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Journal of Clinical Microbiology, January 2007, p. 76-80, Vol. 45, No. 1
0095-1137/07/$08.00+0     doi:10.1128/JCM.00951-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Comparative Evaluation of Löwenstein-Jensen Proportion Method, BacT/ALERT 3D System, and Enzymatic Pyrazinamidase Assay for Pyrazinamide Susceptibility Testing of Mycobacterium tuberculosis{triangledown}

Pushpendra Singh,1 Clement Wesley,1,{dagger} G. P. S. Jadaun,1 Sunil Kumar Malonia,1,{ddagger} R. Das,1 P. Upadhyay,1 J. Faujdar,1 P. Sharma,1 P. Gupta,1 Abhay Kumar Mishra,1 Kalpana Singh,1 D. S. Chauhan,1 V. D. Sharma,1 U. D. Gupta,2 K. Venkatesan,3 and V. M. Katoch1*

Department of Microbiology and Molecular Biology,1 Department of Animal Experimentations,2 Department of Biochemistry, National JALMA Institute for Leprosy and Other Mycobacterial Diseases, Tajganj, Agra (Uttar Pradesh) 282001, India3

Received 6 May 2006/ Returned for modification 2 June 2006/ Accepted 23 October 2006

Pyrazinamide (PZA) is an important first-line antituberculosis drug because of its sterilizing activity against semidormant tubercle bacilli. In spite of its very high in vivo activity, its in vitro activity is not apparent unless an acidic environment is available, which makes PZA susceptibility testing difficult by conventional methods. The present study was, therefore, planned to assess the performance of the colorimetric BacT/ALERT 3D system and compare the results with those from conventional tests, i.e., the Löwenstein-Jensen (LJ) proportion method (pH 4.85) and Wayne's pyrazinamidase (PZase) assay, using 107 clinical isolates. The concordance among all of these tests was 89.71% after the first round of testing and reached 92.52% after resolution of the discordant results by retesting. Prolonged incubation of the PZase tube for up to 10 days was found to increase the specificity of the PZase test. The concordances between LJ proportion and BacT/ALERT 3D, LJ proportion and the PZase assay, and BacT/ALERT 3D and the PZase assay were found to be 99.06%, 93.46%, and 92.52%, respectively. Using the LJ results as the gold standard, the sensitivities of BacT/ALERT 3D and the PZase assay were 100 and 82.85%, respectively, while the specificity was 98.61% for both of the tests. The difference between the sensitivities of BacT/ALERT 3D and the PZase assay was significant (P = 0.025). The mean turnaround times for the detection of resistant and susceptible results by BacT/ALERT 3D were 8.04 and 11.32 days, respectively. While the major limitations associated with the PZase assay and the LJ proportion method are lower sensitivity in previously treated patients and a longer time requirement, respectively, the BacT/ALERT 3D system was found to be rapid, highly sensitive, and specific.

* Corresponding author. Mailing address: National JALMA Institute for Leprosy and Other Mycobacterial Diseases (ICMR), Tajganj, Agra (Uttar Pradesh) 282001, India. Phone: 91 562 223 2222. Fax: 91 562 233 1755. E-mail: vishwamohan_katoch{at}yahoo.co.in.

{triangledown} Published ahead of print on 8 November 2006.

{dagger} Present address: Virology Group, International Center for Genetic Engineering and Biotechnology, New Delhi, India.

{ddagger} Present address: National Center for Cell Sciences, Ganeshkhind, Pune, India.

Journal of Clinical Microbiology, January 2007, p. 76-80, Vol. 45, No. 1
0095-1137/07/$08.00+0     doi:10.1128/JCM.00951-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.





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