Plant extract mutes germs to fight infections | Science News for Students

Plant extract mutes germs to fight infections

An extract from leaves keeps bacteria from sensing how plentiful they are — and turning harmful
Jun 2, 2017 — 12:58 pm EST
extract vials

An extract from dried leaves of the sweet chestnut (Castanea sativa), a tree native to Europe and Asia, could help fight the development of nasty bladder infections.

D. Thapa

LOS ANGELES, Calif. — Some bacteria have alter egos. In small numbers, they pose no harm. But once they form a large crowd, they can turn into an aggressive, disease-causing mob. This doesn’t have to happen, however. The extract of a common plant could short-circuit this transformation, a teen’s research now finds. The extract confuses the germs so that they never realize how numerous they are.

Devina Thapa, 17, of the Academy of Science in Sterling, Va., described her new research here, last month, at the Intel International Science and Engineering Fair.

The teen harnessed a plant product to deter infection by germs that pose a risk to the body’s urinary tract. That system includes the bladder (a hollow organ that stores urine until you’re ready to pee). Each year, millions of people contract urinary tract infections (UTIs). And roughly four in every five of those UTIs, Devina notes, seem to stem from medical use of a tube to drain urine from the bladder. That tubing is known as a catheter (KATH-eh-tur).

urinary catheter
Catheters, like the one shown here, have been linked to most bladder infections. Incorporating a plant extract into the plastic-like tubing when its made might avoid that problem, a teen’s study finds.

People need catheters for a variety of reasons, most of them related to being unable to control their bladder. Patients may need a catheter if they have blockages such as bladder stones or kidney stones. Certain medications make it difficult to urinate. Plus, some types of surgery can make it painful to pee. Overall, statistics suggest that between 15 and 25 percent of patients in the hospital get a catheter at some point in their stay. 

Catheters can pick up germs when they’re inserted into the body. One of the most common species they pick up is Staphylococcus epidermidis (STAF-ih-lo-KOK-us Ep-ih-DER-mih-dis). These bacteria take part of their name from where they live. Epidermis is the scientific name for the outer layer of skin. And on the skin, these microbes usually cause no harm. But inside the body, they find far friendlier growth conditions. It’s warm and moist, and they are protected. This permits the bacteria to multiply.

And when they proliferate into mobs, their behavior changes for the worse, says Devina. The germs send chemical signals to each other in a process called quorum sensing. Quorum (KWOR-um) comes from a Latin word. It’s defined as the minimum number of people needed at a meeting for decisions there to be considered official.

For her project, Devina wanted to see if she could interfere with the ability of S. epidermidis to form a gooey biofilm. Biofilms stick to surfaces, including catheters. The slimy film protects a community of germs, making it difficult for the body — or drugs — to kill. At present, says Devina, treatments that inhibit quorum sensing don’t seem to cause drug resistance. Drug resistance can arise with treatments that set out to kill bacteria. If some of the bacteria survive a treatment that kills most of them, they go on to reproduce. This can give rise to a strain of the germs that resists later treatment.

Researchers already know that plant extracts of the sweet chestnut tree interfere with quorum sensing among Staphylococcus germs. That tree species, Castanea sativa (CAS-tuh-nay-uh Sah-TEE-vah), grows from Europe to southwestern Asia. But Devina wondered if extracts of this plant would work if they were a part of the material used to make catheters. That tubing often is made from flexible polymers such as silicones, she notes. One common type is known as PDMS. That’s short for polydimethylsiloxane (PAH-lee-dye-METH-ill-sy-LOX-ayne).

ground up leaves
Devina ground up the plant leaves by hand before soaking them in alcohol to create an extract.
D. Thapa

So, Devina decided to make her own versions of PDMS that included the extracts. She purchased dried leaves, ground them up and soaked them in ethanol (a type of alcohol) for 24 hours. (That’s a common way to obtain plant extracts, she notes.) Then, she filtered out the leaves and collected the liquid. This was her extract. She diluted this extract with different amounts of water to make solutions that were between one-quarter and three-quarters as strong as the starting extract.

