Lipids and Essential Oils as Antimicrobial Agents E-Book

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 761

Veröffentlichungsjahr: 2010

Beschreibung

Lipids and essential oils have strong antimicrobial properties — they kill or inhibit the growth of microbes such as bacteria, fungi, or viruses. They are being studied for use in the prevention and treatment of infections, as potential disinfectants, and for their preservative and antimicrobial properties when formulated as pharmaceuticals, in food products, and in cosmetics.

Lipids and Essential Oils as Antimicrobial Agents is a comprehensive review of the scientific knowledge in this field. International experts provide summaries on:

• the chemical and biological properties of lipids and essential oils
• use of lipids and essential oils in pharmaceuticals, cosmetics and health foods
• antimicrobial effects of lipids
• in vivo and in vitro
• antimicrobial lipids in milk
• antimicrobial lipids of the skin
• antibacterial lipids as sanitizers and disinfectants
• antibacterial, antifungal, and antiviral activities of essential oils
• antimicrobial lipids in milk
• antimicrobial lipids of the skin
• antibacterial lipids as sanitizers and disinfectants
• antibacterial, antifungal, and antiviral activities of essential oils

Lipids and Essential Oils as Antimicrobial Agents is an essential guide to this important topic for researchers and advanced students in academia and research working in pharmaceutical, cosmetic and food sciences, biochemistry and natural products chemistry, microbiology; and for health care scientists and professionals working in the fields of public health and infectious diseases. It will also be of interest to anyone concerned about health issues and particularly to those who are conscious of the benefits of health food and natural products.

Leseprobe

Contents

Cover

Half Title Page

Title Page

Copyright

List of Contributors

Introduction

1: Membranes as Targets of Antimicrobial Lipids

1.1 Introduction

1.2 Oil and Water Don't Mix!

1.3 Polar Lipids

1.4 Properties of Surfactants

1.5 Cell Membranes

1.6 The Action of Antimicrobial Lipids on Cell Membranes

1.7 Conclusions

Acknowledgements

2: Antibacterial Effects of Lipids: Historical Review (1881 to 1960)

