Evaluation of BACTEC MGIT 960 System for Testing Susceptibility of Mycobacterium tuberculosis to First-Line Drugs in China

Abstract

BackgroundThe purpose of this study was to evaluate the performance of the BACTEC MGIT 960 (M960) system compared with the proportion method (PM) on Löwenstein-Jensen (L-J) medium in a peripheral laboratory in China for the testing of Mycobacterium tuberculosis (MTB) susceptibility to streptomycin (SM), isoniazid (INH) rifampicin (RIF) and ethambutol (EMB) a combination known as SIRE.MethodsThe susceptibility of 205 clinical isolates of MTB to SM, INH, RIF and EMB was performed with the M960 system. The drugs were tested at the following concentrations: 1.0 µg/ml for SM, 0.1 µg/ml for INH, 1.0 µg/ml for RIF, and 5.0 µg/ml for EMB. The results were compared with those obtained by the L-J PM. The L-J PM at an arbiter site was used to resolve any discordant results.ResultsThe overall consistency was 96.6% and concordance values were 95.6% for SM, 97.6% for INH, 98.0% for RIF and 95.1% for EMB. The overall sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of the M960 system for PM (the standard method) was 95.6%, 97.3%, 96.2% and 96.9% respectively, and the sensitivity were 93.3% for SM, 96.9% for INH, 97.4% for RIF and 94.6% for EMB, the specificity were 96.9% for SM, 98.2% for INH, 98.4% for RIF and 95.5% for EMB, the PPV were 94.6% for SM, 97.9% for INH, 97.4% for RIF and 94.6% for EMB, the NPV were 96.2% for SM, 97.3% for INH, 98.4% for RIF and 95.5% for EMB. The turnaround time with the M960 system (median 8.0 days, ranged from 5 to 14 days) was significantly shorter than that with the PM (28 days or 42 days).ConclusionThere was a substantial degree of agreement between the two methods. The M960 system was a reliable and rapid method for SIRE susceptibility testing of tuberculosis in China.

Rapid Detection of Mycobacterium tuberculosis Strains Resistant to Isoniazid and/or Rifampicin: Standardization of Multiplex Polymerase Chain Reaction Analysis

“…40 Our results showed a sensitivity of 100% for rifampicin resistance associated to rpoB S531L and H526Y, in comparison to the 92% of Bactec MGIT 960 culture, 41 100% of GenoType MTBC test (HAIN Lifescience), 42 and an overall sensitivity 98.9% for GeneXpert platform (Cepheid, Sunnyvale, CA). 43 In the case of isoniazid resistance, our results showed an overall sensitivity of 98% in comparison to 97% of Bactec MGIT 960 culture 44,45 and 100% of GenoType MTBC test (HAIN Lifescience) (Hillemann and others, 2007). 46 Combined, our two multiplex assays reached a specificity of 96% for identifying mutants in rpoB in comparison to the Bactec MGIT 960 culture (100%), GenoType MTBC test (98%) 42 and the overall specificity of GeneXpert platform (99.8%) (Cepheid).…”

Outcomes of pulmonary tuberculosis in patients with discordant phenotypic isoniazid resistance testing

“…Accordingly, in our institution, all first isolates of M. tuberculosis complex bacteria in patients with culture-proven TB have undergone DST on both liquid and solid media since 2009. Discordant DST results between the two types of media have been well characterized, and depend on the particular drug tested [6,9,[16][17][18]25]. The test concentrations for each drug are different among the media [26,27], and this could contribute to the discrepant results among the DST methods.…”

“…Culturing and DST in liquid medium were performed using a mycobacterial growth indicator tube (MGIT) 960 SIRE kit (Becton Dickson, Sparks, MD, USA) for INH and RMP. The critical drug concentrations were 0.1 μg/ml for INH-R and 1.0 μg/ml for RMP-R [16,23]. If discordant DST results occurred between two methods, we repeated DST with subcultured isolates to exclude contamination.…”

“…Complicating this issue, some DST results are discrepant between solid versus liquid medium culture-based systems. The discrepancy rates have been reported to range from 2.4 to 7.4% for INH and 0.4-2.8% for rifampicin (RMP) [6,[16][17][18]. Furthermore, isolates with discrepant DST results between solid versus liquid media could harbor resistance-conferring mutations in the bacillary genome, which have been linked to low-level resistance in phenotypic DST [17,19,20].…”

The reliability analysis of Xpert-positive result for smear-negative and culture-negative specimen collected from bone and joint tuberculosis suspects

“…The reliability analysis of Xpert-positive result for smear-negative and culture-negative specimen collected from bone and joint tuberculosis suspects culturing. However, low sensitivity of smear testing and the time consuming characterization of culture make them suboptimal for TB diagnosis (2)(3)(4)(5).…”