Plant Extracts That May Fight Bacteria and Antibiotic Resistance
A Worrying Problem and a Possible Solution
The increasing resistance of disease-causing bacteria to antibiotics is very worrying. Researchers say that it may not be long before people die from previously treatable diseases. Antibiotics are produced by bacteria and fungi or are made synthetically. One potential solution to the problem might be the use of specific chemicals in plants to fight harmful bacteria.
Scientists have recently made some interesting and perhaps very significant discoveries about the effects of certain plant extracts on dangerous bacteria. In the lab, the extracts either enabled antibiotics to work better or hindered the growth of bacterial populations. The extracts came from cranberries and from three plants that were used to make medicines during the US Civil War.
In this article I describe:
- antibiotic resistance,
- the plants that provided the helpful extracts,
- the harmful bacteria that were tested,
- and the experiments involving the organisms.
Antibiotics and Resistance
Antibiotics are chemicals made by bacteria or fungi to fight other organisms in their environment. Most antibiotics used in medicine come from (or originally came from) microbes. A small number were created in the laboratory instead of originating in living things. The drugs have proved very useful in fighting disease-causing bacteria that are dangerous for us.
The development of resistance to the effects of antibiotics is a natural phenomenon in bacteria. Human actions have made the process worse, however. We use the medications in excessive amounts and in situations where they aren't needed. They are widely used in agriculture to promote animal growth and prevent infections caused by living conditions, for example. In addition, they are sometimes prescribed for viral infections. Antibiotics don't affect viruses.
If a doctor prescribes an antibiotic for a bacterial infection, the patient should follow the medication instructions very carefully. Doses shouldn't be missed and the medication should be taken for the prescribed time. If a patient has questions about their prescription, they should consult their doctor or pharmacist.
Development of Antibiotic Resistance
As in other living things, the bacteria in a species are genetically similar but not identical. Gene variants give them slightly different features. Some bacteria in a group may have a variant or variants that give them resistance to a specific antibiotic. The resistant bacteria survive the antibiotic attack and (if they aren't destroyed in some other way) pass their helpful gene variants to some of their offspring.
As this process repeats from one generation to the next, the bacteria that are susceptible to the antibiotic's effects die and the resistant bacteria form a greater proportion of the population. Eventually, the population is composed almost entirely of resistant bacteria. This means that an antibiotic that once killed the species (or strain) no longer works. The video below describes the development of antibiotic resistance in bacteria in more detail. The process is sometimes known as multidrug resistance or antimicrobial resistance
Cranberries and Urinary Tract Infections
Cranberries are an acidic fruit with a tangy taste. When sweetened and used in a sauce, the red berries are very popular in North America. The sauce is a traditional accompaniment to turkey in a Christmas dinner. The berries are added to cakes, quick or dessert breads, and pies. Sweetened cranberry juice is popular. The juice can be bought in an unsweetened form as well.
Cranberry juice has had a reputation for preventing urinary tract infections (UTIs) for some time. Overall, scientific research into the validity of this idea has produced inconclusive results. It's thought that components of the juice may prevent the attachment of bacteria to the lining of the urinary tract in some people.
If you plan to drink cranberry juice regularly in an attempt to prevent a UTI, it might be a good idea to discuss the plan with your doctor. Though the juice is safe to drink, it may not be suitable for everyone, as the relevant link in the "References" section below describes.
Three Harmful Bacteria
Three species of bacteria were used in the cranberry extract experiment. They are all classified as gram-negative bacteria. These organisms have a more complex outer covering, or cell wall, than gram-positive bacteria. The terms "gram negative" and "gram positive" refer to the colour changes of the wall in a particular staining technique. The technique was created by a bacteriologist named Hans Christian Gram (1853–1938).
Proteus mirabilis can infect the urinary system and causes problems such as kidney stones and urinary tract infections. It's known for its swarming ability, or the ability to move over a surface in a large group.
Pseudomonas aeruginosa is resistant to multiple drugs and can cause potentially serious infections, including pneumonia. It survives well on moist surfaces such as medical catheters. It can be a special problem for people with cystic fibrosis.
Escherichia coli exists in many strains. The members of a bacterial strain have slightly different genetic compositions from other strains in the species. The differences may be significant as far as human health is concerned. Some strains of E. coli are harmless or even beneficial for humans. Others are harmful. Some cause gastrointestinal problems. Others cause urinary tract infections.
