Comparison between the BACTEC MGIT 960 system and the agar proportion method for susceptibility testing of multidrug resistant tuberculosis strains in a high burden setting of South Africa

Abstract

BackgroundThe increasing problem of multi-drug-resistant (MDR) tuberculosis (TB) [ie resistant to at least isoniazid (INH) and rifampicin (RIF)] is becoming a global problem. Successful treatment outcome for MDR-TB depends on reliable and accurate drug susceptibility testing of first-line and second-line anti-TB drugs.MethodConsecutive M. tuberculosis isolates identified as MDR-TB during August 2007 to January 2008 using the BACTEC MGIT 960 systems and the agar proportion method were included in this study. Susceptibility testing of MDR-TB isolates against ethambutol (EMB) and streptomycin (STR) as well as two second-line anti-TB drugs, kanamycin (KAN) and ofloxacin (OFX) was performed using the BACTEC MGIT 960 systems at a routine diagnostic laboratory. The results were compared to those obtained by the agar proportion method.ResultThe agreement between the BACTEC MGIT 960 system and the agar proportion method was 44% for EMB, 61% for STR and 89% for both KAN and OFX. The sensitivity and specificity of the BACTEC MGIT 960 system using the agar proportion method as a gold standard was 92% and 37% for EMB, 95% and 37% for STR, 27% and 97% for KAN and 84% and 90% for OFX, respectively.ConclusionsThe BACTEC MGIT 960 system showed acceptable sensitivity for EMB, STR, and OFX; however, the BACTEC MGIT 960 system was less specific for EMB and STR and demonstrated a low sensitivity for KAN. The lower agreement found between the two methods suggests the unreliability of the BACTEC MGIT 960 system for the drugs tested. The reasons for the lower agreement between the two methods need to be investigated and further studies are needed in this setting to confirm the study finding.

Evaluation of the BACTEC MGIT 960 SL DST Kit and the GenoType MTBDRsl Test for Detecting Extensively Drugresistant Tuberculosis Cases

“…Zhao et al [13] studied 321 isolates (sensitivity 100% and specificity 98.6%) and Kim et al [14] studied 193 clinical isolates (sensitivity 100%, specificity 95%) using the BACTEC MGIT 960 SL DST, and their results were consistent with our results. However, Said et al [15] evaluated 343 isolates using the BACTEC MGIT 960 method and reported sensitivity of 27%, which was considerably lower than that in our study. We believe that this discordance occurred because Said et al [15] used a KAN concentration higher (5 µg/ mL) than the concentration recommended by CLSI and WHO (2.5 µg/mL) [7,8].…”

Utilidad de la prueba de la nitrato reductasa para la detección rápida de resistencia en Mycobacterium tuberculosis

“…También existen métodos comerciales más rápidos como el BACTEC ™ 460TB (16), el BACTEC ™ MGIT (17), los cuales se basan en el crecimiento bacteriano en presencia del antibiótico, y los métodos genotípicos como el INNOLipa ™ _Rif.TB (Inmunogenetics) (18), el Geno Type ™ MTBDR (Hain Lifescience, Nehren, Germany) (19) y el Xpert ™ MTB/RIF (Cepheid) (20), que evalúan la resistencia por medio de la detección de mutaciones cromosómicas, y que, a pesar de ser rápidos, requieren personal entrenado, infraestructura adecuada, reactivos y equipos sofisticados y costosos, lo que hace difícil su uso en países de recursos limitados como el nuestro (21).…”

Comparison of the Mycobacterium Growth Indicator Tube Method and the Method of Proportion for Drug Susceptibility Testing of Mycobacterium Tuberculosis

“…The highest resistance rate was detected in isolates sent from Bursa province (located in northwestern Turkey). In the same study, MDR-TB rates (18.8% and 10.6%, respectively) 16.7% and 11.7% for SM and 6.7% and 8.3% for EMB by MOP and MGIT, respectively. The MDR-TB rates detected in our study were 10% (6 strains) using MOP and 8.3% (5 strains) using MGIT.…”

“…By adding M. tuberculosis suspension to a drug-containing MGIT tubes, an anti-mycobacterial susceptibility test (AST) can be [15] found a better correlation between MGIT and MOP on LJ medium. Said et al [16] reported that the MGIT 960 system performed well for SM and EMB when compared to MOP (sensitivity in detecting resistance 95% and 92%, respectively). Safwat et al [11] reported that the total efficiency of MGIT was 82% for susceptibility testing to SM, while it was 96% for INH, 90% for RIF and 80% for EMB.…”