Year 9 Science Unit 1 · Disease Lesson 12 of 20 45 min SC5-DIS-12

Antimicrobial Resistance

The era of easy cures is ending. Bacteria are evolving faster than we can develop new drugs. Superbugs like MRSA kill 700,000 people worldwide each year — and without action, that number could rise to 10 million by 2050. Antimicrobial resistance is one of the greatest threats to human health.

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Think First

Before You Begin

Imagine a hospital where doctors notice that a common antibiotic is no longer curing infections it used to treat easily.

Write down your answers before reading on:

  • What do you think might have happened to the bacteria?
  • How could this have been prevented?
  • Why is this problem especially dangerous in hospitals?
Write your thinking in your book before reading on.

Work mode: Digital — answers typed below

Learning Intentions

Know

  • How antimicrobial resistance develops through natural selection
  • What superbugs are and why they are dangerous
  • The causes of antimicrobial resistance

Understand

  • Why overuse of antibiotics accelerates resistance
  • How resistance spreads within and between populations
  • Why developing new antibiotics is difficult

Can Do

  • Explain how natural selection leads to antibiotic resistance
  • Describe ways to reduce antimicrobial resistance
  • Discuss the global threat of superbugs
Key Terms
Antimicrobial resistance (AMR) The ability of microorganisms to survive exposure to drugs designed to kill them.
Superbug A bacterium that has developed resistance to multiple antibiotics, making infections difficult or impossible to treat.
MRSA Methicillin-resistant Staphylococcus aureus — a superbug resistant to many common antibiotics.
Natural selection The process by which organisms with advantageous traits survive and reproduce more successfully than others.
Horizontal gene transfer The transfer of genetic material between organisms that are not parent and offspring, allowing rapid spread of resistance genes.
One Health An approach recognising that human, animal, and environmental health are interconnected.
Core Content
1

How Resistance Evolves

Natural selection in action

Antibiotics

Antibiotics

Antimicrobial resistance is a perfect example of natural selection happening in real time. Here is how it works:

  1. In any bacterial population, random genetic mutations create natural variation. By chance, some bacteria have traits that make them slightly less susceptible to an antibiotic.
  2. When antibiotics are used, susceptible bacteria are killed.
  3. The resistant bacteria survive and multiply, passing their resistance genes to offspring.
  4. With repeated antibiotic exposure, resistant strains become the dominant population.

This process is accelerated when:

  • Antibiotics are overused or misused
  • Patients do not complete their full course
  • Antibiotics are used in agriculture
  • Poor sanitation allows resistant bacteria to spread

Resistance can also spread between bacteria through horizontal gene transfer — bacteria can share resistance genes directly, even between different species. This makes resistance spread much faster than through reproduction alone.

2

Superbugs

When bacteria outsmart our drugs

Superbugs are bacteria that have developed resistance to multiple antibiotics. Some of the most dangerous include:

  • MRSA (methicillin-resistant Staphylococcus aureus): Resistant to penicillin and related antibiotics. Causes skin infections, pneumonia, and bloodstream infections that are difficult to treat.
  • CRE (carbapenem-resistant Enterobacteriaceae): Resistant to carbapenems, antibiotics of last resort. Some CRE are resistant to all available antibiotics.
  • XDR-TB (extensively drug-resistant tuberculosis): Resistant to the most powerful anti-TB drugs. Treatment can take years and has severe side effects.
  • Neisseria gonorrhoeae: The bacterium that causes gonorrhoea is becoming resistant to all available treatments, raising the possibility of untreatable sexually transmitted infections.

Superbugs are especially dangerous in hospitals, where patients have weakened immune systems and invasive procedures create opportunities for infection.

3

The Global Threat

Why AMR affects everyone

The World Health Organization has declared antimicrobial resistance one of the top ten global public health threats. The consequences are staggering:

  • 700,000 deaths worldwide each year are already attributed to resistant infections
  • Without action, this could rise to 10 million deaths annually by 2050 — more than cancer
  • Common medical procedures (surgery, chemotherapy, organ transplants) become much riskier without effective antibiotics to prevent infection
  • The economic cost could reach $100 trillion by 2050

AMR is a global problem because resistant bacteria do not respect borders. International travel, food trade, and medical tourism all spread resistant bacteria worldwide. A superbug emerging in one country can quickly become a global threat.

4

Fighting Back

What Australia and the world are doing

Combating AMR requires action across many fronts:

Stewardship: Using antibiotics only when necessary and choosing the right drug, dose, and duration. Australia's National Antimicrobial Resistance Strategy promotes appropriate prescribing.

