Bactericidal activity of catechin-copper (II) complexes on Escherichia coli ATCC11775 in the absence of hydrogen peroxide

Enhancing the antimicrobial activity of natural extraction using the synthetic ultrasmall metal nanoparticles

The use of Catechin as an antibacterial agent is becoming ever-more common, whereas unstable and easy oxidation, have limited its application. A simple and low-energy-consuming approach to synthesize highly stable and dispersive Catechin-Cu nanoparticles(NPs) has been developed, in which the stability and dispersivity of the NPs are varied greatly with the pH value and temperature of the reaction. The results demonstrate that the optimal reaction conditions are pH 11 at room temperature. As-synthesized NPs display excellent antimicrobial activity, the survival rates of bacterial cells exposed to the NPs were evaluated using live/dead Bacterial Viability Kit. The results showed that NPs at the concentration of 10 ppm and 20 ppm provided rapid and effective killing of up to 90% and 85% of S. aureus and E. coli within 3 h, respectively. After treatment with 20 ppm and 40 ppm NPs, the bacteria are killed completely. Furthermore, on the basis of assessing the antibacterial effects by SEM, TEM, and AFM, it was found the cell membrane damage of the bacteria caused by direct contact of the bacteria with the NPs was the effective mechanism in the bacterial inactivation.

Requirement of a plasmid-encoded catalase for survival of Rhizobium etli CFN42 in a polyphenol-rich environment

Nitrogen-fixing bacteria collectively called rhizobia are adapted to live in polyphenol-rich environments. The mechanisms that allow these bacteria to overcome toxic concentrations of plant polyphenols have not been clearly elucidated. We used a crude extract of polyphenols released from the seed coat of the black bean to simulate a polyphenol-rich environment and analyze the response of the bean-nodulating strain Rhizobium etli CFN42. Our results showed that the viability of the wild type as well as that of derivative strains cured of plasmids p42a, p42b, p42c, and p42d or lacking 200 kb of plasmid p42e was not affected in this environment. In contrast, survival of the mutant lacking plasmid p42f was severely diminished. Complementation analysis revealed that the katG gene located on this plasmid, encoding the only catalase present in this bacterium, restored full resistance to testa polyphenols. Our results indicate that oxidation of polyphenols due to interaction with bacterial cells results in the production of a high quantity of H(2)O(2), whose removal by the katG-encoded catalase plays a key role for cell survival in a polyphenol-rich environment.

Effect of tannins on the in vitro growth of Escherichia coli O157:H7 and in vivo growth of generic Escherichia coli excreted from steers

The effect of commercially available chestnut and mimosa tannins in vitro (experiment 1) or in vivo (experiment 2) on the growth or recovery of Escherichia coli O157:H7 or generic fecal E. coli was evaluated. In experiment 1, the mean growth rate of E. coli O157:H7, determined via the measurement of optical density at 600 nm during anaerobic culture in tryptic soy broth at 37 degrees C, was reduced (P < 0.05) with as little as 400 microg of either tannin extract per ml of culture fluid. The addition of 200, 400, 600, 800, and 1,200 microg of tannins per ml significantly (P < 0.01) reduced the specific bacterial growth rate when compared with the nontannin control. The specific growth rate decreased with increasing dose levels up to 800 microg of tannins per ml. Bacterial growth inhibition effects in chestnut tannins were less pronounced than in mimosa tannins. Chestnut tannin extract addition ranged from 0 to 1,200 microg/ml, and a linear effect (P < 0.05) was observed in cultures incubated for 6 h against the recovery of viable cells, determined via the plating of each strain onto MacConkey agar, of E. coli O157:H7 strains 933 and 86-24, but not against strain 6058. Similar tests with mimosa tannin extract showed a linear effect (P < 0.05) against the recovery of E. coli O157:H7 strain 933 only. The bactericidal effect observed in cultures incubated for 24 h with the tannin preparations was similar, although it was less than that observed from cultures incubated for 6 h. When chestnut tannins (15 g of tannins per day) were infused intraruminally to steers fed a Bermuda grass hay diet in experiment 2, fecal E. coli shedding was lower on days 3 (P < 0.03), 12 (P = 0.08), and 15 (P < 0.001) when compared with animals that were fed a similar diet without tannin supplementation. It was concluded that dietary levels and sources of tannins potentially reduce the shedding of E. coli from the gastrointestinal tract.

Involvement of cytoplasmic membrane damage in the copper (II)-dependent cytotoxicity of a novel naturally occurring tripyrrole

In the presence of a nonlethal concentration of Cu(II), washed Escherichia coli ATCC8739 cells were killed by a novel tripyrrole 1, isolated as a red pigment from the Serratia sp. Cell killing was accompanied by a depletion in the potassium pools of the cells due to the damage to the cytoplasmic membrane, without any detectable DNA damage as revealed by the transformed plasmid DNA and phage induction assay. This revealed that the bactericidal activity of compound 1 in the presence of Cu(II) results from membrane damage. Induction of endogenous catalase in the E. coli cells increased their resistance against the combination of compound 1 and Cu(II). Although compound 1 alone generated large amount of reactive oxygen species (ROS), it did not show any cell killing against E. coli in the absence of Cu(II). The Cu(II)-dependent bactericidal activity of compound 1 was suppressed by ethylenediaminetetraacetate, bathocuproine, catalase and superoxide disumutase (SOD), but not by dimethyl sulfoxide. These findings suggest that recycling redox reactions between Cu(II) and Cu(I), involving compound 1 and hydrogen peroxide on the cell surface, must be important in the mechanism of the killing. Compound 1 alone showed selective bactericidal activity against the gram positive bacterium, Bacillus cereus ATCC 6630, possibly due to its differential cellular transport.

