Antibiotics – Which To Use?

Antibiotics are an amazing tool, but the growing threat of antibiotic resistance means that vets, and doctors, must use them responsibly.

This means only using them when a bacterial infection has been confirmed, and using the right type of antibiotic to fight the infection.

Finding out if there is an infection, and deciding which drug to use to fight it, can be difficult. The best tools vets have for this are:

  1. Cytology
  2. Culture
  3. Sensitivity
  4. PCR

All tests are most efficient if they are done before antibiotics have been started.

So what are these tests? And why are they important?

Vet tools

Cytology involves looking at cells from a sample under a microscope to see what kind of cells are present and if there are any changes that could indicate disease or other issues.  The cells can be from lots of sample types, but common types include from swabs (including from the ears, nose or of a specific lesion) or from fluid samples such as urine or abscess material.

Cytology can identify the presence of some bacterial infections, but can only aid a preliminary interpretation of the bacterial species.

It can also be used to check for tiny parasites, changes in cell health and number, cell grouping and any other relevantdetails which could indicate problems. 

Culture is when a sample taken from a pet is allowed to grow, commonly in a petri dish. Bacterial and fungal species multiply until their colonies can be seen with the naked eye and identified. This allows the actual species of bacteria or fungi present in a sample to be listed.  

Some viruses can also be cultured but this is more complex and requires a specific viral culture test.

Knowing what bacteria are present allows vets to choose antibiotics that have a higher change of working well.

However, antibiotic resistance is present across the spectrum of available antibiotics, so culture is often combined with a sensitivity test to check the reaction of the specific bacteria to specific antibiotics in the laboratory. 

Sensitivity testing allows the laboratory to suggest specific types of antibiotic that have had a positive effect against the bacteria grown in a culture test in the laboratory. 

Small disks impregnated with different antibiotics are placed on the bacterial cultures to see which antibiotics work best at killing them.

This can help vets choose the most effective antibiotics, which improves response to treatment and reduces the risk of developing antibacterial resistance.

PCR stands for Polymerase Chain Reaction and is a way to multiply DNA – the code inside every living thing. Laboratories can use this to look for specific DNA in a sample to see if specific bacteria, fungi or viruses are present.

This is a very good test to look for a specific disease but is only really useful when that problem is already suspected.