Antibiotic resistance

Antibiotic resistance occurs when bacteria change (or mutate) so antibiotics no longer work to treat infections. Instead of being killed by the antibiotics, some bacteria survive and continue to multiply, causing more harm.

Antibiotic resistance is a growing health problem around the world. The more often antibiotics are used or taken incorrectly, the more chance bacteria have to become resistant to them. Resistant bacteria can also pass their genes to other bacteria, forming a new antibiotic-resistant ‘strain’ of the bacteria. This can make bacterial infections much harder to treat.

Key points

  1. Misuse and overuse of antibiotics has led to many strains of bacteria that cause common infections – such as urinary tract infections, lung infections (pneumonia) and blood infections – now being resistant to commonly used antibiotics.
  2. The failure of these common antibiotics means we have to use other medications, which are often more costly and can have more serious side effects.
  3. There is also the risk that infections which have for many years been easily managed may once again become untreatable and uncontrollable.
  4. Preventing infection and appropriate use of antibiotics are two key ways of fighting antibiotic resistance.

(Video source: World Health Organization Nov 2017)

What causes antibiotic resistance?

The main cause of antibiotic resistance are the misuse and over-use of antibiotics. 

  • Antibiotics are one of the most commonly prescribed medications.
  • Up to 50% of all the antibiotics prescribed for people are not needed or not taken effectively.
  • Antibiotics are also often used in food for animals to prevent, control and treat disease and to promote growth. This can lead to antibiotic resistance in humans because drug-resistant bacteria can remain on meat. When not handled or cooked properly, the bacteria can spread to humans.  

How does antibiotic resistance happen?

Bacteria can become resistant to antibiotics in several ways.

  • Some bacteria can change their outer structure so the antibiotic has no way to attach to the bacteria it is intended to kill.
  • Some bacteria can “neutralise” an antibiotic by changing it in a way that makes it ineffective.
  • Others have mechanisms that pump an antibiotic back outside of the bacteria before it can work.
  • Bacteria can also become resistant through mutation of their genetic material. After being exposed to antibiotics, sometimes bacteria can survive by finding a way to resist the antibiotic. If even one bacterium becomes resistant to an antibiotic, it can then multiply and replace all the bacteria that were killed off.

(Image source: PHARMAC NZ)

The spread of antibiotic resistance occurs when resistant strains of bacteria are passed from person to person and from non-human sources in the environment, including food.

What antibiotic resistance means for you, your family and the community?

If you or someone in your family develop an antibiotic-resistant infection:

  • you may have the infection for longer
  • you may be more likely to have complications from the infection
  • you could remain infectious for longer and pass your infection to other people.

Infections caused by antibiotic-resistant bacteria are harder to treat, usually last longer, often result is longer stays in hospital and are associated with more complications. In serious cases, they can cause death. Doctors have to use to less conventional antibiotics or a combination of different antibiotics to treat these infections. These are usually more costly and can have more-serious side effects.

In New Zealand, the occurrence of antibiotic-resistant bacteria is increasing. Examples include:

  • methicillin-resistant Staphylococcus aureus (MRSA) are a group of bacteria (called Staphylococcus aureus) that are resistant to commonly used penicillin-like antibiotics. 
  • extended spectrum beta-lactamases (ESBL) are chemicals produced by some bacteria that prevent certain antibiotics from working.
  • vancomycin-resistant enterococci (VRE) are a group of bacteria (called enterococci) that are resistant to the antibiotic vancomycin.  

How can antibiotic resistance be prevented?

Key ways you can help stop antibiotic resistance are by avoiding infections and using antibiotics correctly.

Avoiding infection in the first place

Avoiding infections in the first place reduces the amount of antibiotics that have to be used worldwide and this reduces the chance that resistance will develop during treatment. Avoiding infections also prevents the spread of resistant bacteria.

Two simple ways to avoid infections:

  1. Wash your hands. Infections can be avoided by simple measures such as washing your hands or, if that's not possible, using an alcohol hand gel. Wash your hands regularly but especially after visiting the toilet and before preparing food. Many strains of bacteria are spread by person-to-person contact and can survive on surfaces like doorknobs, desktops and benchtops. Read more about hand washing.
  2. Get vaccinated. Vaccination is a way of preventing infectious diseases such as mumps, measles, chickenpox and whooping cough. Vaccination uses your body’s natural defense mechanism – the immune response – to build resistance to specific infections. If you have been vaccinated and you come into contact with that disease, your immune system will respond to prevent you developing the disease. Read more about immunisation.

Using antibiotics correctly

Antibiotics are effective against infections caused by bacteria. They don't work against infections caused by viruses such as the common cold and the flu. Having green or yellow coloured mucous, phlegm or snot isn’t always a sign of a bacterial infection. Read more about snot and sputum.

Symptoms such as cough, sore throat, earache and fever don't always mean that you have a bacterial infection. While some people with these symptoms will need antibiotics, most people won’t because the infection can be caused by viruses and will get better without antibiotics.

4 tips for using antibiotics correctly:

  1.  Use antibiotics only when prescribed by a doctor. 
    Your doctor will assess your condition and will use their clinical judgment, taking into consideration factors such as your symptoms, exposure to infection and test results to prescribe a particular antibiotic if they think it is required. 
  2. Complete your course of antibiotics.
    It is important to complete the course of antibiotics prescribed for you. Even if you are feeling better, take the whole course. By not taking the full course of antibiotics, the antibiotic may wipe out some, but not all, of the bacteria. The surviving bacteria could become more resistant and can spread to other people.
  3. Never share antibiotics with others. 
    This is important because the type of antibiotic may not be targeted to the bacteria causing another infection.
  4. Don't use leftover antibiotics from a previous prescription. 
    The type, dose and amount of antibiotics leftover may not be enough to destroy a new infection – creating more opportunity for resistant bacteria to develop and multiply. 

Learn more

Keep antibiotics working Pharmac, NZ
Antimicrobial resistance
Ministry of Health, NZ
Drug infections are hard to treat (MaoriRoyal Society, Te Aparangi, NZ  
Keeping antibiotics effective, with your help Canterbury District Health Board, NZ
Antibiotics can help, but they cal also harm Canterbury District Health Board, NZ
Your health is very important to us Canterbury District Health Board, NZ 


  1. Antimicrobial resistance – implications for New Zealanders Royal Society, Te Aparangi 
  2. Antibiotic awareness week: a time to reflect on how we prescribe BPAC, NZ 2017
  3. Antibiotic resistance questions and answers Centers for Disease Control and Prevention
Credits: Sandra Ponen, Pharmacist. Reviewed By: Angela Lambie, Pharmacist, Auckland Last reviewed: 15 Nov 2017