D135
Culture and Sensitivity,
Serology, and Virus Isolation

Bacteria Culture and Sensitivity: When a bacterial infectious agent is suspected, it is recommended that a culture and sensitivity be performed. Problems such as calf scours, adult diarrhea, abortions, mastitis, pneumonia, and severe abscess outbreaks are reasons to use a culture and sensitivity to look for a possible bacterial cause. Samples used for culture and sensitivity include the following:

  1. Manure from an animal with diarrhea. A small manure sample should be taken from the animal. Avoid contaminating the sample with manure from other animals.
  2. A sample taken from the nasal passages, lungs, wound, or abscess.
  3. Tissue and organ samples taken from a recently euthanized or deceased animal. The entire aborted fetus and placenta are often helpful.
  4. Milk from a quarter suspected of having mastitis.
  5. Bulk tank milk samples.

(The taking and handling these types of samples may require special training and a veterinarian’s assistance.)

To perform a culture, take one of the above samples and send it to the appropriate laboratory as quickly as possible. At the lab, the sample is placed on a culture medium and allowed to grow. Identifying the bacteria is based on the growth characteristics of the bacteria on the particular medium, microscopic examination, and other procedures. Once the type of bacteria is determined, it is subjected to several different antibiotics. Sensitivity is determined by how the bacteria responds to the antibiotics. Sensitivities are reported as Resistant, Sensitive, and Intermediate. Resistant means the particular antibiotic is not effective against that bacteria. Sensitive means the particular antibiotic is effective against that bacteria, and Intermediate means the antibiotic is moderately effective against that bacteria. The appropriate treatment for the problem can then be initiated without trying to guess which antibiotic may or may not work.

Serology and Virus Isolation: When a viral cause of disease is suspected, it is recommended that the virus be identified. Problems such as pneumonia, abortions, and calf scours are reasons to identify the possible viral cause.

  1. Samples used for virus identification include the following:
  1. Blood samples for serology (these samples show if an animal has been exposed to a virus and often require a second blood sample to be taken 14-21 days after the first).
  2. Manure from an animal with diarrhea (especially calf scours).
  3. A sample taken from the nasal passages or the lungs.
  4. Tissue and organs from a recently euthanized or deceased animal. The entire aborted fetus and placenta are often helpful.
  5. Bulk tank milk samples.

(Contact a veterinarian for specifics on handling these samples.)

  1. Once these samples are properly taken and transported to the appropriate lab, many tests can be performed. Following are some of these tests:
  1. Virus isolation - This is where the laboratory finds and identifies the virus. This test can be expensive, but is very specific for identifying the virus.
  2. IFA or indirect fluorescent antibody - This test is used to identify the virus. This test is often performed for respiratory problems.
  3. Serologic tests - These tests are performed on blood samples and are used to determine immune responses to specific viruses. These immune system responses are identified as titers and can sometimes appear as a response to vaccination. As a consequence, a second blood sample is often taken and tested to help determine if there is a natural infection or a response to vaccination.
  4. ELISA or enzyme linked immunosorbent assay - This is also a blood test to identify the specific antibodies produced by the immune system against a virus.

Once a virus has been identified as the problem, appropriate measures, such as herd vaccination and/or culling of affected animals, can be initiated.