Antibiotic

An antibiotic is a type of medicine that fights bacteria, either by killing them or by stopping them from growing and multiplying. Antibiotics transformed medicine in the twentieth century, turning once-deadly infections into treatable conditions and making surgery and chemotherapy far safer. Crucially, they work against bacteria but not against viruses, which is why they are useless for colds and flu.

The rise of antibiotic resistance — bacteria evolving the ability to survive the drugs meant to kill them — is now one of the most serious public-health challenges worldwide.

How antibiotics work

Antibiotics exploit differences between bacterial cells and human cells. Common mechanisms include interfering with the bacterial cell wall, disrupting the membrane that surrounds the cell, blocking the machinery that copies DNA or makes proteins, and interrupting essential metabolic pathways. Because human cells lack many of these targets, the drugs can harm bacteria while leaving the patient's own cells largely untouched, though side effects still occur.

Some antibiotics are bactericidal, meaning they kill bacteria directly; others are bacteriostatic, meaning they merely stop growth, letting the immune system clear the infection.

Origins and major classes

The modern era of antibiotics began with the discovery of penicillin in 1928 by Alexander Fleming, who noticed that a mould had killed bacteria in a laboratory dish. Penicillin entered wide medical use in the 1940s and was followed by many other compounds. Some are natural products made by microbes, while others are chemically modified or entirely synthetic.

Major classes include penicillins and cephalosporins, which target the cell wall; macrolides and tetracyclines, which block protein production; aminoglycosides; fluoroquinolones, which interfere with DNA copying; and others. Each class tends to work against particular types of bacteria and carries its own side-effect profile.

Uses and limitations

Doctors prescribe antibiotics for confirmed or suspected bacterial infections such as some pneumonias, urinary tract infections, strep throat, and infected wounds. They are also given before certain surgeries to prevent infection. They do not treat viral illnesses like the common cold, most sore throats, influenza, or viral pneumonia.

Choosing the right drug depends on the likely bacterium, its known resistance patterns, and the patient's circumstances. Broad-spectrum antibiotics act on many kinds of bacteria, while narrow-spectrum ones target fewer types and are often preferred when the culprit is known, to limit collateral damage to helpful microbes.

Antibiotic resistance

Bacteria reproduce quickly and can acquire resistance through random mutation or by exchanging genetic material. When antibiotics are used, susceptible bacteria die while resistant ones survive and multiply. Overuse and misuse — prescribing when unnecessary, using the wrong drug, or stopping treatment early — accelerate this process. The result is infections that are harder or sometimes impossible to treat.

Resistance has serious consequences: longer illnesses, higher medical costs, and greater risk in routine procedures. Hospitals are especially vulnerable because infections can spread among vulnerable patients. Addressing resistance requires multiple strategies at once.

Responsible use

Antibiotics should be taken only when prescribed for a bacterial infection, in the right dose, for the full course as directed. Patients should not save leftover pills or share them. In agriculture, the routine use of antibiotics to promote growth in livestock contributes to resistance and has been restricted in many countries. Better hygiene, infection control, vaccination, and rapid diagnostics all help reduce the need for antibiotics.

Meanwhile, the pipeline of new antibiotics is limited, partly because developing them is scientifically hard and financially unattractive. Encouraging research is an ongoing policy concern.

How resistance spreads

Resistance is a natural consequence of evolution, but human behaviour speeds it up. When a population of bacteria is exposed to an antibiotic, the few that happen to survive pass on their advantage. Resistance genes can also jump between different bacteria through the exchange of small loops of DNA, meaning a harmless bacterium can hand a dangerous trait to a harmful one. Poor sanitation and crowded conditions help resistant strains spread between people, and international travel and trade can carry them across borders quickly.

Some bacteria acquire resistance to several drugs at once, becoming what are sometimes called superbugs. These are especially worrying in hospitals, where patients are already vulnerable.

The search for new drugs

For decades, new antibiotics emerged regularly, but the pace has slowed. Discovering compounds that kill bacteria without harming patients is scientifically difficult, and because new drugs are often reserved for last resort, the financial returns can be limited. Researchers are exploring new sources, such as soil microbes and the deep ocean, as well as alternative approaches like bacteria-killing viruses called bacteriophages and treatments that boost the immune system. Diagnostics that identify the exact bacterium quickly would also help doctors use the right drug and avoid unnecessary prescriptions.

Common misconceptions

Many people believe antibiotics cure any infection, but they do nothing against viruses. Others stop taking them once they feel better, which can leave stronger bacteria behind. Some expect antibiotics to work instantly, although they need time to take effect. And many assume resistance is a problem of the individual taking the drug, when it is really a collective, shared challenge.

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