6.2 Disruption of membranes

The outer bacterial membranes safeguard the bacterial cells from harsh environment, causing them to survive in extreme conditions. The inner membrane or the so-called cytoplasmic membrane regulates the uptake of solutes and minerals into the cell as well as the transport of proteins and other macromolecules. The alteration in membranes causes many adverse effects on functions of bacterial cells that might be very important for bacterial integrity, like uptake of mineral ions and nutrients. To study the membrane effects of antioxidants, fluorescence polarization methods using model membranes (consisting of two component: DPPC and POPC) are used. Fluorescence polarization increasingly alters in correspondence with reduction in membrane fluidity. MIC values are given in Table 3.

The antioxidants like polyhydroxyl flavans and catechin of green tea hinder the development of certain bacteria and affect Gram-positive and Gram-negative bacteria by damaging the structure of membranes of the bacterial cells (see Table 1).

#### 6.2.1 Sophoraflavanone G

Sophoraflavanone G, a phytochemical with intensive antibacterial activity, shows very low MICs (1.56—12.5 μg/ml) against Gram-positive bacteria than Gramnegative bacteria by altering membrane functions. Increased polarization in DPPC and POPC liposomes implies that sophoraflavanone G decreases membrane fluidity (for MIC value see Table 4) [15].

#### 6.2.2 Catechins

The pathogenicity of Gram-negative bacteria is linked to the lipopolysaccharide layer (reduce the sensitivity against antibacterial agents). That is why, the antibacterial agents demonstrate more activity for Gram-positive bacteria. Catechins intermingle and target bacterial membrane protein, fatty acid synthase, beta lactamase, and such other bacterial enzymes. Antibacterial catechins were reported to alter membrane fluidity [16]. Tea catechins impart specific agitation in the well-organized phosphatidylcholine and phosphatidylethanolamine bilayers that makeup membranes of bacteria. Epigallocatechin gallate (EGCG), a polyphenol obtained from green tea, black tea, and cocoa shows intensive activity, perturbs membranes of bacteria, and causes leakage of membranes isolated from E. coli. The antibacterial effects result from the interaction of catechins which interacts with oxygen, genes, and cell membranes, and these interactions produce their antibacterial effects. MIC values are given in Table 3.

EGCG binds straight to the peptidoglycan of S. aureus, affects integrity of cell and thereby decreases the acceptance of the cell to high osmotic pressure and less ionic strength. EGCG induces changes in morphology of Gram-negative bacteria depending on the acquittance of H2O2 and causes oxidative stress in bacteria. Flavonoids (epigallocatechin, myricetin, quercetin; structure shown below), damage membrane protein, and coagulate cytoplasm alter constituents of fatty acids and phospholipids, weaken mechanism of energy formation and metabolism, impacts the production of RNA and DNA, and abolishes translocation of proteins [17].

At 100 μg/ml ferulic acid and gallic acid cause 60% damage to the cytoplasmic membranes of P. aeruginosa. The uptake of propidium iodine (nucleic acid strain to which cell is impermeable) shows that FA and GA alter membrane integrity. In the outer membrane of Gram-positive and Gram-negative bacteria, porins (hydrophilic channels) are present that stops the hydrophobic substances from entering the cell. But some natural agents disintegrate the lipopolysaccharide layer and so damaging the permeability of the membrane causing nutrients to leak and effecting bacterial growth [20].

Moreover, bacterial cells have negative surface charge because of the ionic groups. The exposure to phenolic acids decreases this charge and the transport of solutes. Excess of phenolic acids cause hyper acidification that makes the cytoplasm acidic and denature the proteins present in the cytoplasm. So, the damage to mem-

Another factor that indicates the membrane damage is K<sup>+</sup> leakage. Because the

In bacterial cell the energy is required for the transport of solutes, uptake of metabolites, and biosynthesis of macromolecules. This energy comes from the respiratory chains like electron transport chain. Some antioxidants inhibit the respiratory chains at any step and thus depriving the cell of the energy necessary for

Reterochalcones stops the oxygen consumption in the targeted cells and inhibits the NADH oxidation in the membranes of bacteria. The electron transport chain is inhibited in between the CoQ and cytochrome c sites as shown in Figure 2. The inhibition of respiratory chains stops the supply of energy to the cells thus retarding

, any damage to the cytoplasmic membranes

brane by acidification potentially explains the activity of phenolic acid.

causes its leakage that indicates the damage as shown in Figure 2.

cell's internal environment is rich in K<sup>+</sup>

MIC values of antioxidants against bacterial strains.

Antioxidants: Natural Antibiotics

DOI: http://dx.doi.org/10.5772/intechopen.84864

6.3 Inhibition of energy metabolism

growth (see Table 1).

Table 5.

6.3.1 Reterochalcones

their growth [8, 21].

