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Background: Rapid diagnosis of drug-resistant Mycobacterium tuberculosis is a challenge in low-income countries. Phenotypic drug susceptibility testing using Sensititre® MycoTB assay and the resazurin microtitre plate assay (REMA) are relatively new innovative methods to determine drug susceptibility. Objectives: This study aimed to determine the performance of the Sensititre and REMA for M. tuberculosis drug susceptibility testing in a high-volume tuberculosis reference laboratory. Methods: A laboratory-based study was performed at the Inkosi Albert Luthuli Central Hospital Tuberculosis Laboratory from January 2014 to June 2015. The Sensititre® MycoTB plate and REMA were compared to the gold standard agar proportion method (APM) using 134 stored isolates. Results: Agreement between the Sensititre® MycoTB plate and APM was observed with 98% sensitivity, 82% specificity, 94% positive and 93% negative predictive values of the Sensititre® MycoTB assay for the detection of rifampicin resistance and 97%, 96%, 99% and 88% for isoniazid resistance. Good categorical agreement between the REMA and the APM was observed among isolates with 89% sensitivity, 68% specificity, 89% positive and 68% negative predictive value for the detection of rifampicin resistance and 95%, 96%, 99% and 81% for isoniazid resistance. Results for the second-line drugs showed elevated minimum inhibitory concentrations for multidrug-resistant and extensively drug-resistant tuberculosis isolates. Conclusion: The REMA and Sensititre® MycoTB plate are attractive alternatives to the gold standard APM for the phenotypic detection of M. tuberculosis drug resistance.

Objective: The present study aimed to evaluate the performances of the BACTEC MGIT 960 SL DST kit and the GenoType MTBDRsl test for detecting second-line antituberculosis drug resistance in Multidrug-resistant TB (MDR-TB) cases. Materials and Methods: Forty-six MDR-TB strains were studied. Second-line antituberculosis drug resistances were detected using the BACTEC MGIT 960 SL DST kit and the GenoType MTBDRsl test. The Middlebrook 7H10 agar proportion method was used as the reference test. Results: The sensitivity and specificity values for the BACTEC MGIT 960 SL DST kit were both 100% for amikacin, kanamycin, capreomycin (4 µg/mL), and ofloxacin; 100% and 95.3%, respectively, for capreomycin (10 µg/mL); and 85.7% and 100%, respectively, for moxifloxacin (0.5 µg/mL). The sensitivity and specificity values for the GenoType MTBDRsl test to detect fluoroquinolone and aminoglycoside/cyclic peptide resistance were 88.9% and 100%, respectively, for ofloxacin and 85.7% and 94.9%, respectively, for moxifloxacin (0.5 µg/mL). The accuracy of the GenoType MTBDRsl assay for kanamycin, capreomycin, ofloxacin, and moxifloxacin was lower than that of the BACTEC MGIT 960 SL DST. Conclusion: The BACTEC MGIT 960 SL DST kit and the GenoType MTBDRsl were successful in detecting second-line antituberculosis drug resistance. Preliminary results of the GenoType MTBDRsl are very valuable for early treatment decisions, but we still recommend additional BACTEC MGIT 960 SL DST kit usage in the routine evaluation of drug-resistant tuberculosis. [ABSTRACT FROM AUTHOR]

Background: Tuberculosis (TB) is a disease of poverty that contributes significantly to ill-health in developing countries. Drug resistant TB is a major challenge to disease control. Early diagnosis and rapid determination of drug sensitivity is of paramount importance in eradication of TB. Although automated liquid culture based methods are available for rapid detection of drug resistance, the high cost of these tests prevent them from being used routinely in low resource settings. This study compares two phenotypic methods, the manual Mycobacteria Growth Indicator Tube (MGIT) and the Nitrate Reductase Assay (NRA) in liquid medium, with the agar proportion method (APM), the gold standard for susceptibility testing of Mycobacterium tuberculosis. Methodology: Fourteen day old M. tuberculosis strains (n=373) grown on solid media were used for drug susceptibility testing by APM, NRA and the manual MGIT method. Rifampicin free and rifampicin incorporated (final concentration, 1 µg/ml) media were inoculated with the recommended concentrations of mycobacterial suspensions and incubated at 37°C in 5% CO2. In the APM, the proportion of colonies in the drug containing medium was determined. In the NRA, the colour change in the medium was compared with a standard colour series after day 6 and day 12 of incubation. Growth in the MGIT was detected using the manual MGIT reader from day 2 onwards. The 2 methods were compared with the gold standard, APM to determine sensitivity and specificity and agreement between the methods was calculated using kappa statistics. Results: Thirty one (31) rifampicin resistant isolates were identified. When compared with the APM, the sensitivity of detection of rifampicin resistance was 85% for the NRA and 93% for the manual MGIT and the specificity was 99% and 100% respectively. Both assays, NRA (κ=0.86) and manual MGIT method (κ= 0.94) were in excellent agreement with the APM. The mean turnaround time for manual MGIT method and NRA were 08 days and 10 days respectively. Conclusion: The NRA in liquid medium and manual MGIT are useful alternatives to APM for drug susceptibility testing of M. tuberculosis in low resource settings. [ABSTRACT FROM AUTHOR]

