Culture and Sensitivity (C & S) in Dogs

Culture and sensitivity, commonly abbreviated as “C&S”, is a laboratory test used to determine the presence and type of bacteria in an infection and determine the antibiotics most likely to be effective in killing the bacteria in the dog or other animal. The sample submitted for culture can be urine, blood, body fluids, pus, discharge or tissue. The “sensitivity” test follows the culture. Once the bacteria have been grown and isolated in a culture medium, they are tested against different antibiotics to determine which drug(s) is likely to be effective. There is no real contraindication to performing this test in dogs.

What Does a Culture and Sensitivity Test Reveal in Dogs?

Normal culture results yield “no bacterial growth” unless the sample is taken from an area usually inhabited by bacteria such as the nose or oral cavity. Positive results mean that a microorganism or bacterium was found. In most cases, the specific bacteria are identified (for example, streptococcus spp.). A positive culture is needed before a sensitivity test can be done.

Sensitivity reveals which antibiotics (or antimicrobial drugs) would be most effective against the isolated bacteria, which antibiotics are moderately effective, and which antibiotics would likely have no effect on the infection.

How Is a Culture and Sensitivity Test Done in Dogs?

Cultures are commonly taken using a special cotton-tipped applicator. This applicator is placed in the fluid, tissue or organ to be tested, and the tip is soaked and placed into a commercially prepared transport container, which is then submitted to a laboratory. When these “culturettes” are not used, it is typical for a sample of collected fluid to be transferred from a sterile syringe into a sterile container. This is then submitted for culture and sensitivity. Blood cultures are done with special broth media. Different techniques and media are used for culturing anaerobic bacteria (those that live without oxygen) or fungi (molds).

A sample of the collected material is then spread out over the culture medium plate (called a Petri dish) and placed in an incubator. At periodic intervals the plate is checked for bacterial growth. Once bacterial growth has been established, the exact type(s) is determined based on specialized biochemical tests and appearance under the microscope.

When the bacterial organism has been identified, it is then transferred to another plate and subjected to various antibiotics. The culture medium is then examined for inhibition of bacterial growth.

Some veterinary hospitals are able to incubate and identify bacterial cultures in their clinic but most veterinarians submit the samples to a veterinary reference laboratory. Results are usually completed in approximately 5 days, except for fungal cultures which may take weeks. Preliminary results may be available after 2 days.

Is a Culture and Sensitivity Test Painful to Dogs?

Obtaining a culture is not painful but getting to the site of the infection may involve some discomfort depending on the location of the lesion. If the sample is obtained by inserting a needle into a fluid filled mass or body cavity, there will be some pain associated with the needle stick. Most often, cultures are taken of discharges or urine and involve little or no pain.

Is Sedation or Anesthesia Needed for a Culture and Sensitivity Test?

Neither sedation nor anesthesia is needed in obtaining cultures from discharges. If the culture is taken during a surgical procedure, anesthesia for the procedure will be required.