Cracking the Code: How Culture and Sensitivity Tests Help Diagnose Cat Infections

Culture and Sensitivity testing, usually abbreviated as "C&S," is a lab test used to identify the presence and type of bacteria causing an infection and to determine which antibiotics are likely to be effective in killing the bacteria. Samples for a culture can be taken from a cat's urine, blood, body fluids, pus, secretions, or tissues. The sensitivity test is a follow-up to the culture analysis. Once bacteria are cultured and isolated on a medium, they are tested against different antibiotics to find out which ones are effective.

What Does Culture and Sensitivity Testing Reveal for Cats?

A normal culture result shows "no bacterial growth," unless the sample is taken from areas where bacteria are typically present, like the nose or mouth. A positive result indicates that a microorganism or bacteria was found. In most cases, the specific bacteria can be identified (e.g., Streptococcus species). Sensitivity testing follows a positive culture result.

Sensitivity testing reveals which antibiotics (or antimicrobial drugs) are most effective against the isolated bacteria, which are moderately effective, and which are likely to be ineffective for treating the infection.

 

How Is Culture and Sensitivity Testing Performed?

Culture typically involves a special swab applicator. The applicator is placed in the fluid, tissue, or organ to be tested, with the tip being moistened and placed in a special transport container for analysis. This is then sent to the lab for further analysis and sensitivity testing. If not using "culture tubes," collected fluid samples are usually transferred from a sterile syringe into a sterile container. Blood cultures use special broth mediums for testing. Different techniques and mediums are used to culture anaerobic bacteria (those that live without oxygen) or fungi (mold).

The collected sample material is then spread on a culture plate and placed in an incubator. The culture plate is checked periodically for bacterial growth. Once growth is observed, specific biochemical tests and microscopic examination are used to identify the exact type of bacteria.

After the bacteria are identified, they are transferred to another culture plate and subjected to various antibiotics. The effectiveness of these antibiotics is then evaluated by observing how they inhibit bacterial growth.

Some veterinary clinics can culture and identify bacteria in-house, but most veterinarians send samples to a veterinary reference lab. Results typically take about five days, except for fungal cultures, which can take weeks. Preliminary results may be available in two days.

 

Is Culture and Sensitivity Testing Painful for Cats?

Collecting a culture isn't painful, but accessing the infected area to obtain a sample might cause some discomfort depending on its location. If a needle is used to draw fluid from a cyst or body cavity, there might be some pain at the needle's entry point. However, most cultures come from secretions or urine with little to no pain involved.

 

Is Sedation or Anesthesia Needed?

Collecting cultures from secretions generally doesn't require sedation or anesthesia. If the culture is obtained during surgery, anesthesia will be necessary.