Increased sensitivity of Mycobacterium tuberculosis Cobas Amplicor PCR following brief incubation of tissue samples on Löwenstein-Jensen substrate.

The sensitivity of Mycobacterium tuberculosis Cobas Amplicor PCR (MTB-PCR) is considerably lower for tissue than for airway samples, depending on both lower bacterial content and presence of inhibitory substances in tissues. The aim of this study was to improve the sensitivity of MTB-PCR in inhibiting biopsy samples. A brief-culture method was applied to 33 inhibitory tissue samples out of 356 obtained in Laboratory I, and compared with 44/197 such samples treated by dilution in Laboratory II. We found that 2-3 days' incubation on Löwenstein-Jensen substrate (LJ) significantly increased the sensitivity of MTB-PCR in samples exerting PCR inhibition. Sensitivity was 63% before and 92% following brief-culture of inhibitory tissue samples in Lab I, compared to 46% and 50%, respectively, with dilution in Lab II. Thus, dilution did not significantly increase sensitivity in inhibiting samples. Specificities were 99.4/99.4 and 99.2/98.2, respectively. The higher sensitivity attained by the LJ-method was probably due to diffusion of inhibiting substances into the substrate, as well as to increase in numbers of bacteria after the brief-culture. This method adds substantially to the value of MTB-PCR of biopsy material.