Rapid Detection of Mycobacterium tuberculosis Resistance to Second-Line Drugs by Use of the Manual Mycobacterium Growth Indicator Tube System

Abstract

The objective of this study was to evaluate the manual mycobacterium growth indicator tube (MGIT) system for the testing of Mycobacterium tuberculosis susceptibility to second-line drugs compared to the proportion method. One hundred eighty-eight M. tuberculosis isolates were tested for susceptibility to ofloxacin, kanamycin, ethionamide, and capreomycin by the manual MGIT, and results were compared to those obtained with the proportion method on 7H11 agar, considered a reference method. Results for ofloxacin and capreomycin were excellent, with 100% accuracy, and a result of 99.4% accuracy was achieved for kanamycin. For ethionamide, accuracy was lower, with a result of 86.7% compared to that of the proportion method. We proposed the following critical concentrations for the drugs: for ofloxacin, 2.0 g/ml; for kanamycin, 2.5 g/ml; for ethionamide, 5 g/ml; and for capreomycin, 2.5 g/ml. The time required to obtain results was an average of 8 days by the manual MGIT and 3 weeks by the reference method. Our results show that the manual MGIT is an accurate method for the rapid susceptibility testing of M. tuberculosis to second-line drugs. There is no need for a machine when using the manual MGIT, and results can be read with a simple UV lamp or with a semiquantitative reader, which considerably reduces the cost of the method.The emergence of multidrug-resistant tuberculosis (MDR-TB) caused by Mycobacterium tuberculosis and, recently, extensively drug-resistant tuberculosis caused by an MDR strain that is also resistant to any fluoroquinolone and at least one of the three injectable second-line drugs (kanamycin [KAN], amikacin [AK], and/or capreomycin [CM]) is a real threat for TB control programs (28). It is obvious that there is a great necessity for rapid, reliable, and economical methods for testing the susceptibility of M. tuberculosis not only to first-line drugs but also to second-line drugs. Access to drug susceptibility testing (DST) is a priority, and TB culture is an essential component of TB management. Using the standardized conventional DST methods, it takes a minimum of 3 to 8 weeks to identify resistant or susceptible strains on solid media (6, 7). The introduction of liquid culture media such as the manual mycobacterium growth indicator tube (MGIT) reduces the turnaround time compared to that of solid media, taking an average of 15 days to get results (1,5,19,23,25). In June 2007, the World Health Organization issued a recommendation for the use of liquid media for culture and DST in middle-and low-income countries to address challenges due to the epidemic of human immunodeficiency virus-associated TB and drug-resistant TB, especially in resource-limited settings (29). Fully automated commercial systems such as the BACTEC MGIT 960 (Becton Dickinson) have shown their usefulness for the rapid detection of resistance to second-line drugs (12, 24); however, they require heavy equipment and are still constrained by the cost of the machines. The manual MGIT system has been reported to be a sensitive and ...

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). …”

“…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). 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).…”

Effect of temperature on storage of ethionamide during susceptibility testing

“…Hence, it is advised to use drug incorporated media judiciously as soon as it is prepared and storage might deteriorate the drug activity. 13 Ethionamide has been indicated to exhibit cross resistance with isoniazid. [14][15][16] Therefore, reliability of the ETH susceptibility testing is the need of the hour.…”

Drug-susceptibility testing in TB: current status and future prospects

“…Several studies have been published using different liquid systems for secondline DST [18][19][20][21][22][23][24]. The first evaluation studies were performed using the radiometric BACTEC 460 system for testing secondline drugs and newer antibiotics [18].…”