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Journal of Clinical Microbiology, July 1998, p. 2023-2029, Vol. 36, No. 7
Institut für Medizinische Mikrobiologie
und Immunologie, Städtisches Klinikum Karlsruhe, 76133 Karlsruhe,
Germany
Received 23 December 1997/Returned for modification 4 February
1998/Accepted 21 April 1998
The new Roche Cobas Amplicor Mycobacterium tuberculosis
assay, which is a semiautomated version of the manually performed Roche
Amplicor M. tuberculosis test, was compared to culture and an IS6110-based in-house PCR protocol. A total of 1,681 specimens from 833 patients, including specimen types other than
sputum, were tested in parallel by both the in-house PCR and the Cobas Amplicor M. tuberculosis assay. After we resolved
discrepant PCR results, the sensitivity, specificity, and positive and
negative predictive values for the Cobas Amplicor M. tuberculosis assay were 66.33, 99.71, 94.36, and 97.66%,
respectively. The corresponding values for the in-house PCR were 91.08, 99.85, 97.87, and 99.37%, respectively. For culture- and
smear-positive specimens, the sensitivity of the Cobas Amplicor
M. tuberculosis test was 96.42% (in-house PCR, 100%). If
only smear-negative sputum specimens were considered, the Cobas
Amplicor M. tuberculosis assay exhibited a sensitivity of
45.45% (in-house PCR, 63.63%) relative to that of culture. With a
modified protocol for DNA extraction (washing of samples plus
ultrasonication), both PCR methods performed better with gastric
aspirates than with sputum samples (sensitivity of the Cobas Amplicor
M. tuberculosis assay with smear-negative gastric aspirates, 70.00%; sensitivity of in-house PCR, 90.00%). With dithiothreitol being used for liquefaction of specimens in this study,
the Cobas Amplicor M. tuberculosis assay exhibited an
inhibition rate of 9.16%. In our view, the new Cobas Amplicor M. tuberculosis test (i) is well suited for typing of smear-positive
specimens, (ii) may also be applied to gastric aspirates and other
types of specimens if DNA extraction methods are modified
appropriately, and (iii) exhibits a sensitivity with smear-negative
sputum specimens which makes it recommendable that a minimum of three
samples from the same patient be tested.
0095-1137/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Comparison of Roche Cobas Amplicor Mycobacterium
tuberculosis Assay with In-House PCR and Culture for Detection
of M. tuberculosis
*
Corresponding author. Present address:
Westfälische Wilhelms-Universität, Institut für
Medizinische Mikrobiologie, Klinische Virologie, von Stauffenbergstr.
36, 48151 Münster, Germany. Phone: (49) 251-7793-0. Fax: (49)
251-7793-104. E-mail: eingb{at}uni-muenster.de.
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