Your turn
Each lab is one step from the video. Change things and see what happens.
Each lab isolates one part of the story. The models are simplified to show the idea; they are not medical tools.
Tap the buttons and see what happens.
Tap anywhere on the dish to drop in mould. What happens to the bacteria around it?
Add Penicillium anywhere on the plate and watch a clear zone open around it.
Tap the dish to add mould. Where do the germs go?
Pick a part. Which cell has it, the bacterium or your cell?
Compare the wall, the ribosomes and the DNA machinery of the two cells.
Tap a button. Which one has a hard wall?
Add penicillin to the dish. Which cells are left?
Dose a mixed dish with penicillin. Only cells with a wall to break are affected.
Add the medicine. Which ones pop?
The bacteria keep splitting in two. Jam their ribosomes and watch what happens.
Watch the colony double, then block protein synthesis and see the growth stall.
A simplified model: real bacteria divide every few hours, not every few seconds.
Tap each illness to sort it: caused by bacteria, or by a virus?
Sort common infections by cause. Antibiotics only help the bacterial ones.
Tap each card. Can the medicine help?
Not medical advice. Only take antibiotics a doctor prescribes for you, exactly as directed. Some infections can be either kind: a doctor decides.
Give the antibiotic, then let the survivors grow back. Do it a few times. What happens?
Alternate dosing and regrowth, and watch the resistant fraction climb.
Give the medicine, then let them grow. Which ones are left?
A picture of the idea: real resistance takes many generations, and can also spread between bacteria.
Antibiotics are medicines that fight some germs. The germs they fight are called bacteria. Bacteria are tiny living things, much too small to see.
A long time ago, a scientist named Alexander Fleming saw a fuzzy mould in a dish of germs. All around the mould, the germs were gone! The mould made a medicine. He called it penicillin.
A bacterium has a hard wall around it, like a strong net around a balloon. Your body's cells don't have a wall like that.
Penicillin makes weak spots in the wall. Then the bacterium pops. Your cells have no wall, so they stay safe.
A cold is caused by a different germ, called a virus. A virus hides inside your cells, and it has no wall. So antibiotics don't work on viruses.
Sometimes a few germs are a bit tougher. They can live through the medicine and make more tough germs. That's why we only use antibiotics when we really need them.
Note: This page explains how medicines work; it isn't medical advice. If you're ill, talk to a doctor, nurse or pharmacist.
Antibiotics are medicines that fight infections caused by bacteria. They work in one of two ways: they kill the bacteria, or they stop them from growing and multiplying.16
The clever part is how they pick their target. Your body is made of cells too, so a medicine that harmed every cell would harm you. Antibiotics work by attacking things that bacterial cells have but human cells don't.7 Penicillin, for example, stops bacteria from building a cell wall, and your cells don't have a wall at all.
Bacteria are tiny living things, each one a single cell far too small to see without a microscope. They live inside your body, on your skin and all around you. Most are harmless and some are helpful, but some cause infections such as strep throat and urinary tract infections (UTIs).212
Many antibiotics were first found in nature. They are compounds made by bacteria and fungi (such as moulds) to kill or hold back competing microbes.8 Today some are natural products and some are partly or fully made in a lab.12 There are hundreds of different antibiotics, but most fall into six main groups, such as the penicillins and the cephalosporins.10
Bacteria and human cells differ in several ways: many bacteria have a cell wall, and bacteria also use their own kinds of machinery to build proteins and to copy their DNA.7 Each of those differences is a target.
| Target | Example antibiotics | What happens to the bacterium | Why your cells are safe |
|---|---|---|---|
| Cell wall | Penicillins, cephalosporins (beta-lactams) | It can't link new wall pieces together; weak spots form and the pressure inside makes it burst | Human cells have no cell wall |
| Ribosomes (protein builders) | Macrolides such as erythromycin | It can't build proteins, so it can't survive | Human ribosomes have a different shape |
| DNA copying | Quinolones such as ciprofloxacin | Its DNA strands break while being copied and can't be repaired, so it can't live or reproduce | They target the bacterial copying machinery |
| Cell membrane | Polymyxins | Its outer membrane leaks and the cell dies | They bind to the bacterial kind of membrane |
Many bacteria are wrapped in a stiff cell wall, a bit like a strong net around a balloon. The inside of a bacterium is under pressure, and the wall holds it in. As a bacterium grows, it keeps building its wall by linking small molecules together.711
Penicillin and the other beta-lactam antibiotics block that linking step. Without a solid wall to support it, the pressure inside becomes too much and the membrane bursts.7
no wall links → weak spots → burst
Ribosomes are the machines that build proteins, and proteins do almost all of a cell's work. Bacteria and people both have ribosomes, but they are shaped differently. Macrolide antibiotics block only the bacterial kind. A bacterium that can't build proteins can't survive.7
Before a bacterium divides, it copies its DNA. Quinolone antibiotics make the DNA strands break during copying and stop the breaks from being repaired. Without intact DNA, the bacterium can't live or reproduce.711
Some antibiotics kill bacteria outright. Others mainly stop bacteria from growing and multiplying, so your body's natural defences can clear the rest.13 Either way, the number of bacteria causing the infection goes down.
