A DNA probe for the detection of Mycobacterium paratuberculosis

Preparation of a specific RNA probe for detection of Mycobacterium paratuberculosis and diagnosis of Johne's disease

A species-specific recombinant clone (F57) was obtained from a genomic library of Mycobacterium paratuberculosis in the transcription vector pGem 3Z. This clone proved to be specific for all mycobacteria tested, including M. avium, and was able to recognize all of the tested M. paratuberculosis strains isolated from animals and humans (patients with Crohn's disease). The F57 insert was sequenced and a segment of 620 bp with a G + C content of 58.9% was identified. Comparison of the sequence with sequences in the EMBL and UGEN data banks revealed the uniqueness of the F57 sequence, which had no resemblance to other known genes.

Comparison of a commercial DNA probe test and three cultivation procedures for detection of Mycobacterium paratuberculosis in bovine feces

Diagnosis of paratuberculosis using the IDEXX DNA probe test and 3 methods for cultivation of Mycobacterium paratuberculosis from fecal specimens were compared. Twenty-one of 170 fecal specimens were DNA probe test positive, whereas 35 specimens were positive by 1 or more of the cultivation methods evaluated. Four specimens were DNA probe test positive but were negative by fecal culture. The probe test detected M. paratuberculosis DNA in 62.9% of the specimens positive by a sedimentation culture method, in 56.6% of those positive by a centrifugation culture method, and in 65.4% of the specimens positive by the Cornell culture method. Specificity of the DNA probe test was approximately 97% relative to all culture methods. Generally, the probe test detected M. paratuberculosis DNA in fecal specimens from animals shedding at least 10(4) M. paratuberculosis colony forming units per gram of feces. Although the probe test did not detect all of the cattle shedding M. paratuberculosis, it was possible to identify cattle shedding the greatest number of organisms in 3 days compared with a minimum of 6 weeks required for positive culture results. The centrifugation method resulted in the most isolations of M. paratuberculosis after 12 weeks of incubation. However, contamination also was greatest when the centrifugation method was used. Contamination was best controlled using the Cornell method. The sedimentation method was the least time consuming and yielded results similar to those of the other 2 methods.