Finally, she molded small disks of PDMS. To do this, she purchased PDMS in liquid form, then added a hardener. She also added various amounts of her extract to this mix (before it solidified into a flexible rubberlike material). She also made PDMS disks that contained silver nanoparticles instead of her extract. Nanosilver is known to kill many types of germs. She mixed her materials in the weight ratio of 10:1:1. The first number represents the weight of PDMS liquid. The second number was the weight of the liquid needed to cure the PDMS into a flexible solid. The third number was weight of the added extract or nanosilver.

Devina made six different versions of her disks. One included the nanosilver. Four versions included the various strengths of plant extract. The final version, a control for the experiment, had water instead of the extract or nanosilver. Unlike the other treatments, that water form shouldn’t affect the bacteria.

Once they were cured, Devina placed her silicone disks in mixtures of urine and bacteria. Then, she heated those mixtures to 37° Celsius (98.6° Fahrenheit), which is body temperature. After incubating the disks in this environment for a while, she added a stain to the mix. It would glow in certain types of light if the bacteria had formed biofilms. The development of a biofilm would signal that the germs had amassed to mob status and could foster disease.

As expected, the PDMS disk that included silver nanoparticles stifled biofilm growth. The weakest solutions of the plant extract didn’t. Disks made with them became covered with the same amount of biofilm as had grown on the disks made with plain water. But disks made with stronger extracts were protected. Among disks made with the three-quarter strength extract, a biofilm only covered about 10 percent of the area covered on the untreated disk. The full strength extract cut the biofilm growth even more, to just 3 percent of what fouled the untreated disks.

These results hint that the plant extract could be used to retard bacterial growth in all sorts of PDMS medical devices, the teen now claims.

Maybe one of the best things about her treatment is that it costs so little. One gram of silver nanoparticles cost about $25, she notes. But a gram of her extract costs about 3 cents.

The 12th-grader’s project earned Devina a second-place award worth $1,500 from ISEF judges in the category of Translational Medical Science. ISEF was created by Society for Science & the Public and is sponsored by Intel. The competition lets students from around the world show off their winning science fair projects. (The Society also publishes Science News for Students.) This year, Devina was one of nearly 1,800 high school finalists from more than 75 countries who competed for big prizes and the ability to display their work.

Power Words

(more about Power Words)

aggressive     (n. aggressiveness) Quick to fight or argue, or forceful in making efforts to succeed or win.

bacteria     ( singular: bacterium ) Single-celled organisms. These dwell nearly everywhere on Earth, from the bottom of the sea to inside other living organisms (such as plants and animals).

behavior     The way something, often a person or other organism, acts towards others, or conducts itself.

biofilm     A gooey community of different types of microbes that essentially glues itself to some solid surface. Living in a biofilm is one way microbes protect themselves from stressful agents (such as poisons) in their environment.

bladder     A flexible bag-like structure for holding liquids. (in biology) The organ that collects urine until it will be excreted.

catheter     A thin tube used to drain a fluid from inside the body. Often made of flexible material, catheters can be either inserted temporarily or installed for a longer interval. Some of the most commonly used types are used to drain urine from the bladder, where the fluid is normally stored until urination. 

chemical     A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.

chemical signal     A message made up of molecules that get sent from one place to another. Bacteria and some animals use these signals to communicate.

control     A part of an experiment where there is no change from normal conditions. The control is essential to scientific experiments. It shows that any new effect is likely due only to the part of the test that a researcher has altered.

cure     (in manufacturing and chemistry) The process of finalizing some chemical process that makes a product or surface strong and useful. For instance, cement and paint may feel dry to the touch within an hour or two, but will not really be strong until they have fully cured (a process that may take another one or more days).

deter     An event, action or material that keeps something from happening. For instance, a visible pothole in the road will deter a driver from steering his car over it.

engineering     The field of research that uses math and science to solve practical problems.

environment     The sum of all of the things that exist around some organism or the process and the condition those things create. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature and humidity (or even the placement of components in some electronics system or product).

epidermis     The outermost layer of skin.

