Evaluation of Amplicor- and IS6110-PCR for direct detection of Mycobacterium tuberculosis complex in Singapore

One hundred and seventy-eight samples from 168 individuals were tested for Mycobacterium tuberculosis complex (Mtc) using Amplicor PCR, IS6110-PCR (in-house), acid fast (AF)-staining and culture. Thirty-one samples were positive by culture, but 37 samples were later resolved to be truly positive for Mtc. Of these, Amplicor detected 32 (86.5%), IS6110-PCR detected 31 (83.6%), and AF-staining 21 (56.8%). None of the 141 Mtc-negative samples was positive by these tests, thus giving 100% specificity. Although the IS6110-PCR was more sensitive than Amplicor in detecting spiked Mtc DNA, it was not more sensitive than the latter in detecting Mtc in clinical samples. Reasons likely to account for the PCR false negativity were (i) sample inoculum size, (ii) nonuniform samples due to clumping effect of Mtc and (iii) the absence of target gene sequences for IS6110-PCR. Culture negativity, on the other hand, was likely to be associated with nonviable Mtc. Amplicor PCR is promising for direct detection of Mtc. The IS6110-PCR, however, may not be as suitable because of possible existence of IS6110-deleted Mtc strain in Singapore.