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

Mycobacterium avium subsp. paratuberculosis (MAP) is the causal agent of paratuberculosis, a chronic, contagious, and incurable enteric disease of ruminants. An in-house IS 900 PCR 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 IS 900 PCR assay with a commercial ISMap 02 PCR 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 IS 900 PCR 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 IS 900 PCR assay. Among culture-positive samples before incubation, the IS 900 PCR assay yielded significantly more positive results than the ISMap 02 PCR assay; however, among culture-negative samples, the IS 900 PCR assay yielded positive results both before and after incubation. The ISMap 02 PCR assay did not flag positively among the culture-negative samples either before or after incubation. The IS 900 PCR assay is a sensitive method that can be used to detect MAP DNA in environmental samples before incubation. The ISMap 02 PCR assay is a specific method used to detect MAP DNA in environmental samples both before and after incubation.