Comparison of 2 PCR assays on environmental samples cultured for Mycobacterium aviumsubsp. paratuberculosis

Mycobacterium aviumsubsp. paratuberculosis(MAP) is the causal agent of paratuberculosis, a chronic, contagious, and incurable enteric disease of ruminants. An in-house IS900PCR assay validated for MAP detection in sheep has been shown to have a higher sensitivity than a commercial PCR and fecal culture. We have now compared the performance of this in-house IS900PCR assay with a commercial ISMap02PCR assay for the detection of MAP DNA in bovine dairy farm environmental samples. We purposefully selected 30 culture-positive, 62 culture-negative, and 62 non-interpretable environmental samples. We applied the IS900PCR assay directly to the frozen inoculum of these samples. Inocula were incubated in an automated system, and growth was confirmed by an acid-fast bacilli stain and the IS900PCR assay. Among culture-positive samples before incubation, the IS900PCR assay yielded significantly more positive results than the ISMap02PCR assay; however, among culture-negative samples, the IS900PCR assay yielded positive results both before and after incubation. The ISMap02PCR assay did not flag positively among the culture-negative samples either before or after incubation. The IS900PCR assay is a sensitive method that can be used to detect MAP DNA in environmental samples before incubation. The ISMap02PCR assay is a specific method used to detect MAP DNA in environmental samples both before and after incubation.