ABSTRACT: Antibiotics are essential medicines in the veterinary practice to help preserve the health and welfare of our animals. However, antibiotic resistance is an important topic of discussion for both the medical and veterinary professions. It is something we clearly all need to take seriously – and veterinary nurses need to be aware of the facts, to help them guide clients on responsible antibiotic use, once the vet has prescribed antibiotics for the treatment of a condition You might need to explain why an antibiotic has not been prescribed, for example, or to impress upon a client the importance of finishing the prescribed course.

What are antibiotics?   

Antibiotics are chemicals that inactivate or damage bacteria. Most are naturally produced by bacteria and fungi; others are man-made but have the same effect. The term antibiotic is used universally to describe this whole range of chemicals. Strictly, it should only apply to the naturally derived chemical substances; but we will use the popular terminology here.

Antibiotics are administered to animals – as with people – to kill or inhibit bacteria that are causing infections. Antibiotics are not effective against viruses at all.

What is resistance?

Antibiotic resistance is the ability of a microorganism to withstand the effects of an antibiotic. It is recognised that there is an inherent risk of antibiotic resistance developing with the use of any antibiotic in any species.

It is widely agreed that resistant strains of bacteria found in animals have largely resulted from the use of antimicrobials in veterinary medicine; and that resistant strains of bacteria found in humans have resulted from the use of antimicrobials in human medicine

Resistance is the ability of an organism to survive in the presence of concentrations of a chemical which are normally lethal to organisms of that species. When bacteria are exposed to an antibiotic, various things can happen:

• they can be killed

• they can be weakened or disabled thus making them easier for the animal’s own natural defences to kill them

   they can remain unaffected or resistant.

What actually happens depends largely on whether the antibiotic is from the correct antibiotic class to work against the particular bacteria, and whether the antibiotic is present in a sufficiently high concentration. Not all antibiotics will work against all bacteria and some bacteria require higher concentrations of antibiotic to kill them.

Interestingly, resistance is a natural phenomenon and was present in bacteria before antibiotics were used. There are several classes of antibiotics, and within each class there are various antibiotics, each slightly different. It is important, therefore, to remember that if an alternative antibiotic is used from a range to which a type of bacterium is sensitive, then the bacteria will still be killed.

Just because a bacterium is resistant to one class of antibiotic does not mean that it is resistant to all classes of antibiotic. However, some bacteria can be resistant to more than one antibiotic class and these are called multi-resistant. It is these bacteria that cause the most concern.

How does antibiotic resistance come about?

This is a natural phenomenon and has been around for as long as bacteria themselves. Bacteria, isolated from a glacier formed long before the discovery and use of antibiotics, have been found to be resistant to some antibiotics. A certain level of inherent bacterial resistance to antibiotics must, therefore, be expected; but surviving bacteria will be those that are resistant.

It is difficult to predict how quickly resistance will develop as it depends – amongst other things – on the class of antibiotic, the type of bacteria, the level of exposure those bacteria have to the antibiotic, and the ability of the resistant bacteria to survive and replicate.

After resistance has developed in particular bacteria, it may in time disappear or the resistant strains may be replaced by susceptible bacteria. There is still much that is unknown about what happens to antibiotic resistance after it has developed. It is the subject of much ongoing research.

What are the effects of antibiotic resistance?

When resistant bacteria cause infections, the choice of antibiotic that can be used to treat that infection is reduced. If immediately recognised, the doctor or vet can use an alternative antibiotic with little or no risk to the patient.

If not recognised until the initial course of antibiotics fails to work, the delay between initial diagnosis and the start of successful treatment can result in unnecessary suffering and a deterioration of the patient's condition.

What can be done to help minimise antibiotic resistance?

By working with their farmer clients on the development of appropriate herd/flock health plans, farm animal vets can work to reduce the need to treat bacterial infections in animals. In this way, administration of antimicrobials to farm animals should be complementary to good farm-management practice and properly designed vaccination programmes to help prevent infectious disease.

Many disease conditions can be avoided or minimised by using management practices that significantly reduce exposure to disease-causing bacteria and by optimising the environment for the animal, including good hygiene and biosecurity, nutrition and vaccination programmes. However, even where these preventive steps are taken, there will still be occasions when animals will need to be treated with antibiotics.

It is important to use antibiotics at the correct dose rate. This has been calculated, independently assessed by regulatory bodies and authorised as being sufficient to ensure that the appropriate quantity of the antibiotic reaches the site of infection for a sufficient amount of time to ensure the bacteria are killed, such that the animal recovers from the infectious disease.

If the correct dose is not given, or if the course is not completed, some bacteria may survive and these may be the ones that are less susceptible to treatment. They may reproduce and hence the numbers of these less-susceptible bacteria may increase within the population as a whole.

Remember, antibiotics treat bacterial infections: they do not treat viral infections. So if animals with suspected viral infections are examined and treated by a veterinary surgeon, owners should not always expect an antibiotic to be prescribed.

If antibiotics are prescribed, it is essential that owners are aware of the importance of completing the course at the prescribed dose rate, even if the animal appears in the owners eyes to no longer to need the medication. This is something that a veterinary nurse might well need to explain, in order to back up the advice a client will have received from the vet in the consulting room.


Antibiotics will remain essential tools to treat infectious diseases in both farm animal and companion animal practice. It is essential that animal owners administer these products as specified by the prescribing veterinary surgeon.

Farm visits to treat sick animals or visiting the surgery with a pet can be a stressful time – for owners as well as animals. Some can forget what they have been told before they even leave the practice!

Armed with the facts, you can help the owner understand their animal’s treatment regimen. For extra back up, don’t forget that NOAH’s Pet Health Information website, www.pethealthinfo.org.uk contains unbranded advice that many practices
choose to recommend to owners, to reinforce the advice they have been given.

Advice on responsible use of medicines for farm animals can be accessed via the Responsible Use of Medicines Alliance (RUMA) website, www.ruma.org.uk. By using antibiotics responsibly, we can ensure that these products will remain available for veterinary use in the future. 


Donal Murphy MVB MRCVS

Donal Murphy qualified from University College Dublin in June 1999. Since then he has been based in the UK where he has worked in both mixed and small animal practice. In January 2010, Donal commenced employment with the National Office of Animal Health (NOAH), the organisation that represents the UK animal medicines industry. He also continues to work as a locum in small animal practice on a regular basis.

To cite this article use either

DOI: 10.1111/j.2045-0648.2012.00236.x or Veterinary Nursing Journal Vol 27 pp 422-423

Veterinary Nursing Journal • VOL 27 • November 2012