Infection prevention: Hand hygiene, sanitation, and vaccination reduce infections, reducing the need for antibiotics. Australian hospitals have strict hand hygiene programs.

Surveillance: Tracking resistance patterns helps guide treatment and detect emerging threats. The Australian Group on Antimicrobial Resistance monitors resistance nationally.

Research: Developing new antibiotics, alternative treatments (phage therapy, monoclonal antibodies), and rapid diagnostic tests. Australian researchers at institutions like the University of Queensland are working on new approaches.

One Health: Recognising that human, animal, and environmental health are linked. Antibiotics used in agriculture can create resistant bacteria that affect humans. Australia regulates agricultural antibiotic use more strictly than many countries.

Common Misconceptions

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"Antibiotic resistance means the person becomes resistant." No — resistance is a property of bacteria, not people. The bacteria infecting a person evolve to survive antibiotics. The person does not change.

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"Superbugs are only a problem in developing countries." No — superbugs are a global problem. MRSA and CRE are significant issues in Australian hospitals. International travel spreads resistant bacteria everywhere.

✗trong>"We can just develop new antibiotics to replace the ones that stop working." Unfortunately not — developing new antibiotics is scientifically difficult and economically unprofitable. No new classes of antibiotics have been discovered since 1987, and pharmaceutical companies have largely abandoned antibiotic research.

Australian Context

MRSA in Australian Hospitals

Healthcare-associated infections: Australian hospitals report thousands of healthcare-associated infections each year, with MRSA among the most concerning. Before strict infection control measures were introduced in the 1990s, MRSA rates in Australian hospitals were rising steadily. Today, hand hygiene compliance programs, patient screening, and isolation protocols have reduced but not eliminated MRSA infections.

Community-acquired MRSA: A new concern is community-acquired MRSA — infections in people with no hospital contact. In remote Indigenous communities, high rates of skin infections combined with antibiotic use have created conditions where resistant strains can emerge and spread. Australian researchers are studying these community strains to inform prevention strategies.

Australian research frontiers: Scientists at the University of Melbourne's Doherty Institute and the University of Queensland are developing new approaches to combat AMR. These include bacteriophage therapy (using viruses that kill bacteria), antimicrobial peptides, and AI-driven drug discovery. Australian researchers also contribute to international collaborations tracking global resistance patterns.

✍ Copy Into Your Books

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How Resistance Evolves

  • Random mutations create variation
  • Antibiotics kill susceptible bacteria
  • Resistant bacteria survive and multiply
  • Resistance spreads through horizontal gene transfer

Superbugs

  • MRSA: resistant to penicillin-related antibiotics
  • CRE: resistant to last-resort antibiotics
  • XDR-TB: resistant to most anti-TB drugs

Fighting AMR

  • Antibiotic stewardship: use only when needed
  • Infection prevention: hand hygiene, vaccination
  • Surveillance: track resistance patterns
  • Research: new treatments and diagnostics
Activities
Activity 1

Natural Selection in Action

Model how resistance evolves.

1 Explain how natural selection leads to antibiotic resistance, step by step. Use the terms variation, selection pressure, survival, and reproduction.
Answer in your book.
2 Why does horizontal gene transfer make resistance spread faster than evolution through reproduction alone?
Answer in your book.
3 A doctor prescribes broad-spectrum antibiotics for a mild infection. Explain why narrow-spectrum antibiotics would be better for reducing resistance.
Answer in your book.
Activity 2

AMR Action Plan

Design strategies to reduce resistance.

1 Write a letter to your local MP explaining why antimicrobial resistance is a threat to Australia and suggesting three policy responses.
Answer in your book.
2 Design a hospital poster promoting hand hygiene as a way to prevent infections and reduce antibiotic use.
Answer in your book.
3 Evaluate the One Health approach to AMR. Why is it important to consider animal and environmental health alongside human health?
Answer in your book.
Multiple Choice
Q

Test Your Understanding

UnderstandBand 4

1. How does natural selection lead to antibiotic resistance?

ABacteria intentionally develop resistance
BRandom mutations create variation; antibiotics select for resistant strains
CAntibiotics cause mutations in bacteria
DHuman immune systems become resistant
RememberBand 3

2. MRSA is dangerous because it:

AIs more virulent than other bacteria
BIs resistant to many common antibiotics
CSpreads faster than other bacteria
DCan only infect hospital patients
UnderstandBand 4

3. Horizontal gene transfer allows bacteria to:

AReproduce faster
BShare resistance genes directly with other bacteria
CDevelop resistance without mutations
DBecome immune to all drugs instantly
RememberBand 3

