280
A polyphenolic compound, hamamelitannin, extracted from the bark of
Hamamelis virginiana significantly reduces biofilm activity of various microorganisms (Cobrado et al. 2012). Similarly, a monoterpenic phenol, carvacrol, had an
effect on the biofilms formed by Staphylococcus aureus and Salmonella enterica
serovar Typhimurium (Knowles et al. 2005). This compound, together with thymol,
is the principal phenolic component that contributes to the antimicrobial property of
oregano oil on staphylococci (Nostro et al. 2007). These molecules, possessing a
hydrophobic nature, interact with the lipid bilayer of cytoplasmic membrane causing alterations in its structural and functional properties and loss of integrity of
bacterial cell. Furthermore, these compounds may diffuse through the polysaccharide matrix of the biofilm resulting in its destabilization.
11.4 Synergistic Activity of Plant Compounds
Several plant compounds can be used along with known antibiotics to increase their
potency and to avoid undesirable side effects. Knowledge on the synergistic activity
of various phytochemicals could further boost the usage of medicinal plants, extracts
or natural products, either alone, combined with each other or along with antibiotics. The effect of ethyl gallate on β-lactam susceptibility in methicillin-resistant and
methicillin-sensitive strains of Staphylococcus aureus was studied by Shibata et al.
(2005) and found that it enhanced the activity of the antibiotic. This synergistic
effect of the alkyl gallates is specific for β-lactam antibiotics, and it does not cause
any change in the effectiveness of other classes of antibiotics tested.
Another remarkable study was conducted on the effect of 5- methoxyhydnocarpin,
a compound isolated from chaulmoogra oil, on the activity of berberine (Stermitz
et al. 2000), and the results indicated that 5-methoxyhydnocarpin enhanced the
action of berberine against Staphylococcus aureus even though it did not show any
antimicrobial activity on its own. It is observed that the accumulation level of berberine in the cells increased sharply in the presence of 5-methoxyhydnocarpin,
allowing this natural product to deactivate the mechanism of bacterial resistance
against berberine. In the absence of 5-methoxyhydnocarpin, berberine is easily
extruded by the multidrug resistance pumps of Staphylococcus aureus. This indicates the potential use of a weak antimicrobial natural compound along with another
compound to intensify its activity (Ríos and Recio 2005). Table 11.1 gives a combination of natural products and synthetic drugs used to combat fungal infections.
11.5 Antiviral Compounds
Plants have enormous biosynthetic capacity, and the complexity of their bioactive
constituents seems to provide a rich source of natural compounds that may serve as
excellent phytotherapeutic agents (Schmidt et al. 2008). The development of antimicrobial drugs that are plant derived has not progressed, especially, in the case of
antiviral chemotherapy as compared to antifungal and antibacterial due to the
R. Reghu et al.
A polyphenolic compound, hamamelitannin, extracted from the bark of
Hamamelis virginiana significantly reduces biofilm activity of various microorganisms (Cobrado et al. 2012). Similarly, a monoterpenic phenol, carvacrol, had an
effect on the biofilms formed by Staphylococcus aureus and Salmonella enterica
serovar Typhimurium (Knowles et al. 2005). This compound, together with thymol,
is the principal phenolic component that contributes to the antimicrobial property of
oregano oil on staphylococci (Nostro et al. 2007). These molecules, possessing a
hydrophobic nature, interact with the lipid bilayer of cytoplasmic membrane causing alterations in its structural and functional properties and loss of integrity of
bacterial cell. Furthermore, these compounds may diffuse through the polysaccharide matrix of the biofilm resulting in its destabilization.
11.4 Synergistic Activity of Plant Compounds
Several plant compounds can be used along with known antibiotics to increase their
potency and to avoid undesirable side effects. Knowledge on the synergistic activity
of various phytochemicals could further boost the usage of medicinal plants, extracts
or natural products, either alone, combined with each other or along with antibiotics. The effect of ethyl gallate on β-lactam susceptibility in methicillin-resistant and
methicillin-sensitive strains of Staphylococcus aureus was studied by Shibata et al.
(2005) and found that it enhanced the activity of the antibiotic. This synergistic
effect of the alkyl gallates is specific for β-lactam antibiotics, and it does not cause
any change in the effectiveness of other classes of antibiotics tested.
Another remarkable study was conducted on the effect of 5- methoxyhydnocarpin,
a compound isolated from chaulmoogra oil, on the activity of berberine (Stermitz
et al. 2000), and the results indicated that 5-methoxyhydnocarpin enhanced the
action of berberine against Staphylococcus aureus even though it did not show any
antimicrobial activity on its own. It is observed that the accumulation level of berberine in the cells increased sharply in the presence of 5-methoxyhydnocarpin,
allowing this natural product to deactivate the mechanism of bacterial resistance
against berberine. In the absence of 5-methoxyhydnocarpin, berberine is easily
extruded by the multidrug resistance pumps of Staphylococcus aureus. This indicates the potential use of a weak antimicrobial natural compound along with another
compound to intensify its activity (Ríos and Recio 2005). Table 11.1 gives a combination of natural products and synthetic drugs used to combat fungal infections.
11.5 Antiviral Compounds
Plants have enormous biosynthetic capacity, and the complexity of their bioactive
constituents seems to provide a rich source of natural compounds that may serve as
excellent phytotherapeutic agents (Schmidt et al. 2008). The development of antimicrobial drugs that are plant derived has not progressed, especially, in the case of
antiviral chemotherapy as compared to antifungal and antibacterial due to the
R. Reghu et al.