2.1 Introduction

2.2 Antibacterial Activity of Soaps

2.3 Inhibition of Lipids and Serum Albumin against the Antibacterial Action of Soaps

2.4 Diverse Actions of Fatty Acids and Their Salts on Bacteria

2.5 The Nature of the Bactericidal Action of Fatty Acids

2.6 A Possible Role of Soaps and Fatty Acids in Host Defence against Bacteria

2.7 Studies of Prophylactic and Therapeutic Applications of Soaps and Fatty Acids

2.8 Conclusions

3: Antibacterial, Antiviral and Antifungal Activities of Lipids

3.1 Introduction

3.2 Antibacterial Activities of Fatty Acids and Monoglycerides

3.3 Antiviral Activities of Fatty Alcohols, Fatty Acids and Monoglycerides

3.4 Antifungal Activities of Fatty Acids and Monoglycerides

3.5 Conclusions

4: Antimicrobial Lipids in Milk

4.1 Introduction

4.2 Occurrence

4.3 Molecular Properties

4.4 Antimicrobial Activity

4.5 Applications

4.6 Safety, Tolerance and Efficacy

4.7 Conclusions

5: Antimicrobial Lipids of the Skin and Tear Film

5.1 Introduction

5.2 Innate Immune Mechanisms in Skin

5.3 Types and Locations of Lipids of the Skin and Tear Film

5.4 Functions of Lipids

5.5 Antimicrobial Activity of Lipids and Their Mechanisms of Killing

5.6 Synergy of Cutaneous Lipids and Other Innate Immune Molecules

5.7 Lipids as Therapeutic Agents

5.8 Conclusions

Acknowledgments

6: Antimicrobial Lipids and Innate Immunity

6.1 Introduction

6.2 The Role of Human Milk Lipids in Innate Immunity

6.3 Antimicrobial Lipids in the Pulmonary Mucosa

6.4 Antimicrobial Skin Lipids

6.5 Conclusions

7: Lipids as Active Ingredients in Pharmaceuticals, Cosmetics and Health Foods

7.1 Introduction

7.2 Antimicrobial Effects of Lipids

7.3 Lipids in Pharmaceuticals

7.4 Microbicidal Lipids in Agriculture and Aquaculture

7.5 Lipids in Therapy

7.6 Lipids in Cosmetics

7.7 Lipids in Health Food

7.8 Conclusions

8: Antimicrobial Lipids as Disinfectants, Antiseptics and Sanitizers

8.1 Introduction

8.2 Soaps as Disinfectants and Antiseptics

8.3 Use of Bactericidal Lipids to Reduce Microbial Contamination of Food Products

8.4 Killing of Foodborne Bacteria by Glycerol Monocaprate (Monocaprin) Emulsions

8.5 Conclusions

9: Chemistry and Bioactivity of Essential Oils

9.1 Introduction

9.2 Chemistry of Essential Oils

9.3 Biological Activity of Essential Oils

9.4 Uses of Essential Oils

9.5 Conclusions

10: Antiviral Effects of Plant-Derived Essential Oils and Pure Oil Components

10.1 Introduction

10.2 Characterization and Medicinal Use of Essential Oils

10.3 Cytotoxicity of Essential Oils

10.4 Antiviral Activities of Essential oils

10.5 Mode of Antiviral Action of Essential Oils

10.6 Conclusions

11: Antibacterial and Antifungal Activities of Essential Oils

11.1 Introduction

11.2 Methods for Quantifying Antimicrobial Activity

11.3 Antibacterial and Antifungal Essential Oils by Plant Family

11.4 Antimicrobial Essential-Oil Components

11.5 Factors Influencing Activity

11.6 Mechanisms of Action

11.7 Clinical Efficacy of Essential Oils and Components

11.8 Toxicity of Essential Oils

11.9 Conclusions

Color Plates

Index

Lipids and Essential Oils as Antimicrobial Agents

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Library of Congress Cataloging-in-Publication Data

Lipids and essential oils as antimicrobial agents / editor, Halldor Thormar. p. ; cm. Includes bibliographical references and index. ISBN 978-0-470-74178-8 (cloth) – ISBN 978-0-470-97661-6 (ebook) – ISBN 978-0-470-97662-3 (obook) 1. Anti-infective agents. 2. Lipids–Therapeutic use. 3. Essences and essential oils–Therapeutic use. I. Thormar, Halldor. [DNLM: 1. Anti-Infective Agents. 2. Lipids–pharmacology. 3. Oils, Volatile–pharmacology. QV 250] RM267.L57 2011 615′.792–dc22 2010037014

A catalogue record for this book is available from the British Library.

Print ISBN: 9780470741788 eBook ISBN: 9780470976616 oBook ISBN: 9780470976623 ePub ISBN: 9780470976678

List of Contributors

Akram Astani Department of Infectious Diseases, Virology, University of Heidelberg, Heidelberg, Germany

Gudmundur Bergsson Institute of Molecular Medicine, Trinity College Dublin, Dublin, Ireland

Carol L. Bratt Dows Institute for Dental Research, College of Dentistry, The University of Iowa, Iowa City, IA, USA

Kim A. Brogden Dows Institute for Dental Research, and The Department of Periodontics, College of Dentistry, The University of Iowa, Iowa City, IA, USA

Christine F. Carson Discipline of Microbiology and Immunology (M502), School of Biomedical, Biomolecular and Chemical Sciences, The University of Western Australia, Crawley, Western Australia, Australia

Deborah V. Dawson Dows Institute for Dental Research, and The Department of Preventive and Community Dentistry, College of Dentistry, The University of Iowa, Iowa City, IA, USA

David Drake Dows Institute for Dental Research, and The Department of Endodontics, College of Dentistry, The University of Iowa, Iowa City, IA, USA

Katherine A. Hammer Discipline of Microbiology and Immunology (M502), School of Biomedical, Biomolecular and Chemical Sciences, The University of Western Australia, Crawley, Western Australia, Australia

Hilmar Hilmarsson Faculty of Life and Environmental Sciences, University of Iceland, Reykjavik, Iceland

Charles E. Isaacs Department of Developmental Biochemistry, New York State Institute for Basic Research in Developmental Disabilities, NY, USA

