Teen studies how germs resist our drugs

Yutao Su, 18, remembers the first time antibiotics grabbed his attention. “It was a presentation I heard in my sophomore year of high school,” he says. The speaker described “how antibiotic use selects for a stronger next generation of bacteria.”

He was explaining antibiotic resistance.

When people get sick with bacterial infections, doctors prescribe medicines called antibiotics to kill the germs responsible. But bacteria reproduce fast. As they do, their genes — sections of DNA that contain instructions to make proteins — may become altered. That’s called a mutation. Some mutations may allow the bacteria to survive drugs meant to kill them. Scientists refer to this immunity as resistance.

Bacteria can trade genes back and forth. If they share the genes for antibiotic resistance, medicines may no longer work against disease-causing microbes. These tougher germs can just keep reproducing — making both their offspring cells and neighbors harder to kill. Doctors refer to these ultimate survivors as superbugs.

While a junior at Cedar Falls High School in Iowa, Yutao decided to study antibiotic resistance. He applied to the Secondary Student Training Program at the University of Iowa in Iowa City. This program puts high school students into labs on the university’s campus for a summer of research.

The teen ended up in the lab of Tara Smith. She studies bacteria. Smith is interested in resistance. After all, she notes, “My kids get sick sometimes.” And when a doctor prescribes them antibiotics “I want those drugs to work and cure them.”

Smith assigned Yutao to a project on zinc. Many antibiotics are based on compounds produced by organisms as a chemical defense. The famous antibiotic penicillin comes from a mold. But zinc is different. It’s a chemical element and a metal.  Yet it still has antimicrobial properties. That means it can kill bacteria. And those germs can develop resistance to zinc just as they do to antibiotics.

Farmers like to put antibiotics in the food of their farm animals. Sometimes they add zinc to the diet instead. Both materials prevent animals from picking up bacterial infections. Both also seem to make the animals grow faster. This means the animals are ready for market sooner. With animals going to market faster, the farmer can raise more animals and make more money in a shorter period of time. But giving antibiotics and antimicrobials to millions of farm animals ups the chances that bacteria will become resistant to these agents.

Yutao and Smith wanted to look at how germs resist zinc. If harmful bacteria become resistant to zinc, Smith wondered, would they also be resistant to other antibiotics?  Each type of resistance is the result of changes in a very specific gene. But, Smith notes “genes that allow bacteria to become resistant don’t work alone. They are often in groups, a line of genes all in a row.” Some genes reside together in little loops of DNA. Called plasmids, these loops can pass from germ to germ. So if a bug has genes resistant for one antibiotic, it often has nearby genes that can resist other germ-killers.

In Smith’s lab, Yutao helped to test 349 different samples of bacteria. He examined each type’s DNA. He looked for germs that were resistant to zinc. He also examined whether these same microbes were resistant to antibiotic drugs.

As part of a larger study run by Rajeshwari Nair and Dipendra Thapaliya at the University of Iowa, Yutao and Smith showed that germs resistant to zinc also have genes that resist drugs designed to take out bacteria. In particular, zinc resistance in Staphylococcus aureus bacteria often showed up along with resistance for the antibiotic methicillin. These methicillin-resistant Staphylococcus aureus (or MRSA) are particularly nasty bugs.

If zinc resistance genes accompany genes for drug resistance, it means zinc feed additives could reduce the usefulness of important germ-killing drugs. Now, if someone gets infected with a zinc-hardy germ, there may be fewer ways to knock out the infection it causes.

Yutao didn’t just help to find a new piece of the antibiotic-resistance puzzle. He also got his name as an author on the scientific paper that describes the findings. It was published September 15 in Infection Control and Hospital Epidemiology.

Smith says Yutao contributed much to the scientific paper. One reason: He came into the lab well prepared. “We told him about projects before he arrived, and he had read many of our papers,” she recalls. So when he came in, already “He had a lot of ideas.”

Understanding those papers and learning many of the scientific techniques it described proved challenging. But Yutao worked hard, he said, because “I was trying to fit into a group of people who knew so much more than I did” about antibiotics.

Now in college, he will be taking his studies further. A freshman at Washington University in St. Louis, Mo., he hopes to enter medical school.

*Tara Smith is a personal friend. You can follow her on Twitter at @aetiology.

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Power Words

antibiotic  A germ-killing substance prescribed as a medicine (or sometimes as a feed additive to promote the growth of livestock). It does not work against viruses.

antimicrobial    A substance used to kill or inhibit the growth of microbes. This includes naturally derived chemicals, such as many antibiotic medicines. It also includes synthetic chemical products, such as triclosan and triclocarban. Manufacturers have added some antimicrobials — especially triclosan — to a range of sponges, soaps and other household products to deter the growth of germs.

bacterium (plural bacteria)  A single-celled organism forming one of the three domains of life. These dwell nearly everywhere on Earth, from the bottom of the sea to inside animals.  

DNA  (short for deoxyribonucleic acid) A long, spiral-shaped molecule inside most living cells that carries genetic instructions. In all living things, from plants and animals to microbes, these instructions tell cells which molecules to make.

evolution    A process by which species undergo changes over time, usually through genetic variation and natural selection, that leave a new type of organism better suited for its environment than the earlier type. The newer type is not necessarily more “advanced,” just better adapted to the conditions in which it developed.

fungus  (plural: fungi) Any of a group of unicellular or multicellular, spore-producing organisms that feed on organic matter, both living and decaying. Molds, yeast and mushrooms are all types of fungi.

gene  A segment of DNA that codes, or holds instructions, for producing a protein. Offspring inherit genes from their parents. Genes influence how an organism looks and behaves.

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

growth promoter    (in livestock agriculture) A medicine, usually an antibiotic, added in small doses to the feed given to animals raised for meat. Used as a preventive medicine, it can reduce the risk that animals will become sick, which would slow their growth. And that would decrease a farmer’s profits.

infection  A disease that can be transmitted between organisms.

livestock   Animals raised for meat or dairy products, including cattle, sheep, goats, pigs, chickens and geese.

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.

mutation  Some change that occurs to a gene in an organism’s DNA. Some mutations occur naturally. Others can be triggered by outside factors, such as pollution, radiation, medicines or something in the diet. A gene with this change is referred to as a mutant.

penicillin     The first antibiotic (although not the first one used on people), it’s a natural product that comes from a mold.

plasmid  A small circular loop of DNA that is separate from the main chromosomal DNA of bacteria.

resistance  (as in drug resistance) The reduction in the effectiveness of a drug to cure a disease, usually a microbial infection. (as in disease resistance) The ability of an organism to fight off disease.

superbug   A popular term for a disease-causing germ that can withstand medicines.