The Cranberry Extract Experiment
When scientists treat the three bacteria named above with an antibiotic, the microbes gradually develop resistance. When researchers at McGill University in Canada treated the bacteria with an antibiotic and cranberry extract, however, the microbes didn't develop resistance.
The scientists found that the extract increased the antibiotic's ability to fight bacteria in two ways. It caused the cell wall of the bacteria to become more permeable to the antibiotic, enabling a larger quantity of the drug to enter the microbes. At the same time, the bacteria had a harder time pumping the antibiotic out of the cell when the extract was present. The efflux pump in bacteria transports specific substances through the cell wall to the outside. The process is one way in which the microbes prevent antibiotics from hurting them.
The tree shown above is known as the Keeler Oak. It's located in New Jersey and is thought to have been planted around 1650. Extracts from the white oak, the tulip tree, and the devil's walking stick have been tested for their effects on bacteria.
The white oak (Quercus alba) has a wide distribution in North America. It's found mainly in the eastern and central part of the United States. Its northern distribution reaches southern Ontario in Canada. In the south, it reaches the northern tip of Florida.
The tree can live for several hundred years and is sometimes an impressive sight in its mature form. According to the Missouri Botanical Garden, it can be as tall as eighty feet in cultivation and up to a hundred feet tall in the wild.
As in other species of oak, the tree's leaves have deep lobes with a rounded tip and the fruit is an acorn. The leaves sometimes turn a beautiful red colour in the fall. The plant's species name means "white". The word refers to the light grey colour of the bark.
The tulip tree, tuliptree, or tulip poplar has the scientific name Liriodendron tulipifera. It's native to the eastern part of the United States. Like tulips, the tree blooms in the spring. The attractive and showy flowers are a mixture of orange, yellow, and green. They look somewhat like a tulip flower when viewed at the correct angle. A photo of a flower is shown at the start of this article.
Tulip trees belong to the magnolia family. They are tall and can potentially reach a height of ninety feet. The leaves are flat and lobed. They have an unusual notch shape at their tip. The seeds are born in an elongated cone-like structure.
Devil's Walking Stick
Devil's walking stick is a shrub or small tree with the scientific name Aralia spinosa. Its common name comes from the sharp spines on the branches, stems, and leaf stalks (petioles). The tree usually grows as a tall shrub up to fifteen feet high but occasionally grows as a tree that may be as tall as thirty-five feet. Like the two plants described above, it's native to the eastern part of the United States.
The flowers of the plant are white and small, but they are borne in large and very noticeable groups known as panicles. A panicle is often described as a branching cluster of flowers. The plant produces black berries.
Three Multidrug-Resistant Bacteria
The plant extract experiment was performed by scientists at Emory University in the state of Georgia. The scientists used three species of bacteria in their research. All of the species are associated with wounds as well as other problems in the body and are resistant to multiple drugs.
Acinetobacter baumannii is a short, rod-shaped bacterium. It's considered to be an opportunistic pathogen, or one that isn't always dangerous but takes advantage of a suitable environment in order to cause disease. One place where this environment may be found is in someone whose immune system isn't working properly. Another is in wounds. The bacterium is becoming increasingly important in hospitals. It has created problems in both military hospitals and civilian ones.
Staphylococcus aureus lives on the skin of many people and often causes no problems. Like the bacterium mentioned above, however, it's an opportunistic pathogen and can cause skin infections. Some strains of S. aureus are resistant to multiple drugs. One of these is MRSA, or methicillin-resistant Staphylococcus aureus. It's resistant to other antibiotics besides methicillin.
Klebsiella pneumoniae is another bacterium that sometimes exists on or even in the body without causing problems. It can be dangerous if it enters the lungs, however. As its name suggests, it can cause pneumonia. The bacterium is becoming potentially dangerous in hospital infections and can infect wounds.
It's important that we as individuals take antibiotics when they are prescribed and necessary. The medications are often essential and can save lives. Society as a whole is overusing them, however.
A Potentially Important Civil War Book
During America's Civil war (1861–1865), the Confederate Surgeon General commissioned a book about traditional plant medicines in the area. Conventional medicines were becoming hard to obtain at the time and infected wounds were becoming a big problem. The name of the commissioned book was Resources of the Southern Shield and Forests. It was compiled by Francis Porcher, who was a botanist and a surgeon.