Thórdís Kristmundsdóttir Faculty of Pharmaceutical Sciences, University of Iceland, Reykjavik, Iceland

Peter J. Quinn Department of Biochemistry, King's College London, London, United Kingdom

Jürgen Reichling Department of Biology, Institute of Pharmacy and Molecular Biotechnology, University of Heidelberg, Heidelberg, Germany

Paul Schnitzler Department of Infectious Diseases, Virology, University of Heidelberg, Heidelberg, Germany

Skúli Skúlason Faculty of Pharmaceutical Sciences, University of Iceland, Reykjavik, Iceland

Halldor Thormar Faculty of Life and Environmental Sciences, University of Iceland, Reykjavik, Iceland

Phil Wertz Dows Institute for Dental Research, and The Department of Oral Pathology, Radiology & Medicine, College of Dentistry, The University of Iowa, Iowa City, IA, USA

Introduction

There has recently been a renewed interest in the antimicrobial effects of natural compounds which were commonly used as health remedies in the Western world until the advent of antibiotic drugs in the 1940s and 50s. After the emergence of antibiotics many previously fatal infections and infectious diseases were brought under control and millions of lives were saved. Due to the dramatic effect of the new synthetic drugs, some health professionals even believed that the threat to mankind of pathogenic microorganisms had finally been eliminated.

The great success of chemotherapy, using synthetic antibiotics against bacterial and fungal infections and nucleoside analogues against viral infections, discouraged researchers and the pharmaceutical industry from making serious efforts to develop drugs containing simple natural compounds. However, this may now be changing, with the increasing problem of drug-resistant bacterial and viral strains, partly caused by drug overuse. Because the development of new drugs has not in all cases kept up with the emergence of new resistant strains of pathogens, such strains cause thousands of deaths annually, many in hospitals. Also, most synthetic drugs have more or less severe side effects, which affect a considerable number of patients. In spite of these drawbacks, the health benefits of antibiotics to humans and their domestic animals can hardly be overestimated.

It has become apparent to many medical microbiologists and health professionals that besides synthetic drugs, which inhibit the replication of pathogenic microorganisms in a specific way, there may be a place for less specific antimicrobial compounds, microbicides, which kill the pathogens on contact. Microbicides could act in concert with specific antibiotics, launching a two-pronged attack on the invading pathogens. Direct killing, in addition to growth inhibition of pathogens, might make the formation of antibiotic-resistant strains less likely. Due to their broad antimicrobial actions, resistance to microbicides is rarely observed.

The success of antibiotic drugs is due to the fact that our knowledge of their actions is based on a solid scientific ground. Their actions are in most cases predictable and their side effects known, because they have undergone a thorough scientific scrutiny, for both safety and activity, before being applied to the general public. In contrast, the use of natural health remedies was for a long time mainly based on anecdotal evidence and on accumulated experience of their beneficial effects obtained over centuries. The knowledge was mostly empirical. Recently, and mostly during the past few decades, the antimicrobial actions of the natural compounds, which originate in both the animal and the plant kingdom, have been studied by modern scientific methods similar to those applied in the study of synthetic drugs. This research has confirmed and extended the prior empirical knowledge of their antimicrobial activity.

In this book, scientific studies of the antimicrobial actions of two groups of naturally occurring organic materials are reviewed, namely lipids and essential oils. Lipids are diverse constituents of plants and animals which are insoluble in water but soluble in nonpolar organic solvents such as ethanol and ether. The main types of lipid are fats and oils, phospholipids, waxes and steroids. These lipids have various functions in the body. Animal fats and vegetable oils are triglycerides composed of fatty acids and glycerol and are a source of energy. Phospholipid molecules contain two fatty acids and are a major component of cell membranes. The hydrolytic products of triglycerides and phospholipids, particularly the fatty acids, have antimicrobial activities. In addition to being natural compounds they have the advantage of being both environmentally safe and generally harmless to the body in concentrations which kill pathogenic microbes. They are nonallergenic and are fully metabolized in the body. Lipids, particularly triglycerides, are abundant in nature and are an inexpensive source of antimicrobial products.

