Isolation of M. paratuberculosis is considered the most definitive method for
diagnosis of the infection. However, culture is also the most difficult and slowest method
for diagnosis. Conventional methods for isolation of M. paratuberculosis use
bacteriological media in test tubes, much as for other bacteria, and typically take 16
weeks. Many laboratories perform conventional culture for M. paratuberculosis.
Contact your state veterinary diagnostic laboratory for information.
At the Johne's Testing Center, radiometric culture for M. paratuberculosis is
used. The radiometric culture technique is an adaptation of the BACTEC system. The BACTEC
system is the most widely used method for isolation of mycobacteria from human specimens.
By modifying the culture medium of the BACTEC system, this radioisotope-based
mycobacterial detection method was demonstrated to detect M. paratuberculosis
faster and with greater sensitivity than conventional culture methods.
Feces or tissue samples from any animal species can be cultured. Fecal samples, at least 3 grams (a thumb-size lump), should be placed in sterile, sealable, plastic bags such as Whirlpacks, or a wide-mouth, leak-proof container. Inverted OB sleeves are not accepted. The best tissue samples for isolation of M. paratuberculosis are the ileocecal junction, ileum, and lymph nodes adjacent to these parts of the intestine. Tissue samples should be collected promptly from animals being necropsied and immediately refrigerated.
Overnight or second day UPS/FedEx delivery on cold packs is recommended.
The samples should be shipped to arrive Monday - Friday, 8 am to 4 pm. Overnight mail is
also acceptable. Results of cultures done on fresh samples, promptly delivered to the
laboratory, are most meaningful. If absolutely necessary however, frozen samples can be
tested. The shipping address is: Johne's Testing Center
School of Veterinary Medicine, Room 4230
2015 Linden Drive West
Madison, WI 53706-1102
$16.00 per sample plus $4.00 per accession. An accession is all samples submitted at the same time by a single veterinarian from a single herd.
Results of radiometric culture are available 8 weeks after receiving the sample.
Mycobacterial isolates can presumptively be identified as M. paratuberculosis at
8 weeks, however, DNA probe testing of each isolate is recommended to confirm the
identification. This requires an additional 3 weeks.
For more information call the Johne's Testing Center: 608-26-JOHNE (608-265-6463).
