Blood and lab tests
What Are Susceptible Bacteria? Antibiotic Labels Explained
Susceptible bacteria · say it: suh-SEP-tih-bul bak-TEER-ee-uhAlso written: susceptible organisms, susceptible strains, sensitive bacteria, susceptibility
Short answer
Susceptible bacteria are bacteria that a particular antibiotic can kill or stop from growing at usual treatment levels.
What it means
When bacteria are 'susceptible' (sometimes called 'sensitive') to an antibiotic, it means laboratory tests show that the antibiotic should be able to stop them at the doses normally used. If they are 'resistant', the antibiotic is not expected to work well against them. 'Intermediate' falls in between.
Antibiotic labels say they are for infections 'caused by susceptible bacteria' or 'susceptible strains of' named bacteria. This is telling doctors that the medicine only works on bacteria that are not resistant to it. That is why doctors sometimes send a sample, such as urine, for a culture and sensitivity test, to see which antibiotics will work.
Susceptible is the opposite of resistant. It describes the bacteria, not the person; it does not mean you are more likely to catch an infection.
Where you may see it
- The 'Indications' section of antibiotic labels
- Culture and sensitivity lab reports (S, I, R)
- Microbiology results in hospital notes
📄 How it looks on a report
E. coli isolated. Nitrofurantoin: S. Trimethoprim: R.
🙅 What it does not mean
- It does not mean you are susceptible to infection; it is about the bacteria.
- 'Susceptible' to one antibiotic does not mean susceptible to all of them.
- It does not tell you which antibiotic is best for you; your doctor also weighs allergies and other factors.
🎯 Check yourself
Which of these is the right meaning of “Susceptible bacteria”?
🗒️ Questions to ask your doctor
🧾 Reports where you will see “Susceptible bacteria”
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💊 Medicines whose labels mention “Susceptible bacteria”
Plain-English explanations of each medicine, from its official FDA label.
- Amoxicillin
a penicillin-class antibacterial medicine that works against bacteria
- Amoxicillin and Clavulanate Potassium
A penicillin-class antibacterial combined with a beta-lactamase inhibitor, as the label describes it
- Ampicillin Sodium
a penicillin-type antibacterial medicine
- Ceftriaxone
A broad-spectrum cephalosporin antibiotic, as described on the official FDA label
- Cephalexin
a cephalosporin antibacterial medicine (an antibiotic that treats bacterial infections)
- Doxycycline
a tetracycline-class antibacterial medicine (an antibiotic)
- Isoniazid
An antibacterial medicine of the antimycobacterial type, used against tuberculosis bacteria
- Nitrofurantoin
an antibacterial medicine of the nitrofuran type, used for urinary tract infections
- Sulfamethoxazole and Trimethoprim
An antibacterial combination of two medicines: a sulfonamide antimicrobial and a dihydrofolate reductase inhibitor antibacterial.
🔗 Read more from trusted sources
- “Susceptible bacteria” on MedlinePlus ↗
US National Library of Medicine
- MedlinePlus lab test guides ↗
US National Library of Medicine
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General information about a medical word, not advice about your own results. Ask the clinician who ordered the test what it means for you.