What to Know About Antibiotic Sensitivity Testing

‌Your doctor might order an antibiotic sensitivity test to find the best treatment for you when you have an infection. It helps determine both the appropriate antibiotic and dosage that you need to treat your infection. Here’s what you need to know.

Why Is Antibiotic Sensitivity Testing Done?

‌Antibiotic sensitivity testing is often done when you have an infection that may be resistant to antibiotics. This means that antibiotics are less effective or don't affect certain bacteria. This makes it more difficult to treat bacterial infections and illnesses. 

Here are some infections that may be antibiotic-resistant or are difficult to treat:

  • Tuberculosis 
  • Methicillin-resistant Staphylococcus aureus (MRSA)
  • Salmonella typhi or typhoid fever 
  • Clostridioides difficile or C. diff
  • Pneumonia

There are almost 3 million antibiotic-resistant infections every year. More than 35,000 people die from these infections.

Antibiotic sensitivity testing can help find suitable treatments for these antibiotic-resistant infections and prevent further complications.

What Causes Antibiotic Resistance?

Antibiotics are medicines that eliminate bacteria. Many antibiotics are designed to treat specific bacterial infections.

Over time, as antibiotics have been used more and more, many bacteria have adapted their genetic code to fight back. Resistant bacteria aren't killed by antibiotics. They survive to multiply and may pass on their resistance to other bacteria.

Overusing and misusing antibiotics can also lead to bacteria becoming resistant to antibiotics. To prevent antibiotic resistance, keep the following in mind:‌ 

Only take antibiotics when necessary. Illnesses caused by viruses, like a cold or flu, won't be affected by antibiotics.

Take antibiotics exactly as your doctor has prescribed. Even if you are feeling better, it's important to take all the antibiotics you are prescribed.

Don’t take leftover antibiotics. Antibiotics can't be used to treat all bacterial infections. You should only take antibiotics that are specifically prescribed for an infection.

Make an effort to avoid foodborne bacterial infections. Wash your hands while you cook and make sure all your food is safely cooked before eating them. 

Wash your hands regularly. Keeping your hands clean will help you avoid many bacterial infections.

When you have an antibiotic-resistant infection, it may be difficult to treat. You may have more serious side effects and it might take longer to recover. Antibiotic sensitivity testing can help your doctor find you a more effective treatment.

What Can You Expect During an Antibiotic Sensitivity Test?

Your doctor will take a sample from the infected area of your body. 

‌‌There are different kinds of samples that can be taken for the test: 

  • Blood cultures
  • Urine cultures
  • Wound cultures
  • Sputum cultures. They require that you either cough up sputum into a cup or be swabbed for a culture sample from your nose.  
  • Throat cultures. They require a swab to take a sample from the back of your throat and tonsils.

Once the sample has been collected, your doctor will send it off to a lab to be analyzed. The sample will be used to grow colonies of bacteria, which will then be subjected to different antibiotics.

What Does an Antibiotic Sensitivity Test Show?

The results of your antibiotic sensitivity test give your doctor information about how the bacteria causing your infection responds to different antibiotics. It will let them know what treatment is most effective and should be prescribed.

There are three possible results of an antibiotic sensitivity test: 

Susceptible. The antibiotic that was tested was effective in stopping the growth and killing the bacteria that caused your infection.  Your doctor will likely prescribe you an antibiotic since it will be able to eliminate the bacteria easily.

Intermediate. The antibiotic was effective at stopping the bacteria growth at a higher dose.  Your doctor will prescribe an intermediate antibiotic if there are no susceptible ones. You will have to take more of this antibiotic for it to work.

Resistant. The antibiotic was ineffective in eliminating the bacteria that caused the infection in your body. You will need a different antibiotic for your treatment. Your doctor will have to find an antibiotic that is effective to treat your infection. If several antibiotics are found to be resistant, you may have to take a combination of antibiotics.

If you have questions about the results of your antibiotic sensitivity test or antibiotics in general, talk to your doctor. 

WebMD Medical Reference



Centers for Disease Control and Prevention: “2019 AR Threats Report.”, “How Antibiotic Resistance Happens.”

MayoClinic: "Antibiotics: Are you misusing them?"

MedlinePlus: “Antibiotic Resistance.", "Antibiotic Sensitivity Test.” 

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