Polymerase chain reaction identification of Mycobacterium avium in formalin-fixed, paraffin-embedded animal tissues

A PCR procedure previously developed for identification of Mycobacterium, b ovis in formalin-fixed tissues was used to identify mycobacteria of the M. avinm complex. Tissues were examined from 100 culture-positive cases of M. avium complex infection, including 86 in which the subspecies was not ident ified and 14 that had been identified as M. avium subsp. paratuberculosis. Each sample was tested with 5 primer sets, 16S ribosomal RNA (rRNA), IS900, IS901, IS1245, and a heat shock protein (hspX), that detect 1 or both M. a vium subspecies. The success rate of PCR detection varied with the primers used and the animal species tested. Among the 86 cases with no M. avium sub species designation, primers for the 16S rRNA gene were clearly the most ef ficient because they produced amplicons from all samples that reacted with any other primer set. The overall detection rate in this group of samples w as 71%: highest in avian tissues (89%) followed by swine (72%) and ruminant s (57%) None of the avian or swine tissues reacted with primers for IS900 o r hspX, which identify M. a. parantuberculosis. In contrast, 7 of the 12 ru minant samples that were 16S rRNA positive reacted with 1 or both of these primers. All of the 14 cases shown by culture to be M. a, parantuberculosis infections were positive with IS900 primers, whereas only 11 were positive for 16S rRNA. These results indicate that 16S rRNA primers are the most us eful for PCR identification of M. avium in formalin-fixed tissues of nonrum inant species. However, IS900 primers should also be used when ruminant tis sues are examined because these primers provide the,greatest sensitivity fo r detection of M. a. paratuberculosis infections.