-γ) mRNA by EGCg was also demonstrated. Treatment of macrophage cultures with anti-TNF-α and anti-IFN-γ monoclonal antibodies markedly abolished the anti-L. pneumophila activity of macrophages induced by the EGCg treatment. These results indicate that EGCg selectively alters the immune responses of macrophages to L. pneumophila and leads to an enhanced anti-L. pneumophila activity of macrophages mediated by enhanced production of both TNF-α and IFN-γ. However, the enhancement of in vitro anti-L. pneumophila activity by EGCg may not be directly mediated by IL-10 and IL-12 production modulation. Thus, the results of this study revealed the immunomodulatory effect of EGCg on macrophages, which have a critical role in infections