ethanol     A type of alcohol, also known as ethyl alcohol, that serves as the basis of alcoholic drinks, such as beer, wine and distilled spirits. It also is used as a fuel, often mixed with gasoline, for instance.

extract     (v.) To separate one chemical (or component of something) from a complex mix. (noun) A substance, often in concentrated form, that has been removed from its natural source. Extracts are often taken from plants (such as spearmint or lavender), flowers and buds (such as roses and cloves), fruit (such as lemons and oranges) or seeds and nuts (such as almonds and pistachios). Such extracts, sometimes used in cooking, often have very strong scents or flavors.

germ     Any one-celled microorganism, such as a bacterium or fungal species, or a virus particle. Some germs cause disease. Others can promote the health of more complex organisms, including birds and mammals. The health effects of most germs, however, remain unknown.

infection     A disease that can spread from one organism to another. It’s usually caused by some type of germ.

Intel International Science and Engineering Fair     (Intel ISEF) Initially launched in 1950, this competition is one of three created (and still run) by the Society for Science & the Public. Each year now, approximately 1,800 high school students from more than 75 countries, regions, and territories are awarded the opportunity to showcase their independent research at Intel ISEF and compete for an average of $4 million in prizes. 

microbe     Short for microorganism. A living thing that is too small to see with the unaided eye, including bacteria, some fungi and many other organisms such as amoebas. Most consist of a single cell.

nanoparticle     A small particle with dimensions measured in billionths of a meter.

organ     (in biology) Various parts of an organism that perform one or more particular functions. For instance, an ovary is an organ that makes eggs, the brain is an organ that makes sense of nerve signals and a plant’s roots are organs that take in nutrients and moisture.

polymer     A substance made from long chains of repeating groups of atoms. Manufactured polymers include nylon, polyvinyl chloride (better known as PVC) and many types of plastics. Natural polymers include rubber, silk and cellulose (found in plants and used to make paper, for example).

quorum sensing     The ability of organisms to gauge the presence of others of their kind, often through chemicals that the organisms produce and release into the environment. Once individuals recognize a certain number of organisms are close by, their behavior often changes. Bacteria can turn from benign to deadly, for example.

ratio     The relationship between two numbers or amounts. When written out, the numbers usually are separated by a colon, such as a 50:50. That would mean that for every 50 units of one thing (on the left) there would also be 50 units of another thing (represented by the number on the right).

risk     The chance or mathematical likelihood that some bad thing might happen. For instance, exposure to radiation poses a risk of cancer. Or the hazard — or peril — itself. (For instance: Among cancer risks that the people faced were radiation and drinking water tainted with arsenic.)

silicone     Heat-resistant substances that can be used in many different ways, including the rubber-like materials that provide a waterproof seal around windows and in aquariums. Some silicones serve as grease-like lubricants in cars and trucks. Most silicones, a type of molecule known as a polymer, are built around long chains of silicon and oxygen atoms.

strain     (in biology) Organisms that belong to the same species that share some small but definable characteristics. For example, biologists breed certain strains of mice that may have a particular susceptibility to disease. Certain bacteria or viruses may develop one or more mutations that turn them into a strain that is immune to the ordinarily lethal effect of one or more drugs.

tract     A particular, well-defined area. It can be a patch of land, such as the area on which a house is located. Or it can be a bit of real estate in the body. For instance, important parts of an animal’s body will include its respiratory tract (lungs and airways), reproductive tract (gonads and hormone systems important to reproduction) and gastro-intestinal tract (the stomach and intestines — or organs responsible for moving food, digesting it, absorbing it and eliminating wastes).


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Meeting: D. Thapa. Reinventing the catheter: Inhibiting UTIs by creating a novel material integrated with Castanea sativa to inhibit quorum sensing among nosocomial infection causing bacteria. Intel International Science and Engineering Fair. May 15, 2017. Los Angeles, Calif.

Further Reading

More about Intel ISEF: 

Welcome to Intel ISEF 2017.” May 16, 2017.

Intel ISEF 2017 begins.” May 15, 2017.