The first part of this book deals with various aspects of lipids as antimicrobial agents, beginning with an examination of the chemical nature of lipids in Chapter 1. The history of lipids as antimicrobial agents, from the discovery of the antibacterial activity of natural soaps in the 1880s until 1960, is told in Chapter 2, followed by a discussion in Chapter 3 of more recent studies of the antibacterial, antiviral and antifungal actions of lipids. After chapters on antimicrobial lipids in mother's milk (Chapter 4) and the skin (Chapter 5), Chapter 6 looks at the role of lipids in the natural host defence against pathogenic microorganisms, discussed in the context of other factors of the innate immune system. Recent studies strongly support earlier observations that natural fatty acids on the surface of the skin and mucous membranes contribute significantly to the host defence against infections by pathogenic microbes. Triglycerides in breast milk are hydrolysed by lipases in the gastrointestinal tract of infants, where they release free fatty acids, which seem to have an important protective effect against enteric pathogens. It has been suggested that the natural protective function of lipids could be enhanced by prophylactive or therapeutic application of drugs containing lipids as active ingredients. Chapter 7 reviews the application of lipids in pharmaceuticals, cosmetics and health foods and their possible use in therapeutics. A broad overview is given not only of antimicrobial activity but also of other health-related functions of lipids. Finally, Chapter 8 discusses antimicrobial lipids as disinfectants, antiseptics and sanitizers, for example in the food industry and in the home. The advent of antibiotics and inexpensive, synthetic detergents in the middle of the twentieth century caused a decline of interest in common hygiene outside of the hospital setting, for example in the home and in public places such as schools. The problem of drug-resistant pathogens and of environmental hazards caused by some synthetic disinfectants has led to an awareness of the advantage of using natural and environmentally friendly disinfectants and sanitizers. Thus, antibacterial lipids could, for example, be used to reduce the risk of contamination by foodborne pathogens in the kitchen and in food-preparing and food-processing facilities.

Essential oils of flowering plants are secondary metabolites which are a part of the defence system of the plants, defending them against herbivorous animals and microorganisms. They have been used as health remedies for centuries but until recently little scientific research was carried out to establish the antimicrobial effect of essential oils and their chemical components. In the past few decades, a vast amount of scientific data has been collected on this subject and the second part of the book gives an overview of the current knowledge of the antimicrobial and biological functions of essential oils. Chapter 9 reviews the chemistry and bioactivity of essential oils and their use in food and cosmetic products. Chapter 10 describes the antiviral activity of essential oils and their effect in treatment of herpes simplex. Finally, Chapter 11 gives a comprehensive overview of the antibacterial and antifungal effects of essential oils, their use in pharmaceutical formulations and their clinical efficacy and toxicity in humans and animals.

Although focussing on the antimicrobial action of lipids and essential oils, the book also describes various other health-related aspects of these natural products. It thus gives comprehensive and detailed information on the biological effects of lipids and essential oils based on the results of scientific research. Each chapter stands by itself and need not be read in the context of the others. Therefore, the chapters do not have to be read in sequence starting at the beginning of the book. There is thus a certain degree of overlap of data between chapters, but not redundancy, since the same data are viewed from different points of view and in different contexts by the different authors. Although written by scientists and aimed primarily at health professionals, the book is written in language which should be understandable to readers in general. It should be of interest to anyone concerned about health issues and particularly to those who are conscious of the benefits of health food and natural products.