Abstract: A rapid and accurate antimycobacterial susceptibility test is essential for effective treatment of tuberculosis. The aim of this study was to evaluate a modified method applying 2,3-diphenyl-5-thienyl-(2)-tetrazolium chloride (STC) to the Clinical and Laboratory Standards Institute (CLSI) guideline for susceptibility testing of Mycobacterium tuberculosis. A total of 132 clinical isolates of M. tuberculosis, forty-eight isolates showing resistance to one or more of the first-line antituberculosis drugs, and eighty-four fully susceptible isolates were collected from hospitals of a nationwide distribution from June to September 2004. The modified procedure was conducted basically according to the agar-proportion method described in the CLSI Guideline both with STC 50 μg/mL. The amount of growth in each well was recorded and graded at 2nd and 3rd weeks after inoculation. After 3 weeks of incubation, the diagnostic sensitivity and specificity for the detection of drug-resistant strains of STC-containing agar proportion methods were 100%, except ethambutol-low level resistance, of which the diagnostic sensitivity was 93.4%. After two weeks of incubation in STC-containing agar proportion methods, one hundred of the 107 strain–drug combinations have shown drug resistance, indicating the sensitivity of 93.5%. Especially, all 41 isoniazid-resistant strains and 19 of 21 rifampin-resistant strains (90.5%) could be detected after two weeks of incubation. A modification of the agar proportion method using STC resulted in a reliable and more easily interpretable data, and detected most of resistant strains a week earlier than conventional method. [Copyright &y& Elsevier]

Abstract: A rapid colorimetric, microplate-based nitrate reductase assay (NRA) method for antibiotic susceptibility profile of clinical isolates of Mycobacterium tuberculosis was compared with Alamar Blue assay (ABA). The results obtained by both the methods were also compared with conventional agar proportion method. The overall agreement between the results obtained by NRA and ABA was 99% and 98%, respectively, when compared with agar proportion method. Reproducible results for all the isolates were obtained within 8 days by NRA as well as ABA. The specificity of NRA method for M. tuberculosis makes it more suitable method for MIC determination. [Copyright &y& Elsevier]

As acknowledged by the Clinical and Laboratory Standards Institute (CLSI), there is an insufficient evidence base on which to recommend a standard method for antimicrobial susceptibility testing against M. ulcerans. The agar proportion method has been recognized as the standard method for susceptibility testing against Mycobacterium tuberculosis complex (MTBC) isolates for decades (Woods GL, Engenack NL, Lin G, Turnidge JD (2018) CLSI standards: guidelines for health care excellence. Susceptibility testing of mycobacteria, Nocardia spp., and other aerobic Actinomycetes, 3rd edn. Clinical and Laboratory Standards Institute Copyright©2018 Clinical and Laboratory Standards Institute, Wayne (PA)). While it is more labor-intensive and requires larger amounts of drug or compound than broth-based testing, we recommend the agar proportion method for determination of minimum inhibitory concentrations against M. ulcerans. Herewith we present the method we implemented in our laboratory over the last 2 decades., (© 2022. The Author(s), under exclusive license to Springer Science+Business Media, LLC, part of Springer Nature.)

Background: Rapid diagnosis of drug-resistant Mycobacterium tuberculosis is a challenge in low-income countries. Phenotypic drug susceptibility testing using Sensititre ® MycoTB assay and the resazurin microtitre plate assay (REMA) are relatively new innovative methods to determine drug susceptibility., Objectives: This study aimed to determine the performance of the Sensititre and REMA for M. tuberculosis drug susceptibility testing in a high-volume tuberculosis reference laboratory., Methods: A laboratory-based study was performed at the Inkosi Albert Luthuli Central Hospital Tuberculosis Laboratory from January 2014 to June 2015. The Sensititre ® MycoTB plate and REMA were compared to the gold standard agar proportion method (APM) using 134 stored isolates., Results: Agreement between the Sensititre ® MycoTB plate and APM was observed with 98% sensitivity, 82% specificity, 94% positive and 93% negative predictive values of the Sensititre ® MycoTB assay for the detection of rifampicin resistance and 97%, 96%, 99% and 88% for isoniazid resistance. Good categorical agreement between the REMA and the APM was observed among isolates with 89% sensitivity, 68% specificity, 89% positive and 68% negative predictive value for the detection of rifampicin resistance and 95%, 96%, 99% and 81% for isoniazid resistance. Results for the second-line drugs showed elevated minimum inhibitory concentrations for multidrug-resistant and extensively drug-resistant tuberculosis isolates., Conclusion: The REMA and Sensititre ® MycoTB plate are attractive alternatives to the gold standard APM for the phenotypic detection of M. tuberculosis drug resistance., Competing Interests: The authors declare that they have no financial or personal relationships that may have inappropriately influenced them in writing this article., (© 2019. The Authors.)