4. Why is developing new antibiotics difficult?

AScientists do not know how bacteria work
BIt is scientifically challenging and economically unprofitable
CBacteria cannot be grown in laboratories
DAntibiotics are banned in most countries
RememberBand 3

5. The One Health approach to AMR recognises that:

AOnly human health matters
BHuman, animal, and environmental health are interconnected
CAntibiotics should only be used in hospitals
DResistance only occurs in developing countries
Short Answer
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Short Answer Questions

UnderstandBand 4

1. Explain the process of natural selection as it applies to antibiotic resistance. Include the roles of mutation, selection pressure, and reproduction. 4 MARKS

Answer in your book.
UnderstandBand 4

2. Describe three factors that have accelerated the development and spread of antimicrobial resistance. For each, explain how it contributes to the problem. 4 MARKS

Answer in your book.
EvaluateBand 5

3. Without new antibiotics, common medical procedures could become life-threatening. Evaluate this statement, considering the role of antibiotics in modern medicine. 4 MARKS

Answer in your book.

Revisit Your Thinking

Go back to your Think First answer. Has your understanding changed?

Update your thinking in your book.

Answers

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MCQ 1

B — Random mutations create natural variation in bacterial populations. When antibiotics are used, they kill susceptible bacteria but allow resistant mutants to survive and multiply. Over time, resistant strains dominate.

MCQ 2

B — MRSA (methicillin-resistant Staphylococcus aureus) is dangerous because it has developed resistance to many commonly used antibiotics, making infections difficult to treat.

MCQ 3

B — Horizontal gene transfer allows bacteria to share genetic material, including resistance genes, directly with other bacteria — even different species. This dramatically speeds up the spread of resistance.

MCQ 4

B — Developing new antibiotics is scientifically difficult because bacteria have evolved to resist most known mechanisms. It is also economically unprofitable because antibiotics are used for short courses, unlike profitable chronic medications.

MCQ 5

B — The One Health approach recognises that human, animal, and environmental health are interconnected, and that antibiotic use in one area affects resistance in others.

Short Answer 1

Model answer: Antibiotic resistance evolves through natural selection in the following way: (1) Mutation — random genetic mutations occur during bacterial reproduction. By chance, some mutations make bacteria slightly less susceptible to an antibiotic. (2) Selection pressure — when antibiotics are used, they create an environment where susceptible bacteria cannot survive. The antibiotic acts as a selective force. (3) Survival and reproduction — resistant bacteria survive the antibiotic exposure while susceptible bacteria die. The surviving resistant bacteria multiply, passing their resistance genes to offspring. (4) Population change — over repeated antibiotic exposure, resistant bacteria become the dominant population. Eventually, the antibiotic becomes ineffective against most bacteria in that population.

Short Answer 2

Model answer: Three factors accelerating antimicrobial resistance are: (1) Overuse in human medicine: Antibiotics are often prescribed unnecessarily for viral infections or used too broadly when narrow-spectrum alternatives would suffice. This creates constant selection pressure, favouring resistant strains. (2) Use in agriculture: Antibiotics used to promote growth or prevent disease in livestock create reservoirs of resistant bacteria. These bacteria can spread to humans through food, water, or direct contact. (3) Incomplete antibiotic courses: When patients stop taking antibiotics early, the most susceptible bacteria are killed but the strongest survivors remain. These survivors multiply, and their offspring may be resistant. Additionally, international travel spreads resistant bacteria globally, and poor sanitation in some regions allows resistant strains to circulate widely.

Short Answer 3

Model answer: This statement is accurate and concerning. Antibiotics are essential for modern medicine in ways that are often invisible. After surgery, antibiotics prevent wound infections that could otherwise be fatal. Chemotherapy suppresses the immune system, leaving patients vulnerable to infections that antibiotics control. Organ transplants require immunosuppressants, making recipients dependent on antibiotics to survive. Caesarean sections, joint replacements, and dialysis all carry infection risks managed by antibiotics. Without effective antibiotics, the risk of these procedures would increase dramatically, potentially making some too dangerous to perform. This would represent a regression to the pre-antibiotic era when minor injuries and common infections were often fatal. The solution requires not just new antibiotics but also better stewardship, infection prevention, and investment in alternative treatments like phage therapy and vaccines.

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Lesson Game

Resistance Wars

Evolve bacteria to survive antibiotics! Understand how resistance develops and explore strategies to slow its spread in this evolutionary biology game.

Mark lesson as complete

Tick when you have finished all activities and checked your answers.

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