Automated liquid culture system misses isoniazid heteroresistance in Mycobacterium tuberculosis isolates with mutations in the promoter region of the inhA gene

Rapid Diagnosis Of Multidrug-Resistant Tuberculosis Impacts Expenditures Prior To Appropriate Treatment: A Performance And Diagnostic Cost Analysis

Background

In this study, we aimed to describe the impact of the Genotype® MTBDRplus line probe assay (LPA) for multidrug-resistant tuberculosis (MDR-TB) on total costs in a high-burden setting in China. The second objective was to evaluate the performance of HAIN on smear-positive sputum and clinical isolates.

Methods

All definitive TB inpatients at the Shandong Provincial Chest Hospital between May 2012 and May 2017 were included in the study. Two sputum specimens were collected from each patient to conduct smear microscopy, conventional drug susceptibility testing (DST), and the HAIN test. Laboratory and cost data were collected from the electronic medical record system.

Results

A total of 1670 definitive TB patients were included in this study. Of these patients, 1307 (78.3%) had smear-positive/culture-positive tuberculosis, and the remaining 363 (21.7%) had smear-negative/culture-positive tuberculosis. The sensitivity and specificity of the HAIN test for RIF resistance was 94.8% (95% confidence interval [CI]: 91.9-97.6%) and 98.8% (95% CI: 98.3-99.4%), respectively. For INH resistance, the sensitivity and specificity was 89.5% (95% CI: 85.7-93.2%) and 95.6% (95% CI: 94.5-96.7%), respectively. The mean time for detection of MDR-TB in smear-negative cases was determined to be 32 days by the HAIN test, which was significantly shorter than that by conventional DST (56 days). Similarly, the mean time for detection of MDR-TB by the HAIN test was significantly shorter than that by conventional DST in smear-positive cases (3 versus 53 days). In addition, by utilizing the HAIN test, the total health care cost decreased by 71.0% for smear-positive cases and 25.9% for smear-negative cases.

Conclusion

In conclusion, our data demonstrate that the HAIN test is an accurate rapid test for detecting both RIF and INH resistance in TB patients. The use of the HAIN test can decrease health care costs and reduce the detection time for MDR-TB patients in China, despite the increased costs for laboratory testing.

Agreement of Middle brook 7H10 with Lowenstein Jensen and accuracy of the Sensititre MYCOTB plate using either method as a reference standard for Mycobacterium tuberculosis first line drug susceptibility testing

INTRODUCTION

Although Sensititre Mycobacterium tuberculosis (MYCOTB) plate offers both drug susceptibility testing (DST) and minimum inhibitory concentration (MIC) results, it has not been evaluated against both Lowenstein Jensen (LJ) and Middlebrook 7H10 (MB7H10) DST methods at standard critical concentrations.

MATERIALS AND METHODS

We analyzed 76 M. tuberculosis isolates consisting of 54 isolates from the Uganda National TB drug resistance survey done December 2009-February 2011 and 22 isolates from the World Health Organization External Quality Assessment panel for the year 2011. All isolates were tested for LJ, MB7H10 and MYCOTB plate based DSTs for streptomycin, isoniazid, rifampicin and ethambutol anti-tuberculosis drugs. The agreement of MB7H10 with LJ and accuracy of MYCOTB plate using either LJ-DST or MB7H10 as a reference standard were determined.

RESULTS

The agreement (kappa) of MB7H10 with LJ was; 0.687 for rifampicin, 0.498 for isoniazid, 0.275 for streptomycin and 0.082 for ethambutol which as almost similar when compared with MYCOTB plate. The sensitivity (95% confidence interval; CI) of MYCOTB plate when LJ was used as a reference standard was higher for streptomycin 87.5% (81.6-98.4) followed by isoniazid 75.9% (65.1-95.6) and rifampicin 73.1% (52.2-88.4). When MB7H10 was used as reference standard, the sensitivity of MYCOTB plate improved significantly; isoniazid 96.2% (80.3-99.9), rifampicin 94.0 (83.4-98.7) and 93.8% (69.7-99.8). There was good agreement between MYCOTB plate and MB7H10; 1.00 for ethambutol, 0.959 for streptomycin, 0.915 for rifampicin and 0.778 for isoniazid.

