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Overview of Bacteria


The Manual's Editorial Staff

Reviewed/Revised Feb 2024
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What are bacteria?

Bacteria are tiny living organisms. They're so small they can't be seen without a microscope. A human hair is 100 times wider than many common bacteria. Bacteria are not the same as other microscopic organisms such as viruses Overview of Viral Infections or fungi Overview of Fungal Infections Fungi are living organisms, but they are not plants or animals. All living things are divided into categories called kingdoms, and fungi have their own kingdom. Some fungi cause infections in... read more .

There are thousands of different kinds of bacteria. Bacteria have many different shapes, which helps doctors identify them.

Bacteria live almost everywhere, including:

  • In the ground

  • In the water

  • On your skin

  • Inside your mouth, intestines, and vagina

Bacteria reproduce very quickly when they have the right conditions. A few bacteria can become billions of bacteria within a day.

What is a bacterial infection?

A bacterial infection is when bacteria invade part of your body and make you sick. Common bacterial infections include:

Some bacteria release chemical poisons called toxins. Toxins can spread through your body and affect areas that the bacteria haven't invaded. Diseases caused by bacterial toxins include:

Do all bacteria make you sick?

No, many bacteria don't cause infection. Some bacteria are even helpful. Many of the bacteria that live on your skin or in your body are normal and don't hurt you. These are called your resident flora Resident Flora Healthy people live in harmony with most of the microorganisms that establish themselves on or in (colonize) nonsterile parts of the body, such as the skin, nose, mouth, throat, large intestine... read more . However, other bacteria that get on or in your body can attack it.

How do you get a bacterial infection?

Harmful bacteria can get in your body in different ways. You can:

  • Eat or drink something with bacteria in it

  • Breathe air that's carrying bacteria

  • Touch something contaminated with bacteria and then touch your mouth, nose, or eyes

  • Get a cut, scrape, or burn that lets bacteria into your skin

Some harmful bacteria, such as those that cause tetanus, come from the environment. However, most harmful bacteria come from people or sometimes animals that have an infection.

Sometimes the normal bacteria in your body get in the wrong place. For example, the normal bacteria in your intestines can cause an infection if they get into your bladder or your bloodstream.

How does your body defend itself against bacteria?

How do doctors know you have a bacterial infection?

Doctors suspect a bacterial infection based on your symptoms. They usually send a sample to the lab to test for bacteria. Depending on where the infection seems to be, they may send a sample of:

  • Blood

  • Urine

  • Sputum (mucus you cough up)

  • Swabs from your throat, penis, or vagina

The lab can tell the doctor if bacteria are present, what kind they are, and what kinds of antibiotics might kill them.

How do doctors treat a bacterial infection?

Your body may fight off some bacterial infections on its own. But for many bacterial infections, doctors give you:

Antibiotics, such as penicillin, are medicines that kill bacteria. There are many different antibiotics. Each antibiotic works against only certain bacteria.

If you have a serious bacterial infection, you may need to be in a hospital and get antibiotics directly into your vein (IV).

What is antibiotic resistance?

Antibiotic resistance means that a bacteria isn't able to be killed by a certain antibiotic.

Bacteria are naturally resistant to certain antibiotics. However, bacteria frequently become resistant to antibiotics that used to work well. They become resistant because their genes mutate or they acquire genes from other bacteria that have become resistant. They then pass these resistance genes on to their descendants.

Antibiotic resistance is a big problem. Resistant infections require more powerful antibiotics that often have serious side effects. Even with powerful antibiotics, thousands of people die from antibiotic-resistant infections every year.

The more often antibiotics are used, the more likely resistant bacteria are to develop. That means antibiotic resistance often develops in hospitals and also on some farms where animals are regularly given antibiotics. Resistant bacteria can spread from person to person. This spread is particularly dangerous in hospitals, where many people have a weak immune system Overview of the Immune System The immune system is your body's defense system. It helps protect you from illness and infection. The immune system's job is to attack things that don’t belong in your body, including: Germs... read more or are already seriously ill.

How can I prevent bacterial infection?

To prevent bacterial infections:

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