Cytotoxicity of epigallocatechin-3-gallate to LNCaP cells in the presence of Cu2+

Epigallocatechin-3-gallate (EGCG) has shown remarkably anti-cancer activity, with its bioactivity being related to reactive conditions, such as pH and metal ions. The present study investigated the degradation of EGCG and its effect on prostate cancer cell in the presence of Cu2+. EGCG was incubated with prostate cancer cells, LNCaP, pretreated with or without Cu2+. EGCG in F-12 medium was quantified using HPLC and the viability of cells was assessed by gel electrophoresis, flow cytometry, and electron microscope. The results of HPLC showed that EGCG degraded completely within 12 h in F-12 medium with or without Cu2+. Gel electrophoresis and flow cytometry did not detect apoptosis of LNCaP cells when they were incubated with EGCG. Electron microscopy examination revealed that EGCG-Cu2+ complex led to damage of cytoplasm membrane in LNCaP cells. It was speculated that not EGCG, but its oxide and complex with Cu2+, are the bioactive components responsible for its cytotoxicity to LNCaP prostate cancer cells.

Epicatechin-copper 9II) complexes: Damage of small intestinal epithelium

Four epicatechins [(−)-epicatechin (EC), (−)-epicatechin gallate (ECg), (−)-epigallocatechin (EGC), (−)-epigallocatechin gallate (EGCg)] and their corresponding copper complexes were compared with regard to their effect on the viability of Caco-2 colon cancer cells in vitro, measured by 3-(4,5-dimethylthyazol-2-yl) 2,5-diphenyltetrazolium bromide (MTT) assay. The viability of Caco-2 cells exposed to EC (1 mM), ECg (1 mM) or EGC (1mM) respectively, for 30 min, was comparable to that of the saline control group, while EGCg (1 mM) apparently enhanced cellular activity. in contrast, the cells treated with epicatechin-copper complexes were killed. Bivalent copper 91 mM), in similar conditions, did not affect the cells. No cell leakage or other histological differences were observed, implying a rapid cell death. The suggested mechanism of killing is by OH radical attack, produced in the presence of epicatechin-copper complexes, but not in the presence of either of the epicatechins or copper alone. The reaction sites are discussed.

Bactericidal activity of catechin-copper (II) complexes against Staphylococcus aureus compared with Escherichia coli

The bactericidal activity of catechin-copper (II) complexes against Staphylococcus aureus compared with Escherichia coli was investigated in relation to the generation of hydrogen peroxide and the binding of Cu(II) ion onto the bacteria. The bactericidal activity of catechin-Cu(II) complexes against Staph. aureus (Gram-positive) was much lower than that against E. coli (Gram-negative), suggesting that the binding of copper ions to the surface of bacterial cells plays an important role in the bactericidal activity of catechin-Cu(II) complexes.

Damage to the cytoplasmic membrane of Escherichia coli by catechin-copper (II) complexes

In the presence of a nonlethal concentration of Cu(II), washed Escherichia coli ATCC11775 cells were killed by (-)-epigallocatechin (EGC) and (-)-epicatechin (EC). Cell killing was accompanied by a depletion in both the ATP and potassium pools of the cells, but the DNA double strand was not broken, indicating that the bactericidal activity of catechins in the presence of Cu(II) results from damage to the cytoplasmic membrane. Induction of endogenous catalase in E. coli cells increased their resistance to being killed by the combination of catechins and Cu(II). In all cases studied, EGC and EC with Cu(II) were found to generate hydrogen peroxide, but its concentration was too low to account for the bactericidal activity. The bactericidal activity of EGC in the presence of Cu(II) was completely suppressed by ethylenediaminetetraacetate, bathocuproine, catalase, superoxide disumutase (SOD), heated catalase, and heated SOD, but not by dimethyl sulfoxide. When catalase, either heated or unheated, was added to the cells incubated with EGC in the presence of Cu(II), it completely inhibited further killing of the cells. These findings suggest that recycling redox reactions between Cu(II) and Cu(I), involving catechins and hydrogen peroxide on the cell surface, must be important in the mechanism of the killing.

DNA cleavage activities of (-)-epigallocatechin, (-)-epicatechin, (+)-catechin, and (-)-epigallocatechin gallate with various kinds of metal ions

The DNA cleavage activities of (+)-catechin (C), (-)-epicatechin (EC), (-)-epigallocatechin (EGC), and (-)-epigallocatechin gallate (EGCg) were examined with 16 different metal ions. Cu(2+) with all the catechins facilitated DNA cleavage, while Ag+ with EGC and EC showed a strong repressive effect. The other metal ions examined showed little effect.