Mycobacteriology Rapid prediction of BACTEC MGIT 960 culture results by COBAS Amplicor Mycobacterium polymerase chain reaction detection Akio Aono a , Yuka Azuma a , Satoshi Mitarai b, ⁎ , Hideo Ogata c a Department of Clinical Microbiology, Double-Barred Cross Hospital, Japan Anti-Tuberculosis Association, Tokyo 204-8533, Japan b Bacteriology Division, Department of Mycobacterium Reference, Research Institute of Tuberculosis, Japan Anti-Tuberculosis Association, Tokyo 204-8533, Japan c Department of Respiratory and Internal Medicine, Double-Barred Cross Hospital, Japan Anti-Tuberculosis Association, Tokyo 204-8533, Japan Received 17 September 2008; accepted 20 January 2009 Abstract A combination of a rapid culture system, BACTEC MGIT 960 (MGIT), and a commercial polymerase chain reaction (PCR) system for the detection of Mycobacterium tuberculosis was evaluated to predict final culture results within 2 weeks. A total of 79 sputum specimens were collected from 59 tuberculosis (TB) patients before anti-TB chemotherapy. Among the 22 specimens that were smear negative and culture positive, the COBAS Amplicor nucleic amplification method for sputum resulted in 13 positives (59.1%) before culturing. In contrast, 21 liquid culture specimens (95.5%) showed positive results by COBAS Amplicor after 7 days. Similarly, 8 specimens (80%) were positive for Mycobacterium avium complex (MAC) based on COBAS Amplicor, and 10 liquid culture specimens (100%) showed positive results after 7 days. Among the 26 specimens that took more than 7 days to become positive by MGIT, 25 specimens (96.1%) were positive using COBAS Amplicor with 7-day-old cultures. Of the 26 positives, 21 were M. tuberculosis, which took 11 to 38 days to appear positive (mean, 16.6 days), and 4 were MAC, which took 8 to 10 days (mean, 8.8 days). As a result, 96.8% (31/32) of the positives could be detected by MGIT with COBAS Amplicor by day 7, and the negative predictive value was 97.9%. A combination of MGIT and COBAS Amplicor on day 7 was demonstrated as a useful method for rapid diagnosis of positives and negatives, without waiting 42 days for confirmation. © 2009 Elsevier Inc. All rights reserved. Keywords: BACTEC MGIT 960; COBAS Amplicor Mycobacterium; Mycobacterium tuberculosis 1. Introduction Tuberculosis (TB) is still a life-threatening disease. Approximately 9.1 million people develop TB and 1.7 million patients die every year (World Health Organization [WHO], 2008). The WHO has initiated and expanded directly observed treatment with short-course chemotherapy and attempts to detect 70% of the acid-fast bacilli (AFB) smear-positive patients and treats 85% of them successfully with this strategy. However, the low smear positivity in TB patients with HIV has recently resulted in a critical problem for TB diagnostics (Klein et al., 1989). Culture examination has higher sensitivity than smear microscopy and could provide a powerful diagnostic tool even with HIV-coinfected TB patients. Many mycobacterial pathogens grow slowly and take quite a long time to be detected by conventional culture methods. A rapid culturing system with liquid medium and a sensitive detection system, for example, BACTEC MGIT 960 (MGIT; Becton Dickinson, Franklin Lakes, NJ), was recently introduced and showed efficient and rapid isolation of mycobacteria from clinical specimens (Chien et al., 2000; Hanna et al., 1999; Somoskovi and Magyar, 1999; Tortoli et al., 1999). However, even by MGIT, it takes a longer time for paucibacillary specimens to be positive, and 6 weeks are needed for confirmation of negative results (Abe, 1996). Nucleic acid amplification (NAA) is a useful method for detecting targeted bacterial sequences directly from clinical specimens and is widely used to identify mycobacterial species. NAA has dramatically shortened the time required to detect mycobacteria in clinical specimens (Aoki et al., 1994). A commercial polymerase chain reaction (PCR) test, COBAS Amplicor (Roche Diagnostics Systems, Japan), is Available online at www.sciencedirect.com Diagnostic Microbiology and Infectious Disease 64 (2009) 27 – 30 www.elsevier.com/locate/diagmicrobio ⁎ Corresponding author. Tel.: +81-42-493-5762; fax: +81-42-492-4600. E-mail address: mitarai@jata.or.jp (S. Mitarai). 0732-8893/$ – see front matter © 2009 Elsevier Inc. All rights reserved. doi:10.1016/j.diagmicrobio.2009.01.011