Porcher's book mentioned thirty-seven plants that were traditionally believed to be effective for treating infected wounds. Emory University researchers chose three of them for their experiment, at least partly because the plants grew on a preserve on the university's campus.
The researchers followed the instructions in Porcher's book to make the extracts. The white oak extract was made from the tree's bark and galls, the tulip tree one from the plant's leaves, branch bark, and inner bark of the roots, and the devil's walking stick one from the shrub's leaves.
Galls are swellings or bumps on plants produced due to the presence of parasites in the area. Examples of parasites that trigger gall production include bacteria, fungi, viruses, and insects. A study of the chemicals in different types of galls and their effects on microbes might be very worthwhile.
Biofilms and Quorum Sensing in Bacteria
The discoveries made by the Emory University researchers involved effects of the plant extracts on biofilms and quorum sensing in bacteria. Many bacteria attach to a surface and live in a group surrounded by a protective film that they secrete. The film is known as a biofilm. Its existence makes the bacteria much harder to attack by antibiotics than planktonic bacteria (bacterial cells not attached to a surface or surrounded by a film).
One fascinating ability of bacteria is known as quorum sensing. This is a communication method between individual bacteria that's based on the concentration of specific chemicals in the environment. When the bacterial population is low, the concentration of a signaling molecule (also called an autoinducer) that the microbes release into the environment is also low. As the number of bacteria increase, the concentration of the autoinducer also increases.
Eventually the concentration of the autoinducer reaches a critical or threshold level, causing all of the bacteria in the area to perform a specific behaviour at the same time. A "quorum" has been reached. One of the behaviours triggered by quorum sensing is the formation of a biofilm. Other are behaviours that harm the host.
The Plant Extract Experiment
The Emory University scientists made the following discoveries in their experiment.
- The white oak extract inhibited the growth of S. aureus and prevented it from forming biofilms.
- The extract also inhibited the growth of A. baumannii and K. pneumoniae.
- The tulip tree extract inhibited the growth of S. aureus and prevented it from forming biofilms.
- The devil's walking stick extract inhibited the formation of biofilms in S. aureus and also inhibited quorum sensing in the bacterium.
The researchers found that the plant extracts interfered with the lives of the bacteria and the growth of their population. They didn't kill the bacteria, though. As the researcher in the quote below says, that doesn't mean that we should ignore the potential effects of the extracts in living things. In this age of antibiotic resistance, we need all the help that we can get.
Traditional plant remedies are often dismissed if they don't actively attack and kill pathogens. There are many more ways to help cure infections, and we need to focus on them in the era of drug-resistant bacteria.— Cassandra Quave, Emory University
Antibiotics in the Future
We badly need solutions for the problem of antibiotic resistance. The recent World Health Organization report about antibiotic resistance referenced below contains some worrying information. The report predicts that if antibiotic resistance continues to increase, humanity will experience ten million deaths a year by 2050.
The experiments described in this article could be very important. They were performed in lab equipment and in the case of the cranberry extract in insects as well. The results may or may not be the same inside the human body. The traditional use of cranberries to hinder UTI bacteria as well as the traditional use of the other plant extracts during the time of the Civil War offer hope. More research is needed, though. I hope this research is performed soon.
We badly need new ways to fight the bacteria that make us ill. Scientists are searching for new antibiotics and are having some success. Discoveries are occurring slowly, however, and their significance is not fully known. Perhaps a specific plant extract or multiple extracts acting alone or in combination with another factor will help to stem the tide of advancing antibiotic resistance.
- Antibiotic resistance information from the CDC (Centers for Disease Control and Prevention)
- No Time to Wait: Securing the Future From Drug-Resistant Infections from WHO (the World Health Organization)
- Cranberry juice and urinary tract infections from WebMD
- Cranberries help antibiotics to fight bacteria from the phys.org news service
- Quercus alba information from the Missouri Botanical Garden
- Facts about the tulip tree from the Morton Botanical Garden
- Information about the devil's walking stick from the Missouri Botanical Garden
- Three plants from Civil War medicine fight drug-resistant bacteria in the lab from the ScienceDaily news service
This content is accurate and true to the best of the author’s knowledge and does not substitute for diagnosis, prognosis, treatment, prescription, and/or dietary advice from a licensed health professional. Drugs, supplements, and natural remedies may have dangerous side effects. If pregnant or nursing, consult with a qualified provider on an individual basis. Seek immediate help if you are experiencing a medical emergency.
© 2019 Linda Crampton