Before antibiotics, a simple scratch could kill. Pneumonia, tuberculosis, and infected wounds were death sentences. The discovery of penicillin in 1928 transformed medicine — but these miracle drugs only work if we use them wisely.
Think about the last time you or someone you knew was prescribed antibiotics by a doctor.
Write down your answers before reading on:
Targeting bacterial weaknesses
Antibiotics exploit the differences between bacterial cells and human cells to kill or inhibit bacteria without harming the patient.
Common mechanisms include:
Broad-spectrum antibiotics work against many types of bacteria. Narrow-spectrum antibiotics target specific bacteria. Using narrow-spectrum antibiotics when possible reduces harm to beneficial gut bacteria.
Fighting viruses inside cells
Antiviral drugs are much harder to develop than antibiotics because viruses use the host cell's own machinery to replicate. Drugs must target viral processes without harming human cells.
Antiviral strategies include:
Unlike antibiotics, which can cure bacterial infections, antivirals usually reduce symptoms and duration rather than eliminating the virus completely. Many viral infections are best prevented by vaccines.
Why following instructions matters
Using antibiotics and antivirals correctly is essential for both individual health and public health:
Complete the full course: Even if you feel better after a few days, stopping antibiotics early allows surviving bacteria to multiply. These survivors may be more resistant to the antibiotic.
Do not share medications: The antibiotic prescribed for one person may not be appropriate for another. Different bacteria require different antibiotics.
Do not use leftover antibiotics: Old antibiotics may have lost effectiveness, and using the wrong antibiotic contributes to resistance.
Do not demand antibiotics for viral infections: Colds, flu, and most sore throats are caused by viruses. Antibiotics will not help and contribute to resistance.
Take antivirals early: Antivirals for influenza work best within 48 hours of symptom onset. Delayed treatment is less effective.
Fighting fungi and parasites
While antibiotics and antivirals are the most commonly discussed antimicrobial drugs, other types are also important:
Antifungals treat fungal infections by:
Antiparasitics treat infections caused by protists and worms:
Like antibiotics, these drugs must be used responsibly to prevent resistance from developing.
"Antibiotics can cure any infection." No — antibiotics only work against bacteria. They are ineffective against viruses, fungi, and parasites. Using antibiotics for viral infections is ineffective and contributes to antimicrobial resistance.
"It is okay to stop taking antibiotics once you feel better." No — stopping early allows the strongest bacteria to survive and multiply. These survivors may be resistant to the antibiotic, making future infections harder to treat.
National Antimicrobial Resistance Strategy: Australia has a national strategy to combat antimicrobial resistance, coordinated by the Australian Commission on Safety and Quality in Health Care. The strategy promotes appropriate prescribing, surveillance of resistance patterns, and research into new treatments.
Antibiotic use in agriculture: Australia has relatively low use of antibiotics in livestock compared to many countries. The Australian Pesticides and Veterinary Medicines Authority regulates agricultural antibiotic use. However, imported meat from countries with high agricultural antibiotic use can contribute to resistant bacteria entering Australia.
Community antibiotic use: Australians are among the highest users of antibiotics in the developed world. Many prescriptions are for respiratory infections that are likely viral. The NPS MedicineWise program works to reduce unnecessary antibiotic prescribing through education for doctors and patients.
1. Antibiotics work by:
2. Why are antiviral drugs harder to develop than antibiotics?
3. Which statement about antibiotic use is correct?
4. A bactericidal antibiotic:
5. Antiviral drugs for influenza work best when taken:
1. Explain why antibiotics can cure bacterial infections but cannot treat viral infections. Use specific examples of how antibiotics target bacteria. 4 MARKS
2. Describe the risks of misusing antibiotics (not completing courses, using leftovers, taking them for viral infections). Explain how each contributes to antimicrobial resistance. 4 MARKS
3. Compare the mechanisms of action of antibiotics and antiviral drugs. Evaluate which is more challenging to develop and why. 4 MARKS
Go back to your Think First answer. Has your understanding changed?
B — Antibiotics target features unique to bacteria, such as cell walls, bacterial ribosomes, and bacterial metabolic pathways, which human cells do not have.
B — Viruses use the host cell's own machinery to replicate, so antiviral drugs must interfere with viral processes without harming human cells. This makes targeted treatment much more difficult.
C — Antibiotics only work against bacteria. Using them for viral infections is ineffective and contributes to antimicrobial resistance.
B — Bactericidal antibiotics kill bacteria directly (e.g., penicillin). Bacteriostatic antibiotics stop bacteria from multiplying.
B — Antivirals for influenza (like oseltamivir/Tamiflu) work best when taken within 48 hours of symptom onset, as they prevent new virus particles from spreading.
Model answer: Antibiotics can cure bacterial infections because they target structures and processes that bacteria have but human cells lack. For example, penicillin inhibits bacterial cell wall synthesis — bacteria without strong cell walls burst and die, while human cells (which have no cell walls) are unaffected. Other antibiotics target bacterial ribosomes or bacterial DNA replication enzymes, which differ from human versions. Viruses, however, are not cells. They have no cell walls, ribosomes, or metabolic pathways of their own. They replicate inside host cells using the cell's machinery. Because viruses do not have the bacterial targets that antibiotics attack, antibiotics are completely ineffective against viral infections like colds, flu, and COVID-19.
Model answer: Misusing antibiotics in three ways contributes to antimicrobial resistance: (1) Not completing courses: When antibiotics are stopped early, the most susceptible bacteria are killed, but the strongest survivors remain. These survivors multiply, and their offspring may be resistant. (2) Using leftovers: Leftover antibiotics may not be the right type for the current infection. Using the wrong antibiotic applies selective pressure without killing the pathogen, allowing resistant bacteria to thrive. (3) Taking antibiotics for viral infections: Antibiotics have no effect on viruses, but they do affect the bacteria living in and on the body. This disrupts beneficial bacteria and creates opportunities for resistant strains to multiply and spread. Each misuse accelerates the evolution of antibiotic-resistant bacteria, making future infections harder to treat.
Model answer: Antibiotics work by targeting specific features of bacterial cells that human cells lack, such as cell walls (penicillin), bacterial ribosomes (tetracycline), or bacterial DNA replication enzymes (fluoroquinolones). Because bacteria are cells with their own machinery, there are multiple distinct targets to attack. Antiviral drugs must interfere with viral processes without harming host cells. This is more challenging because viruses use the host cell's own machinery to replicate. Antivirals typically work by blocking viral entry, inhibiting viral enzymes (like reverse transcriptase or neuraminidase), or preventing viral release. Developing antivirals is more difficult because: there are fewer viral-specific targets; the targets often resemble human cellular processes; and achieving effective concentrations inside cells without toxicity is challenging. Consequently, fewer antiviral drugs exist compared to antibiotics, and most reduce rather than cure viral infections.
Prescribe the right treatments! Match infections to antibiotics, antivirals, or other therapies in this medical decision-making challenge.
Tick when you have finished all activities and checked your answers.