Issue:
93
Page: 71-72
Lipids and Essential Oils as Antimicrobial Agents
HerbalGram.
2012; American Botanical Council
Lipids and Essential
Oils as Antimicrobial Agents by
Halldor Thormar (ed.). West Sussex, UK: Wiley; 2011. Hardcover; 315
pages. ISBN: 9780470741788. $145.00.
Oils are important for life.
They are composed of complex chemicals in liquid form. Fixed oils are composed
of lipids that are vital for the cell and functions of living organisms. The
main types of lipids are fats, oils, phospholipids, and steroids. Animal fats
and vegetable oils are known as triglycerides, which are composed of fatty
acids and glycerol. Phospholipids, the major components of cell membranes,
consist of 2 fatty acids. When triglycerides and phospholipids undergo a
chemical reaction known as hydrolysis, they produce fatty acids with
antimicrobial properties. These fatty acids are abundantly available in nature
and are essential for the body.
Essential oils consist of
volatile terpenoid and non-terpenoid constituents not essential for life functions,
but they have other useful properties. Terpenoids are composed of hydrocarbons
and a number of smaller units known as isoprene molecules. Essential oils can
be found in aromatic plants and are responsible for their fragrance. Unlike
fixed oils that are obtained by expression or solvent extraction from plant
materials such as seeds, essential oils are obtained by water or steam
distillation or expression in the case of citrus oils. In Lipids and
Essential Oils as Antimicrobial Agents, the authors examine both categories
of oils with a focus on their antimicrobial properties.
Lipids and Essential
Oils as Antimicrobial Agents consists
of 11 chapters ably written by experts in their respective fields. Each chapter
provides comprehensive and valuable information on various aspects of
antimicrobial lipids and essential oils in an easily digestible manner.
The first 8 chapters deal with various aspects of lipids
as antimicrobial agents beginning with the chemical aspects of lipids and their
actions on biological membranes. The first chapter is titled “Membranes as
Targets of Antimicrobial Lipids.” The author offers a brief but comprehensive
explanation of the physical and chemical properties of lipids and their
behavior and function in living cells. At certain concentrations,
surfactants—a class of molecules that acts on the surface of cells—can act as
detergents, breaking apart lipid membranes. The author concludes that
antimicrobial lipids act in a similar way to kill microorganisms.
In the following chapter,
the author discusses the history of antimicrobial lipids research from the
1880s to 1960, focusing mainly on the antimicrobial activity and life-saving
functions of soaps. Striking examples of antimicrobial soaps include the use of
oleate soaps on anthrax and cholera germs and chaulmoogra oil (Hydnocarpus
wightiana, Achariaceae) for treating leprosy. Skin lipids with oleic
acid and other long-chain fatty acids have been shown to possess
self-disinfecting activity on human skin and its appendages like hair, nails,
and earwax. Chapter 3 discusses the more recently discovered antibacterial,
antifungal, and antiviral activities of lipids. Monoglycerides such as
monolaurin and monocaprin and fatty acids like lauric and linolenic acids
demonstrate antibacterial activities against gram-positive bacteria genera such
as Staphylococci (Staphylococcaceae), Streptococci (Streptococcaceae),
and Bacilli (Bacillaceae), as well as Propionibacterium (Propionibacteriaceae),
a bacterium that causes acne. Capric, lauric, palmitoleic, and arachidonic
acids, monocaprin, monolaurin, and monopalmitolein were found to be active
against gram-negative bacteria such as Neisseria gonorrhoeae
(Neisseriaceae, which causes gonorrhea), Salmonella (Enterobacteriaceae),
and Escherichia coli (Enterobacteriaceae), mainly in acidic conditions.
While monocarpin and monolaurin did not show significant activity against E.
coli at 30oC and physiological pH, by increasing the temperature
to 50oC and lowering the pH,
remarkable antibacterial activity was observed, demonstrating that
acidic conditions remove the barriers in outer membranes of the cell wall and
allow lipids to access and saturate the cell, causing disintegration of the
membranes.
