Preventing Antibiotic Resistance Revision Notes | GCSE Edexcel Higher Biology

1. The Growing Crisis

Imagine going to hospital for routine surgery, only to catch an infection that no antibiotic can cure. This nightmare scenario is becoming reality as bacteria evolve resistance faster than we can develop new drugs.

Antibiotic resistance happens through natural selection. When antibiotics are used, most bacteria die - but a few with random mutations survive. These resistant bacteria multiply rapidly, creating whole populations that laugh in the face of our best medicines.

The scary part? We're accidentally speeding up this process through our own actions. Every time we misuse antibiotics, we're training bacteria to become stronger.

2. How Natural Selection Creates Superbugs

Picture a population of bacteria in your throat during a strep infection. Most are vulnerable to penicillin, but one in a million has a random mutation that makes it resistant.

When you take antibiotics, here's what happens: the vulnerable bacteria die within hours. But that one resistant bacterium? It survives and starts dividing every 20 minutes. Within days, your infection is dominated by resistant bacteria.

This is natural selection in fast-forward. The antibiotic acts as the selection pressure - it doesn't create resistance, but it gives resistant bacteria a massive survival advantage.

3. Doctor Responsibility - Prescribing Appropriately

Doctors hold the first line of defence against resistance. They must resist pressure from patients who demand antibiotics for every sniffle and cough.

Here's the crucial rule: antibiotics only work against bacteria, never viruses. Yet studies show that 30% of antibiotic prescriptions are unnecessary - often for viral infections like colds and flu.

When doctors prescribe antibiotics for viral infections, they're exposing harmless bacteria in your body to selection pressure for no medical benefit. These bacteria can develop resistance and later cause serious infections.

Smart prescribing means using diagnostic tests to confirm bacterial infections before prescribing. It also means choosing narrow-spectrum antibiotics that target specific bacteria rather than broad-spectrum ones that kill everything.

4. Patient Responsibility - Completing the Course

You start taking antibiotics and feel better after two days. Surely you can stop now and save the rest for next time? This thinking is dangerous and creates resistant bacteria.

Here's why completing the course matters: antibiotics kill the weakest bacteria first. The stronger, more resistant bacteria take longer to die. If you stop early, you've eliminated the competition but left the toughest bacteria alive.

Worked example: What Happens When You Stop Antibiotics Early

A patient has 1 million bacteria causing infection. 999,000 are sensitive to antibiotics, 1,000 are partially resistant. They take antibiotics for 3 days instead of the prescribed 7 days.

1. 999,000 sensitive bacteria killed 1,000 resistant bacteria survive — Antibiotics kill the easiest targets first
2. 1,000 resistant bacteria remain alive No competition from sensitive bacteria — Patient thinks they're cured but resistant bacteria survive
3. 1,000 → 2,000 → 4,000 → 8,000 resistant bacteria — Bacteria double every few hours without antibiotic pressure
4. Patient now has infection of 100% resistant bacteria — Next infection will be much harder to treat

Answer: Stopping early selects for resistant bacteria and makes future infections untreatable

The prescribed course length is calculated to kill even the most resistant bacteria in the population. Stopping early is like leaving the strongest enemy soldiers alive after a battle.

5. Agricultural Use - The Hidden Problem

Here's a shocking statistic: 80% of antibiotics aren't used in hospitals - they're fed to farm animals. This massive agricultural use creates a perfect breeding ground for resistant bacteria.

Farmers add antibiotics to animal feed not to treat disease, but to promote growth and prevent infections in crowded conditions. This means healthy animals are constantly exposed to low doses of antibiotics.

Low-dose, long-term antibiotic exposure is the perfect recipe for resistance. It's not enough to kill bacteria quickly, but it's enough to create selection pressure. Resistant bacteria develop in animal guts, then spread through meat, milk, and farm runoff.

Some countries have banned growth-promoting antibiotics in farming, leading to reduced resistance rates. However, global food trade means resistant bacteria can spread worldwide regardless of local policies.

6. The Development Crisis - Why New Drugs Can't Keep Up

You might think the solution is simple: just develop new antibiotics faster than bacteria develop resistance. Unfortunately, this is a race we're losing badly.

Developing a new antibiotic takes 10-15 years and costs over £1 billion. Meanwhile, bacteria can develop resistance to a new antibiotic within months of its first use. It's like trying to build a dam while the flood is already here.

The economics make it worse. Pharmaceutical companies make more profit from drugs people take daily for years (like blood pressure medication) than from antibiotics people take for just a week. Many companies have abandoned antibiotic research entirely.

Even when new antibiotics are developed, they're often held in reserve for the most serious infections. This 'last resort' strategy helps preserve their effectiveness but means there's little market incentive to develop them.

7. Exam Technique - Tackling Resistance Questions

Antibiotic resistance questions often test your understanding of natural selection and evolution. Examiners love to ask about the mechanisms behind resistance development.

Common exam mistakes include saying antibiotics cause mutations (they don't - mutations are random) or that bacteria become resistant on purpose (evolution has no goal). Remember: variation exists first, then selection acts on it.

For evaluation questions about preventing resistance, always consider multiple stakeholders: doctors (appropriate prescribing), patients (completing courses), farmers (reducing agricultural use), and governments (funding new research and regulation).