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Bacterial Infections
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Infections

Bacterial Infections

Bacteria are microscopic, single-celled organisms that exist everywhere; while many are harmless or beneficial, some can cause infections that require medical treatment.

What are bacteria?

Bacteria are tiny organisms that have only one cell. Under a microscope, they look like balls, rods, or spirals. They can be found almost everywhere on Earth, and your body contains about 10 times more bacteria cells than human cells.

There are many different types of bacteria. Most types do not make you sick, and some are helpful. For example, "good" bacteria in your digestive system help you digest food, absorb vitamins and minerals, and protect you from illness. Bacteria are also used in the production of foods like yogurt and cheese.

However, some types, known as infectious bacteria, can cause illness. These bacteria can reproduce quickly in your body, damage tissues, or release toxins (poisons) that damage your cells. Examples include Streptococcus, Staphylococcus, and E. coli.

How do bacterial infections spread?

Bacterial infections can spread through several routes:

  • Breathing in droplets or particles exhaled by an infected person, or having them land on your mouth, nose, or eyes.
  • Touching contaminated surfaces or objects and then touching your mouth, nose, or eyes.
  • Cuts, scrapes, and skin-to-skin contact with an infected person.
  • Transmission from a pregnant parent to the baby during pregnancy.
  • Consuming contaminated food or water.
  • Bites from an infected insect or animal.
  • Sexual contact (vaginal, anal, or oral) with an infected person.

What are the treatments for bacterial infections?

While your immune system may be able to fight off some infections, others require treatment with antibiotics. It is important to follow the directions for antibiotics carefully. Overuse or misuse can lead to antibiotic resistance, where bacteria become resistant to the medication. This makes the bacteria harder to kill and can result in infections that are difficult or impossible to treat.

Can bacterial infections be prevented?

You can help prevent some bacterial infections by:

  • Getting recommended vaccines.
  • Maintaining good hygiene, such as washing your hands often and covering your mouth and nose when coughing or sneezing.
  • Paying attention to food safety.
  • Cleaning and disinfecting frequently touched surfaces.
  • Preventing insect bites by using EPA-registered insect repellent and wearing appropriate clothing (long pants, shirts, and socks) when traveling to high-risk areas.
  • Practicing safe sex by using a latex or polyurethane condom during sexual activity.
  • Avoiding close contact with people who are sick.

Frequently Asked Questions

No, stopping antibiotics early is a major contributor to antibiotic resistance. Even if you feel better, a significant number of bacteria may still be present. Stopping the medication allows the strongest, most resistant bacteria to survive and multiply, potentially causing the infection to return with greater severity and making future treatments more difficult. Always complete the full prescribed course unless a doctor explicitly instructs you to stop.
Common side effects include nausea, diarrhea, and yeast infections (such as thrush or vaginal yeast infections). While mild gastrointestinal upset is common, severe or bloody diarrhea, a rash, or difficulty breathing are signs of a serious adverse reaction or a C. diff infection and require immediate medical attention. Probiotics or yogurt may help maintain gut health during treatment, but consult your doctor before starting any supplements.
ntibiotic resistance is not something you can detect through symptoms alone, as the infection will simply fail to improve or may worsen despite taking the prescribed medication. If your symptoms do not begin to improve within 48 to 72 hours of starting antibiotics, or if they return after you finish the course, contact your doctor immediately. They may need to perform a culture to identify the specific bacteria and select a different, more effective antibiotic.
While a definitive diagnosis often requires testing, bacterial infections frequently present with a higher fever, localized pain or swelling, and the production of pus or thick, discolored mucus. Viral infections tend to cause more systemic symptoms like body aches, fatigue, and a runny nose, and often resolve on their own within a week. However, because symptoms can overlap significantly, a healthcare provider should evaluate you to determine if antibiotics are necessary.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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