Antiviral, antimicrobial,
and antiprotozoal activities of fatty acids, fatty alcohols, and monoglycerides
are also reviewed. Antimicrobial lipids in human breastmilk are discussed in
Chapter 4. Milk lipids play and important role not only in nutrition but also
in the protection of suckling neonates from infections. Breastmilk, which
contains medium-chain saturated and long-chain unsaturated fatty acids and
their respective monoglycerides, has the ability to destabilize microbial
membranes. Their mechanism of action is explained in detail. The same issue is
also discussed from another perspective in Chapter 6, in the section, “The Role
of Human Milk Lipids in Innate Immunity,” where breast feeding is recommended
to enhance the immune systems of newborn babies.
In chapter 5, the author
deals with antimicrobial lipids of the skin and explains their molecular
mechanism of action. Complex mixtures of lipids on skin are seen as
contributing to localized natural immunity. Skin lipids have been shown to be
effective against gram-positive bacteria, gram-negative bacteria, and yeasts.
They appear to act through microbial plasma membranes and can enhance innate
immunity. Effects of antimicrobial lipids in pulmonary mucosa, respiratory
tract, in the lungs and on skin, and their role in natural immunity are also
discussed in detail.
Chapter 7 comprises a
compilation of practical aspects of lipids as active ingredients in
pharmaceuticals, cosmetics, and health foods. It was interesting to read that
lipids are sometimes used as animal feed supplements instead of antibiotics,
and that capric acid acts as an antimethanogenic in ruminant animals.
Agricultural applications of fatty acids are mentioned as well, with the author
noting that linolenic and linoleic acids
exhibited activity against pathogenic fungi tested, while oleic acid had
limited antifungal activity on certain fungi. The effects of lipids on a
variety of diseases are reviewed in this chapter as well. The final chapter on
lipids covers practical uses of antimicrobial lipids as disinfectants, antiseptics,
and sanitizers. The dawn of soaps as germicides and the renewed interest in
recent years in using antimicrobial fatty acids and monoglycerides to reduce
bacterial contamination of foodstuffs and as sanitizers or disinfectants are
discussed. The use of the lipid monocaprin either singly or in liquid soaps is
recommended as a strong microbicidal.
Essential oils are covered
in the final 3 chapters. Chapter 9 gives an overview of the chemistry and
biological activity of essential oils. The chemistry of monoterpenes,
sesquiterpenes, diterpenes, norterpenes, and phenylpropanoids as well as
sulfur- and nitrogen-containing essential oil constituents is described. It
would have been beneficial for the authors also to include non-terpenoid
volatile components like alkanes, alkenes, and their oxygenated derivatives:
benzenoids, fatty acids, and their esters as essential oil constituents. In
this chapter, the author also reviews antibacterial, antifungal, antiviral,
antiprotozoal, and anticancer properties associated with essential oils. Their
use in pharmaceuticals and foods also appears in this chapter.
Chapter 10 is devoted
specifically to the antiviral activities of essential oils and their
components. Essential oils are complex mixtures of volatile chemicals, some of
which may possess antimicrobial and/or antiviral activities. Microorganisms
cannot easily develop resistance to essential oils like they do to single
chemicals due to the compexity of their multicomponent chemistry. Therefore,
they are preferable to single components for antimicrobial and/or antiviral
effects. Lemon balm (Melissa officinalis, Lamiaceae) essential oil has
shown antiviral activity against the herpes simplex viruse. Essential oils of
chamomile (Matricaria recutita, Asteraceae), star anise (Illicium
verum, Schisandraceae), dwarf pine (Pinus mugo, Pinaceae), manuka (Leptospermum
scoparium, Myrtaceae), and tea tree (Melaleuca alternifolia, Myrtaceae)
were found to be promising potential antiviral agents as well. A controlled
clinical trial of a tea tree oil gel was found effective in the treatment of
human herpes labialis. A comprehensive review of the mechanisms and
practical aspects of antibacterial and antifungal activities of essential oils
is given in the final chapter.
I recommend this book for
scientists, researchers, and health professionals interested in
pharmaceuticals, cosmetics, natural products, oils, or nutrition. Students also
can benefit from the comprehensive reviews in order to understand and learn the
similar actions of these 2 diverse groups of natural chemicals.
—K.
Husnu Can Baser, PhD Professor
of Pharmacognosy Anadolu
University BadeBio
Biotechnology Ltd. Eskisehir,
Turkey
|