363

Epicatechin gallate (ECG) dramatically alters the physical properties of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) bilayers. They cause leakage from the membranes that is known to be pronounce by the presence of PE. So, at membrane level the antibacterial properties of catechins are due to their damage to PE. So, to estimate the phospholipid specificity, in the presence and absence of PE, egg yolk model was used. The results showed that only galloylated catechins affected PE and caused prominent leakage at 6.3 mol%. Protein translocation and other such processes are to some extent related to phospholipids; so, any effect on these can significantly alter the cell metabolism of bacteria [18]. Liposome membranes are damaged by EGCG and the leakage of intraliposomal CF occurs. This damage to membranes increases the permeability of catechins for catechins to penetrate in the cell. But how catechins damage the bilayer and penetrate the cell is still unanswered [19].

#### 6.2.3 Ferulic and gallic acid

FA and GA cause severe and irreversible damage to the membranes causing constant leakage of the essential cell constituents. Different physiological terms are used to access the antimicrobial activities: MIC, MBC, and K+ release in the cell. The MIC values of ferulic and gallic acids against some bacterial strains are listed in Table 5.


#### Table 5.

the well-organized phosphatidylcholine and phosphatidylethanolamine bilayers that makeup membranes of bacteria. Epigallocatechin gallate (EGCG), a polyphenol obtained from green tea, black tea, and cocoa shows intensive activity, perturbs membranes of bacteria, and causes leakage of membranes isolated from E. coli. The antibacterial effects result from the interaction of catechins which interacts with

EGCG binds straight to the peptidoglycan of S. aureus, affects integrity of cell and thereby decreases the acceptance of the cell to high osmotic pressure and less ionic strength. EGCG induces changes in morphology of Gram-negative bacteria depending on the acquittance of H2O2 and causes oxidative stress in bacteria. Flavonoids (epigallocatechin, myricetin, quercetin; structure shown below), damage membrane protein, and coagulate cytoplasm alter constituents of fatty

metabolism, impacts the production of RNA and DNA, and abolishes translocation

Epicatechin gallate (ECG) dramatically alters the physical properties of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) bilayers. They cause leakage from the membranes that is known to be pronounce by the presence of PE. So, at membrane level the antibacterial properties of catechins are due to their damage to PE. So, to estimate the phospholipid specificity, in the presence and absence of PE, egg yolk model was used. The results showed that only galloylated catechins affected PE and caused prominent leakage at 6.3 mol%. Protein translocation and other such processes are to some extent related to phospholipids; so, any effect on these can significantly alter the cell metabolism of bacteria [18]. Liposome membranes are damaged by EGCG and the leakage of intraliposomal CF occurs. This damage to membranes increases the permeability of catechins for catechins to penetrate in the cell. But how catechins damage the bilayer and penetrate the cell is

FA and GA cause severe and irreversible damage to the membranes causing constant leakage of the essential cell constituents. Different physiological terms are used to access the antimicrobial activities: MIC, MBC, and K+ release in the cell. The MIC values of ferulic and gallic acids against some bacterial strains are listed in Table 5.

oxygen, genes, and cell membranes, and these interactions produce their

acids and phospholipids, weaken mechanism of energy formation and

antibacterial effects. MIC values are given in Table 3.

of proteins [17].

Antioxidants

still unanswered [19].

6.2.3 Ferulic and gallic acid

362

MIC values of antioxidants against bacterial strains.

At 100 μg/ml ferulic acid and gallic acid cause 60% damage to the cytoplasmic membranes of P. aeruginosa. The uptake of propidium iodine (nucleic acid strain to which cell is impermeable) shows that FA and GA alter membrane integrity. In the outer membrane of Gram-positive and Gram-negative bacteria, porins (hydrophilic channels) are present that stops the hydrophobic substances from entering the cell. But some natural agents disintegrate the lipopolysaccharide layer and so damaging the permeability of the membrane causing nutrients to leak and effecting bacterial growth [20].

Moreover, bacterial cells have negative surface charge because of the ionic groups. The exposure to phenolic acids decreases this charge and the transport of solutes. Excess of phenolic acids cause hyper acidification that makes the cytoplasm acidic and denature the proteins present in the cytoplasm. So, the damage to membrane by acidification potentially explains the activity of phenolic acid.

Another factor that indicates the membrane damage is K<sup>+</sup> leakage. Because the cell's internal environment is rich in K<sup>+</sup> , any damage to the cytoplasmic membranes causes its leakage that indicates the damage as shown in Figure 2.

#### 6.3 Inhibition of energy metabolism

In bacterial cell the energy is required for the transport of solutes, uptake of metabolites, and biosynthesis of macromolecules. This energy comes from the respiratory chains like electron transport chain. Some antioxidants inhibit the respiratory chains at any step and thus depriving the cell of the energy necessary for growth (see Table 1).

#### 6.3.1 Reterochalcones

Reterochalcones stops the oxygen consumption in the targeted cells and inhibits the NADH oxidation in the membranes of bacteria. The electron transport chain is inhibited in between the CoQ and cytochrome c sites as shown in Figure 2. The inhibition of respiratory chains stops the supply of energy to the cells thus retarding their growth [8, 21].
