In 1928, Alexander Fleming discovered penicillin, the first of the modern antibiotics that would revolutionize medicine and save millions of lives. However, today we find a large number of bacteria that have stopped responding to antimicrobial drugs. We are talking about resistant bacteria, or even worse, multi-resistant, as we call them when they are insensitive to various antibiotics.
The number of resistant bacteria is spreading rapidly and increasing worldwide, making it one of the top ten public health threats, according to the World Health Organization. It is estimated that by 2050 this type of pathogen will cause more than 300 million premature deaths and losses of 100 billion dollars in the world economy.
It is obvious that there is an urgent need to find new remedies with mechanisms of action capable of stopping the resistance of these microorganisms. And plants are currently being postulated as a promising solution.
Essential oils: Much more than smell and taste
If we look back, we will see that the use of vegetables to fight bacteria is nothing new. Before the existence of refrigerators, hunting and fishing pieces were covered with rosemary or thyme, which allowed these foods to be preserved for longer in good conditions. Later they were removed, but there was always something left over, so both plants became part of many traditional meat and fish recipes.
Today there is scientific evidence that the essential oils contained in the leaves of both thyme and rosemary have antimicrobial activity. Essential oils are volatile substances that give odor and flavor to many plants, which makes them interesting for the pharmaceutical, cosmetic, food and perfume industries. Made up of complex mixtures of organic compounds called terpenes and phenylpropanoids (usually between 20 and 60 different substances), they also have antibacterial, antifungal, antiparasitic or even antiviral capacity.
Some of the substances that compose them, such as menthol, anethole or limonene, may be familiar to the reader. Although sometimes, the complete essential oil is more effective than the separate components, since they act synergistically.
These oils accumulate mainly in the leaves, in the case of mint or eucalyptus, and in the flowers, as in the case of roses or chamomile. But they can also be found in other parts of the plant: the bark (cinnamon), the log or trunk (sandalwood), the fruits (anise), the seeds (nutmeg) or the underground organs (ginger and vetiver).
As they are very irritating, they should always be used diluted and it is not normally convenient to administer them orally (we are referring to the isolated essential oil, not to the plant that contains it).
Properties of eucalyptus, thyme, celery, chamomile…
The scientific evidence of the antiseptic power of essential oils is very numerous, for which we are simply going to list a few examples:
- Eucalyptus essential oil- In addition to being antitussive and expectorant, it has antiseptic properties in the respiratory tract.
- Components of the essential oil of the tea tree, some species of lavender or eucalyptus- Bactericidal activity against multi-resistant bacteria.
- Essential oil of some species of thyme and celery- Attacks the bacterium Helicobacter pylori.
- Oregano essential oil- Effective for hand hygiene
- Sandalwood or chamomile essential oil- Useful for foot hygiene and odor
- Lemon, sage, thyme or lavender essential oil- Surface disinfection
Other compounds of interest:
Plants have a veritable chemical arsenal against different types of threats. We must take into account that they cannot move and, therefore, they defend themselves with different compounds –called secondary metabolites– against intense solar radiation, extreme cold or heat, the attack of insects or pathogenic microorganisms, the pressure of herbivores, etc
Essential oils are an example of secondary metabolites. But plants synthesize many more that sometimes also have antimicrobial activity, such as alkaloids, flavonoids, lignans, stilbenes, tannins, coumarins, and other phenols.
This is the case of the components of burdock or dragon’s blood –active not only against bacteria, but also against some viruses–, garlic –due to its content in compounds rich in sulfur–, pepper or sundew, a carnivorous plant. The mechanisms by which these compounds slow down bacterial growth or directly kill pathogens are very diverse. This is the main reason why secondary metabolites are postulated as promising agents to develop new drugs against the growing resistance to antibiotics.
Throughout its history, man has used medicinal plants to treat different diseases. Today, the plant kingdom and its derived products could offer a solution to the rapid expansion of bacteria immune to antimicrobial drugs.
