Multicenter Evaluation of Bactec MGIT 960 System for Second-Line Drug Susceptibility Testing of Mycobacterium tuberculosis Complex

Abstract

The Bactec MGIT 960 system for testing susceptibility to second-line drugs was evaluated with 117 clinical strains in a multicenter study. The four drugs studied were levofloxacin, amikacin, capreomycin, and ethionamide. The critical concentration established for levofloxacin and amikacin was 1.5 g/ml, that established for capreomycin was 3.0 g/ml, and that established for ethionamide was 5.0 g/ml. The overall level of agreement between the agar proportion method and the MGIT 960 system was 96.4%, and the levels of agreement for the individuals drugs were 99.1% for levofloxacin, 100% for amikacin, 97.4% for capreomycin, and 88.9% for ethionamide. The rate of reproducibility of the drug susceptibility testing results between the participating laboratories was 99.5%.The increase in the incidence of multidrug-resistant tuberculosis (MDR TB) and the emergence of extensively drugresistant tuberculosis present tremendous challenges to the global efforts to combat tuberculosis (1,5,16,21). Rapid methods enabling accurate susceptibility testing of first-line and second-line drugs are critical for the early diagnosis of MDR TB and extensively drug-resistant tuberculosis and the initiation of effective regimens. Various drug susceptibility testing (DST) methods that use solid media, including the agar proportion method (AP) and other methods, have the drawback of prolonged turnaround times (TATs). The World Health Organization and the U.S. Centers for Disease Control and Prevention have recommended the use of liquid culture systems for the diagnosis of tuberculosis and DST to improve TATs (22,25). The Bactec 460 (Becton Dickinson Diagnostic Systems, Sparks, MD), a radiometric liquid system, provided an excellent alternative for testing of the susceptibilities of Mycobacterium tuberculosis complex (MTBC) isolates to streptomycin, isoniazid, rifampin (rifampicin), and ethambutol (SIRE) and to pyrazinamide (PZA) with improved TATs. The MGIT 960 liquid, nonradiometric SIRE DST (Becton Dickinson Diagnostic Systems), whose performance is comparable to that of the Bactec 460 system, has been commercially available since April 2002 (4, 20, 23). The Microbial Diseases Laboratory (MDL) of the California Department of Public Health implemented SIRE DST with the MGIT 960 system in 2004. With confidence in the SIRE DST with the MGIT 960 system, a study that used the same platform to test the susceptibilities of MTBC isolates to four classes of second-line drugs, levofloxacin (LVX), amikacin (AMK), capreomycin (CAP), and ethionamide (ETH), was initiated in November 2004. The study was conducted at two laboratories: MDL and the TB Reference Laboratory of the Veteran Affairs Medical Center (VA) in West Haven, CT. Here we report the results of the multicenter study, in which the critical concentrations of the test drugs were established, the performance of the MGIT 960 system was compared to that of AP, and the interlaboratory reproducibility of the method was evaluated.(Part of this work was presented at the 46th Interscience Conference...

Clinical Laboratory Diagnostics for Mycobacterium tuberculosis

“…Similar results were obtained in a study comparing the manual version of the MGIT to the agar method using the second-line drugs ofloxacin, kanamycin, ethionamide, and capreomycin (Martin et al, 2008). In both studies, the agreement between the two methods for ethionamide was markedly lower (86-88%) than for the other drugs (Martin et al, 2008;Lin et al, 2009). …”

“…Evaluation of the MGIT performance for the primary tuberculosis drugs showed results that were comparable to the BACTEC 460 radiometric methods as well as the agar proportion methods (>90% agreement) (Ardito et al, 2001;Adjers-Koskela & Katila, 2003;Scarparo et al, 2004), except for EMB and STR which had agreement varying from less than 80% to 98% (Adjers-Koskela & Katila, 2003;Scarparo et al, 2004;Hall et al, 2006;Garrigo et al, 2007). More recently, the MGIT 960 was evaluated for susceptibility testing of second-line drugs including levofloxacin, amikacin, capreomycin and ethionamide with overall agreement of 96% at critical concentrations when compared to the agar proportion method (Lin et al, 2009). Similar results were obtained in a study comparing the manual version of the MGIT to the agar method using the second-line drugs ofloxacin, kanamycin, ethionamide, and capreomycin (Martin et al, 2008).…”

Cost-effectiveness in the diagnosis of tuberculosis: choices in developing countries

“…The use of this system has not been cleared by the FDA for DST of second-line drugs, and thus most laboratories rely on agar proportion as the reference standard. Moreover, many studies have demonstrated that the performance of BACTEC MGIT 960 for DST of second-line drugs was comparable to the agar proportion method; the system is therefore a reliable tool for detecting resistance to second-line drugs [33]. With the purpose of detecting drug resistance in a shorter time, several molecular approaches have been proposed.…”

A Simple and Rapid Liquid Chromatography Method for Determination of Levofloxacin in Plasma

“…The minimal inhibitory concentration (MIC 90 ) of LFX against M.tuberculosis is 0.5µg/ml. 20 After a daily oral dose of 1000 mg LFX, the mean maximum plasma concentration of LFX at steady state is 8.24 µg/ml; this is attained at 2 hours post-dosing. 21 In the present method, LFX concentrations ranging from 0.25-10.0µg/ml were checked for linearity.…”