Halldor Thormar Reykjavik, June 2010

1

Membranes as Targets of Antimicrobial Lipids

Peter J. Quinn

Department of Biochemistry, King's College London, London, United Kingdom

1.1 Introduction

1.2 Oil and Water Don't Mix!

1.3 Polar Lipids

1.3.1 The Amphiphilic Character of Polar Lipids

1.3.2 Hydrophobic Constituents of Lipids

1.3.3 Polar Groups of Complex Lipids

1.4 Properties of Surfactants

1.4.1 Critical Micelle Concentration

1.4.2 Aggregation of Surface-Active Molecules

1.4.3 The Influence of Solvent

1.5 Cell Membranes

1.5.1 Membrane Lipids

1.5.2 Lipid Domains in Membranes

1.5.3 Membrane Proteins

1.5.4 Membrane Stability

1.5.4.1 Membrane Lipid Phase Behaviour

1.5.4.2 Membrane Lipid Homeostasis in Homoiothermic Organisms

1.5.4.3 Membrane Lipid Adaption in Poikilothermic Organisms

1.6 The Action of Antimicrobial Lipids on Cell Membranes

1.7 Conclusions

1.1 Introduction

Certain lipid. s are known to inhibit growth or kill microbe. s. A wide variety of lipids have been tested and they vary widely in chemical structure and efficacy. Because of the lack of a systematic relationship between lipid structure and antimicrobial activity an explanation of their mode of action is problematic. The two possible molecular mechanisms to account for the antimicrobial action of lipids are 1) a specific interaction with sites within the microorganism. that influences biochemical functions and loss of viability or 2) a general nonspecific interaction that perturbs the structure of the microorganism, thereby inhibiting normal physiological functions.

Lipids are a diverse class of compounds that defy definition by simple chemical characteristics but can be broadly categorized by their solubility in solvents of relatively low polarity. In this way they can be readily distinguished from the other constituents of living cells, such as nucleic acid. s, carbohydrate. s and protein. s. Indeed, this is the operational basis for the extraction and purification of lipids from biological tissues. The conventional methods of lipid extraction employ solvent mixtures with a relatively polar solvent, initially to loosen up the tissue and dislodge lipids from their interaction with other cellular constituents and culminate in isolation of the lipids in a two-phase system in which the polar molecules partition into an aqueous phase [1,2].

Within the general class of lipids, subdivisions are recognized on the basis of their relative solubility in solvents of low polarity, or to put it another way, solubility in solvents of different polarities. Again, no systematic chemical criteria can be adopted to account for solubility of lipids in solvents of different polarities. However, polarity. of solvent. s can be defined by objective criteria [3,4] and solubility. of lipids in solvents can be measured by a variety of biophysical parameters.

This chapter will provide an account of lipid solubility in solvents of different polarities and explain the general chemical principles that govern this property. The relevance of lipid solubility to antimicrobial action will be discussed in the context of the role of lipids in the structure of cell membranes of living organisms and how these structures are disrupted by antimicrobial lipids.

1.2 Oil and Water Don't Mix!

We are all familiar with the old adage that oil does not mix with water. Equally, we know intuitively that if a drop of ink is placed in a beaker of water the ink will diffuse out from the concentrated drop, eventually distributing randomly throughout the aqueous phase. Both of these situations have expressions in the Law of Thermodynamics. , which states that all systems move to their state of lowest free energy, and in the cases we are considering, to a more random and chaotic state. The formulation is:

(1.1)

where ΔG is the change in free energy. of the system, ΔH is the change in heat. , T is the absolute temperature. and ΔS is the change in entropy. . The negative sign on the TΔS component signifies a spontaneous change from a more ordered to a disordered state.

At first sight there seems to be a contradiction in the two examples given above. The two-phase system of oil and water appears to be a perfectly ordered system, yet clearly this is the equilibrium position. To understand why this is the lowest free energy of the system we need to consider the consequences on the order of the molecules if we attempt to place oil into an aqueous environment. Oils are largely composed of hydrocarbon, and hydrocarbons are nonpolar, since they have electron distributions about the constituent atoms that are relatively even. By contrast, water is highly polar, with electrons attracted to the oxygen atom generating a surfeit of negative charge (a δ-negative charge. ) and creating a deficiency of negative charges (δ-positive charge. s) associated with the two hydrogen atoms. This is the basis of molecular polarity. When hydrocarbon. is exposed to water the molecules of water in contact with the hydrocarbon lose their freedom to interact with like polar water molecules and consequently become ordered. It is this molecular order that results in a decrease in entropy and a consequent increase in free energy of the system.

Lipids of biological origin are not composed purely of hydrocarbon, and constituent atoms like oxygen and nitrogen bring about an asymmetric distribution of electrons within the lipid molecule. This provides opportunities for polar interactions with water, thereby increasing the entropy of the system. We next consider the origin of polarity of biological lipids and the common chemical strategies used in nature to achieve a polar character.