Canadian Multicenter Laboratory Study for Standardized Second-Line Antimicrobial Susceptibility Testing of Mycobacterium tuberculosis

Abstract

The purpose of this study was to establish a standardized protocol for second-line antimicrobial susceptibility testing of Mycobacterium tuberculosis using the Bactec MGIT 960 system in Canadian laboratories. Four Canadian public health laboratories compared the susceptibility testing results of 9 second-line antimicrobials between the Bactec 460 and Bactec MGIT 960 systems. Based on the data generated, we have established that the Bactec MGIT 960 system provides results comparable to those obtained with the previous Bactec 460 method. The critical concentrations established for the testing of the antimicrobials used are as follows: amikacin, 1 g/ml; capreomycin, 2.5 g/ml; ethionamide, 5 g/ml; kanamycin, 2.5 g/ml; linezolid, 1 g/ml; moxifloxacin, 0.25 g/ml; ofloxacin, 2 g/ml; p-aminosalicylic acid, 4 g/ml; rifabutin, 0.5 g/ml.The Public Health Agency of Canada (PHAC) publishes yearly statistics on the antimicrobial resistance patterns of all laboratory-isolated Mycobacterium tuberculosis strains in Canada. From 2000 to 2010, the number of M. tuberculosis isolates resistant to one or more of the first-line antimicrobials has varied between 8.0% and 11.0% of all tuberculosis (TB) cases per year in Canada (15). Between 0.9% and 1.6% of these cases were considered multidrug resistant (MDR) TB. Since 2005, TB cases in the foreign-born Canadian population have accounted for more than 60% of all Canadian TB cases and greater than 90% of MDR TB cases (10-14).Currently it is recommended that after systematic testing against first-line anti-TB agents, isolates that are found to be monoresistant to rifampin or to demonstrate resistance to any two of the first-line antimicrobials be tested against a panel of secondline antimicrobials (3,7,21). Though the majority of resistant isolates in Canada show monoresistance to isoniazid (INH), recently published Clinical and Laboratory Standards Institute (CLSI) document M24-A2 recommends that second-line antimicrobial testing also be performed on isolates that are INH monoresistant in cases where fluoroquinolones may be added to the therapy. The current standard method for first-line antimicrobial sensitivity testing (AST) of M. tuberculosis in Canada is the Bactec MGIT 960 (M960) system (BD, Sparks, MD). Although the M960 system has been approved for first-line AST (2-4, 20), the Bactec 460 (B460; BD, Sparks, MD) and the agar proportion method are currently used for second-line AST since the M960 system had not been validated for this purpose (3,8). Due to the increasing demand for second-line AST and the discontinuation of the B460 technology by the manufacturer, a multicenter validation of a second-line AST panel for the M960 system was undertaken. A validated and standardized method and antimicrobial panel for second-line AST are required to ensure that antimicrobial-resistant cases of M. tuberculosis, including MDR and extensively drug-resistant cases, are identified in an accurate and timely manner and that susceptibility testing and reporting of these isolates are standardize...

Evaluation of BACTEC MGIT 960 system for the second-line drugs susceptibility testing of Mycobacterium tuberculosis in China

“…This meant BACTEC MGIT 960 system had the tendency to generate ME rather than VME for the second-line drugs susceptibility testing. This phenomenon hadn't been demonstrated in the previous reports based on the second-line drugs susceptibility testing evaluations between BACTEC MGIT 960 system and BACTEC MGIT 460 system (Rusch-Gerdes et al, 2006;Rodrigues et al, 2008;Sharma et al, 2011). However, it is not surprising that results obtained from these two liquid-medium based systems are consistent with each other because both systems are made by the same company.…”

“…Most reports focused on the comparison between BACTEC MGIT 960 system and BACTEC MGIT 460 system (Rusch-Gerdes et al, 2006;Rodrigues et al, 2008;Sharma et al, 2011). There are also several papers available for the second-line drugs susceptibility testing between BACTEC MGIT 960 system and agar PM (AP) (Kruuner et al, 2006;Lin et al, 2009;van Ingen et al, 2010).…”

“…It could automatically report the drug susceptibilities according to the predefined algorithms in 4-13 days after inoculation. Recently, some researchers used this platform for the second-line drugs susceptibility testing of tuberculosis and established the second-line drugs critical concentrations and procedures of BACTEC MGIT 960 system referring to BACTEC MGIT 460 system (Kruuner et al, 2006;Rusch-Gerdes et al, 2006;Rodrigues et al, 2008;Lin et al, 2009;Sharma et al, 2011). Despite the arrival of this novel tool, it remains uncertain that if the second-line drugs susceptibility testing with BACTEC MGIT 960 system is suitable for the diagnosis of resistant-TB in China without being evaluated in comparative studies.…”

Emergence and Spread of Extensively and Totally Drug-Resistant Tuberculosis, South Africa

“…Second-line DST was done in 7H10 medium containing 2 µg/mL of ofloxacin, 4 µg/mL of amikacin, or 5 µg/mL of ethionamide. DST for para -aminosalicylic acid was done at Stellenbosch University in MGIT 960 medium containing 4.0 µg/mL, 8 µg/mL, and 16 µg/mL of para -aminosalicylic acid ( 15 ). …”

A Comparison of the Sensititre MycoTB Plate, the Bactec MGIT 960, and a Microarray-Based Molecular Assay for the Detection of Drug Resistance in Clinical Mycobacterium tuberculosis Isolates in Moscow, Russia

“…The MTB DST for streptomycin (STR), pyrazinamide (PZA), RMP, INH, EMB, ofloxacin (OFX), moxifloxacin (MFX), kanamycin (KAN), amikacin (AMK), PAS, and ethionamide (ETH) was performed using a Bactec MGIT 960 as previously described [21, 22]. …”