Explainer: What is C. difficile? | Science News for Students

Explainer: What is C. difficile?

A severe — and often lethal — bacterial infection has risen from a rarity to a big problem
Oct 22, 2014 — 10:25 am EST
Clostridium difficile

These bacteria, called Clostridium difficile, can be deadly. Scientists have developed a new and effective treatment that uses beneficial bacteria found in the feces of healthy people. 

CDC/Janice Carr

Infections due to Clostridium difficile bacteria — known as C. diff — have become a global problem. They kill an estimated 14,000 people each year in the United States alone. That’s according to the Centers for Disease Control and Prevention, based in Atlanta, Ga. Although half of C. diff’s victims tend to be elderly, the germ can sicken anyone, even young children.

The disease causes fever, gut pain and severe, watery diarrhea. It tends to strike people who have been prescribed antibiotics for so long that the drugs have wiped out many of the good microbes in the patients’ guts. That leaves room for C. diff germs to move in and take over.

C. diff is not a new germ, but its level of threat to people is relatively new. In the mid-1990s, “we didn’t believe people died of this,” notes Sandra Dial. She’s a doctor and epidemiologist at Canada’s McGill University in Montreal. Back then, if people did die, “it was very unusual,” she told Science News. “Now,” she says, “unfortunately, it’s not unusual.”

C. diff has become such a threat because of two changes that have occurred in the past 10 to 15 years. Together, they have made the germ far more virulent, or capable of causing disease.

First, the germ underwent some mutations. These are changes to genes. Mutations are common and can occur for many reasons. Some changes may have no effect on how an organism functions. An example would be a mutation in a developing baby that transforms what would have been a blue-eyed individual into someone with brown eyes.

In other instances, a mutation can produce changes in the types or amounts of chemicals that an organism produces. In C. diff, such a mutation transformed the old-style bacteria into a new strain. While not a new species, a new strain will have new features. In the case of C. diff, this was the production of toxins, or poisons, that trigger diarrhea.

C. diff can now make three types of toxins. They’re known as A, B and binary types. Patients infected with the strain of bacteria that makes the binary toxin are most likely to develop severe diarrhea.

Initially, only a few cases of infection involved this binary-toxin version of C. diff. But over time, this strain has become responsible for more and more cases of disease.

The second change that occurred: A growing share of these especially toxic C. diff germs became resistant to antibiotics — medicines designed to kill them. That means the germs were morphing into a still worse strain, a type known as a superbug.

Many people who get a C. diff infection pick it up at a hospital or place where many sick people reside, such as a nursing home. Although antibiotics may initially appear to knock out the infection, the disease often returns. In the second or third waves of C. diff infections, antibiotics may be unable to kill off the germs. That’s one reason why doctors now choose to treat some of these hard-to-cure cases with microbes collected from healthy people. The source of those healthy microbes — feces.

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.

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

binary     Something having two parts, or something based on the number two.

Centers for Disease Control and Prevention, or CDC  An agency of the U.S. Department of Health and Human Services, CDC is charged with protecting public health and safety by working to control and prevent disease, injury and disabilities. It does this by investigating disease outbreaks, tracking exposures by Americans to infections and toxic chemicals, and regularly surveying diet and other habits among a representative cross-section of all Americans.

Clostridium difficile      A bacterium that releases a toxin, which attacks the lining of the intestines. It can trigger colitis and severe diarrhea — conditions that can kill. In just the United States, C. difficile infections kill an estimated 14,000 people each year.

epidemiologist  Like health detectives, these researchers figure out what causes a particular illness and how to limit its spread.

gene   (adj. genetic) 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.

gut  Colloquial term for an organism’s stomach and/or intestines. It is where food is broken down and absorbed for use by the rest of the body.

infection    A disease that can spread from one organism to another.

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.

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 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.

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

toxic  Poisonous or able to harm or kill cells, tissues or whole organisms. The measure of risk posed by such a poison is its toxicity

toxin  A poison produced by living organisms, such as germs, bees, spiders, poison ivy and snakes.

virulence  (in medicine) The potency of a virus, bacterium or other agent in causing infectious disease. Among a given species, some strains may cause disease with very little exposure (such as infection with a few cells). Less virulent strains may take massive exposures to create disease.


L.J. Brandt. Fecal Transplantation for the Treatment of Clostridium difficile InfectionGastroenterology & Hepatology. Vol. 8, March 2012, p. 191. 

Further Reading

N. Seppa. “Drug appears safe in children with C. difficile infections.” Science News. October 14, 2014.

E. Engelhaupt. “Introducing the first bank of feces.” Science News blog, February 12, 2014.

S. Ornes. “Mining medicine from poop.” Science News for Students. October 24, 2013.

B. Harder. “Flora horror: Hospitals struggle with a serious new gut microbe [C. difficile].” Science News, Vol. 169, Feb. 18, 2006, p. 104.

E. Sohn. “Gut germs to the rescue.” Science News for Students. June 26, 2003.

Centers for Disease Control and Prevention. Clostridium difficile infection.