CONCLUSIONS

The performance of the two culture-based reference standards for phenotypic first-line drug susceptibility testing methods, LJ and MB7H10, varied much even with acceptable MYCOTB plate MICs. There was acceptable agreement and accuracy of MYCOTB plate for drug susceptibility testing when MB7H10 was used as reference standard than with LJ-DST. Results from MIC information makes the MYCOTB plate more suitable for guiding clinicians on the choice of the most appropriate TB treatment regimen as well as limits of detection for TB drug resistance.

Examination of bedaquiline- and linezolid-resistant Mycobacterium tuberculosis isolates from the Moscow region

Objectives

To study the isolates with acquired resistance to bedaquiline and linezolid that were obtained from patients enrolled in a clinical study of a novel therapy regimen for drug-resistant TB in Moscow, Russia.

Methods

Linezolid resistance was detected using MGIT 960 with a critical concentration of 1 mg/L. The MIC of bedaquiline was determined using the proportion method. To identify genetic determinants of resistance, sequencing of the mmpR ( Rv0678 ), atpE , atpC , pepQ , Rv1979c , rrl , rplC and rplD loci was performed.

Results

A total of 85 isolates from 27 patients with acquired resistance to linezolid and reduced susceptibility to bedaquiline (MIC ≥0.06 mg/L) were tested. Most mutations associated with a high MIC of bedaquiline were found in the mmpR gene. We identified for the first time two patients whose clinical isolates had substitutions D28N and A63V in AtpE, which had previously been found only in in vitro -selected strains. Several patients had isolates with elevated MICs of bedaquiline prior to treatment; four of them also bore mutations in mmpR , indicating the presence of some hidden factors in bedaquiline resistance acquisition. The C154R substitution in ribosomal protein L3 was the most frequent in the linezolid-resistant strains. Mutations in the 23S rRNA gene (g2294a and g2814t) associated with linezolid resistance were also found in two isolates. Heteroresistance was identified in ∼40% of samples, which reflects the complex nature of resistance acquisition.

Conclusions

The introduction of novel drugs into treatment must be accompanied by continuous phenotypic susceptibility testing and the analysis of genetic determinants of resistance.

Rapid diagnosis of MDR and XDR tuberculosis with the MeltPro TB assay in China

New diagnostic methods have provided a promising solution for rapid and reliable detection of drug-resistant TB strains. The aim of this study was to evaluate the performance of the MeltPro TB assay in identifying multidrug-resistant (MDR-) and extensively drug-resistant tuberculosis (XDR-TB) patients from sputum samples. The MeltPro TB assay was evaluated using sputum samples from 2057 smear-positive TB patients. Phenotypic Mycobacterial Growth Indicator Tube (MGIT) 960 drug susceptibility testing served as a reference standard. The sensitivity of the MeltPro TB assay was 94.2% for detecting resistance to rifampicin and 84.9% for detecting resistance to isoniazid. For second-line drugs, the assay showed a sensitivity of 83.3% for ofloxacin resistance, 75.0% for amikacin resistance, and 63.5% for kanamycin resistance. However, there was a significant difference for detecting kanamycin resistance between the two pilot sites in sensitivity, which was 53.2% in Guangdong and 81.5% in Shandong (P = 0.015). Overall, the MeltPro TB assay demonstrated good performance for the detection of MDR- and XDR-TB, with a sensitivity of 86.7% and 71.4%, respectively. The MeltPro TB assay is an excellent alternative for the detection of MDR- and XDR-TB cases in China, with high accuracy, short testing turn-around time, and low unit price compared with other tests.