antibiotic
Meaning of antibiotic: Bacteria gain resistance by mutation and by trading genes with one another, which is how a reliable drug stops working.
Definition of antibiotic
An antibiotic is a medicine that kills bacteria or stops them multiplying so that the immune system can finish the job. It has no effect on viruses, so it does nothing for a cold or for influenza. Which one suits a given infection depends on the organism involved, where in the body the infection sits, and local patterns of resistance.
How do antibiotics work?
| Target | How it harms the bacterium | Example class |
|---|---|---|
| Cell wall | The wall cannot be built, so the cell bursts | Penicillins, cephalosporins |
| Protein factory | The bacterium cannot build the proteins it needs | Macrolides, tetracyclines, aminoglycosides |
| DNA handling | The genetic material cannot be copied or untangled | Fluoroquinolones |
| Folate supply | Building blocks for DNA run out | Sulfonamides, trimethoprim |
Each target is something bacteria have and human cells do not, or have in a sufficiently different form. That difference is what makes the drugs tolerable. Some classes kill outright and others merely stop growth, leaving the immune system to clear what remains, which is why the same drug can behave differently in someone whose defenses are weakened.
Why does resistance develop?
Any bacterial population contains rare individuals that survive a given drug, and exposure kills the rest and leaves those survivors the field. Bacteria also pass resistance genes sideways on small rings of DNA, so a gene that arose in one species can turn up in an unrelated one. Every course of treatment applies that pressure, including courses given for illnesses that were never bacterial. The consequence is felt collectively rather than individually: resistant organisms spread between people and through the environment, so the useful lifespan of a drug is a shared resource.
Are all antibiotics used against infection?
No. Several cancer drugs were discovered in soil microbes and are still classed by origin as antibiotics, including the group known as antitumor antibiotics. They damage DNA in dividing cells and are given as chemotherapy, not for infection. The word antibiotic strictly means a substance produced by one organism that inhibits another, while many modern agents are wholly synthetic; in everyday clinical use the word simply means an antibacterial drug.
Also known as
Used in a sentence
The culture result helped guide selection of an antibiotic.
Good to know
Antibiotics have no activity against viruses, and a course that treats no bacterial infection still selects for resistant organisms while carrying the usual risks, including disturbance of the normal gut bacteria.
Word origin
Where “antibiotic” comes from
From anti-, Greek for against, and biotikos, Greek for pertaining to life.