Mother koalas provide their babies with bacteria that allow them to digest eucalyptus leaves. (Marius Becker /Agence France-Presse via Getty Images )

As a pediatrician, I spend a lot of time looking for bacteria that might be making my patients sick. Some well-known illnesses that are caused by bacteria include strep throat, ear infections, Lyme disease and conjunctivitis (pinkeye). Bacteria are also responsible for acne, cavities and body odor.

Bacteria can hurt you in two ways. Some attack cells directly. Others produce toxins (poisons) that make you sick. Either way, bacteria can rapidly damage or destroy cells.

While it’s true that some bacteria can make you sick, most species of bacteria are helpful. Bacteria can be found everywhere. They live in water, in the air and on land. Bacteria are among the smallest life forms on the planet. If you lined up 10,000 staph bacteria, they would fit on the head of a pin. (The same pin could hold 1 million cold viruses.)

Here are some cool facts about bacteria.

● Bacteria are essential to life on Earth. Along with fungi, they decompose, or break down, dead plants and animals to provide nutrients for plant life. Some bacteria turn nitrogen from the atmosphere into nitrates that plants need for growth.

● Bacteria help lots of animals digest food while producing vitamins for the host animal. Baby koalas ingest pap, a mucuslike substance that contains billions of bacteria, from their mother’s poop at six months of age. The pap allows them to digest eucalyptus leaves. Termites wouldn’t be able to digest wood fiber if it weren’t for certain bacteria that live in their intestinal tract.

● One type of bacteria “eats” oil and can be used to help clean up oil spills, including the 2010 spill in the Gulf of Mexico.

● Sewage treatment plants use bacteria to help purify water.

● Bacteria are used to make food. They help turn milk into yogurt and cheese. The most expensive coffee in the world exists because of bacteria. There is a small, catlike animal in Indonesia that eats coffee beans as part of its diet. As the beans move through its intestine, bacteria remove some of the chemicals in the beans that make them bitter. When the animal poops, the beans are harvested, cleaned and made into coffee. (See if that doesn’t make your parents kick the caffeine habit!)

The reason you sometimes develop diarrhea after taking antibiotics is that the medicine kills the good bacteria in your intestinal tract as well as the bad ones that are making you sick. Killing the good bacteria hampers the way your large intestine works.

Eating good bacteria can help your digestion and treat diarrhea. Good bacteria are called probiotics. You can find them in certain yogurts and as food supplements.

So, yes, there are lots of “good” bacteria out there!

—Howard Bennett

Howard Bennett, a Washington pediatrician, is the author of “Harry Goes to the Hospital.