On 3 September 1928, Scottish scientist Alexander Fleming came back from holiday to his lab in London and began sorting through dishes of Staphylococcus bacteria. One dish had a blob of mould growing on it, and the area right around the mould was clear of bacteria.89 The mould was a Penicillium, and Fleming named the bacteria-killing substance it made penicillin.9
Fleming couldn't purify it, though. From 1939, Howard Florey, Ernst Chain and their team at Oxford University turned penicillin into a real medicine, and the first patient was treated in February 1941.8 During the Second World War, US labs worked out how to grow the mould in huge tanks; one of the best strains came from a mouldy cantaloupe melon bought at a market in Peoria, Illinois.8 The mass production of penicillin in the 1940s began the era of antibiotics.811 Fleming, Florey and Chain shared the 1945 Nobel Prize in Physiology or Medicine.9
More discoveries followed: streptomycin in 1943, which worked against tuberculosis where penicillin didn't; the cephalosporins in the 1950s; and the quinolones in the 1960s.11
Colds, flu, most sore throats and most chest colds are caused by viruses, and antibiotics don't work on them.1 Viruses are very different from bacteria (are viruses alive?). A virus has no cell wall and no ribosomes of its own. It can't copy itself alone; it has to get inside your cells and use their parts to make copies.14 That leaves an antibiotic with nothing to attack.
This is why doctors don't prescribe antibiotics for a cold, even if the mucus is thick, yellow or green.1 Antibiotics won't make you feel better if you have a virus, and their side effects can still cause harm.1 Some bacterial infections, such as many sinus infections and some ear infections, also get better without them.1 If you want to know how the body prepares for viruses instead, see how vaccines work.
| Usually caused by bacteria (antibiotics may help) | Caused by viruses (antibiotics don't help) |
|---|---|
| Strep throat | Colds and runny noses |
| Whooping cough | Flu |
| Urinary tract infections (UTIs) | Most sore throats, most chest colds (bronchitis) |
Source for the table: 1
It depends on the antibiotic and on the infection it's treating. Many people start to feel better within a few days.12 Symptoms often ease before the infection is completely gone, so feeling better isn't a sign to stop on your own.12 You may also still be infectious after starting antibiotics: the NHS says it can take anywhere from 48 hours to 14 days to stop being infectious, depending on the infection.10
After the last dose, antibiotics stay in your system for anywhere from a few hours to several days, depending on the medicine, the dose and your age.12
If a doctor decides an antibiotic is the best treatment, the CDC's advice is simple:12
Antibiotics also kill some of the friendly bacteria that normally live in your body and help protect you, which is one reason they can upset your stomach.37
Antibiotic resistance happens when bacteria change so that the drugs designed to kill them no longer work. The bacteria aren't killed and keep growing.3 It's the bacteria that become resistant, not your body.2
Resistance is a naturally occurring process.2 It works like this:34
This is natural selection, the same process behind evolution, happening fast enough to watch. Every time antibiotics are used, they can add to resistance, which is why using them only when they're needed matters.2 The CDC estimates that about 47 million antibiotic courses a year in US doctors' offices and emergency departments are for infections that don't need them, like colds and flu: about 28% of all antibiotics prescribed there.2
Resistant infections can be difficult, and sometimes impossible, to treat.35 In the US, the threats in the CDC's resistance report add up to more than 3 million infections and 48,000 deaths a year.3 Worldwide, about one in six bacterial infections is already resistant to antibiotics, and the World Health Organization counts antimicrobial resistance among the world's top ten global health threats.15 It matters for more than infections: joint replacements, organ transplants and cancer treatment all rely on antibiotics that work.2
The good news is that everyone can help: use antibiotics only when a healthcare professional says you need them, take them exactly as prescribed, and prevent infections in the first place by washing your hands, staying home when you're sick and getting recommended vaccines.12
Curious about the cells themselves? See why cells divide and how bacteria reproduce.
Antibiotics are medicines that kill bacteria or stop them from growing and multiplying. They work by attacking parts that bacterial cells have but human cells don't, such as the cell wall or the bacterial type of ribosome (protein builder). That's how they can harm bacteria while leaving your own cells alone.
Different antibiotics attack different targets. Penicillin and its relatives stop bacteria from building their cell walls, so the pressure inside makes them burst. Macrolides such as erythromycin jam bacterial ribosomes so the bacteria can't make proteins. Quinolones break bacterial DNA while it is being copied. Some antibiotics kill bacteria outright; others stop them multiplying so your immune system can clear them.
It depends on the antibiotic and the infection. Many people start to feel better within a few days. Feeling better doesn't always mean the infection is gone, so keep taking the medicine exactly as your doctor or pharmacist tells you. You may also still be infectious for a while after starting; the NHS says this can be anywhere from 48 hours to 14 days.
Colds and flu are caused by viruses, not bacteria. A virus has no cell wall and no ribosomes of its own: it gets inside your cells and uses their parts to copy itself. So an antibiotic has nothing to hit. Taking antibiotics for a virus won't help you feel better, and their side effects can still cause harm.
Antibiotic resistance is when bacteria change so that an antibiotic no longer kills them. It happens by natural selection: bacteria that happen to carry a helpful change survive, multiply and pass it on. It is the bacteria that become resistant, not your body. The WHO calls antimicrobial resistance one of the world's top ten global health threats.
You usually won't feel the difference straight away. Antibiotics travel through your bloodstream to the infection, and it takes time for the bacteria to be cleared and your symptoms to ease. Many people start to feel better within a few days, depending on the medicine and the infection. Keep taking it exactly as prescribed, even once you feel better.
The CDC advises: take them exactly as prescribed, don't share them with others, don't save them for later, and don't take antibiotics prescribed for someone else. Some antibiotics don't mix well with other medicines or alcohol, so read the leaflet and ask a pharmacist if you're unsure. Tell a healthcare professional about any side effects.