CELLS, TISSUE AND INFECTION
Culture and Sensitivity Testing
Laboratory testing that helps identify certain bacteria and determine which antimicrobial medications may be effective.
THE SHORT VERSION
Testing helps answer a clinical question.
A culture allows selected organisms to grow from an appropriately collected sample. Susceptibility testing then assesses which antimicrobial agents are more or less likely to work against the identified organism.
What is this test?
A culture allows selected organisms to grow from an appropriately collected sample. Susceptibility testing then assesses which antimicrobial agents are more or less likely to work against the identified organism.
A culture attempts to grow organisms from a sample, and susceptibility testing evaluates selected medicines against an identified isolate. A representative sample and the history of previous antibiotics matter. The laboratory result must be interpreted with the site of infection and the animal's condition; a drug that tests favorably is not automatically the safest or most practical choice. Some organisms require special methods, and a negative routine culture does not exclude every infection. Ask what the sample is intended to identify and whether treatment should begin while results are pending.
What information can it provide?
- The sample source may include urine, a wound, an ear or another location chosen by the veterinarian.
- Sterile or carefully collected samples are important because contamination can complicate interpretation.
- Susceptibility results guide antibiotic selection together with tissue location, safety and the animal’s history.
- Some organisms require specialized culture conditions or additional testing.
Antibiotic selection depends on the suspected or confirmed bacteria, the site of infection, and the animal's safety needs. A culture identifies organisms that grow from a sample; susceptibility testing helps assess which medicines may work against them. The laboratory result is considered alongside tissue penetration, dosing feasibility, and the clinical response. Antibiotics do not treat viruses, and adding one without a clear reason can obscure the investigation or cause adverse effects. Follow the current prescription rather than using leftovers from a previous illness.
An infectious illness depends on both the organism and the animal's ability to resist it. Exposure does not always produce the same severity of illness in every animal. Age, previous immunity, nutrition, stress, and concurrent disease can influence the outcome. The infection may also cause complications that need treatment separately from the organism itself. For example, correcting fluid loss or supporting breathing can be essential even when a targeted medicine has already been started.
When might your veterinarian recommend it?
- Investigate a persistent, recurrent or complicated suspected bacterial infection.
- Support antimicrobial stewardship rather than repeatedly guessing at an antibiotic.
- Clarify whether a urinary or wound sample contains a clinically meaningful organism.
What can owners do before the visit?
- Tell the clinic about current or recent antibiotics before sampling.
- In some cases, collecting a sample before starting antibiotics improves interpretability when the animal’s condition allows.
- Never stop a prescribed antibiotic without explicit veterinary direction.
A useful specimen depends on the test, collection method, freshness, storage, and contamination. Ask the clinic what is needed before collecting urine, stool, water, tissue, or other material. Mark the collection time and relevant history, and follow transport instructions. A convenient home sample may answer one question while a differently collected sample is needed for another. Do not postpone care for an unstable animal while trying to obtain a perfect specimen; the team can arrange an appropriate collection when safe.
What can this test not tell you by itself?
- Culture results may require time, and an unstable animal may need immediate treatment before a result is available.
- Contaminated samples can grow organisms that are not causing disease.
- A susceptible laboratory result must still be evaluated against drug safety, location and species.
Microscopy allows the team to examine details too small to see during the physical examination. Cytology evaluates individual cells and material collected from a site, while other microscopic tests look for specific organisms or structures. The value of the result depends on obtaining a representative sample. A result that does not identify the cause is not necessarily proof that the site is healthy; deeper, repeat, or different sampling may be appropriate if the clinical concern remains.
Disease prevention includes the route by which animals, people, equipment, bedding, feed, or water can carry a problem between groups. Separation works best when it also includes dedicated tools, careful handling order, and an appropriate cleaning plan. A newly arrived animal may appear well while a disease is incubating. Ask which tests or observation period suit the species and suspected disease before mixing groups. Cleaning, disinfection, and disposal requirements differ between organisms, so a single household product is not a universal solution.
Do not change medication, interpret an abnormal number as a diagnosis or delay urgent treatment without direction from your veterinary team.
Useful questions for your appointment
- Is this the right sample and collection method for the problem?
- Could recent antibiotics change the result?
- How will the veterinarian select the safest effective medication and plan follow-up?