Resazurin tube method: rapid, simple, and inexpensive method for detection of drug resistance in the clinical isolates of mycobacterium tuberculosis

Insights into the in-vitro Susceptibility and Drug-Drug Interaction Profiles Against Drug-Resistant and Susceptible Mycobacterium tuberculosis Clinical Isolates in Amhara, Ethiopia

Background

In Ethiopia, tuberculosis (TB) is a major public health problem. The aim of the study was to determine the in vitro susceptibility level of drugs and drug interaction profiles against drug-resistant and susceptible M. tuberculosis clinical isolates. A laboratory-based cross-sectional study was conducted between January 2023 and August 2023. GenoType MTBDRplus v.2.0 was facilitated in genetic mutation detection. Minimum inhibitory concentration (MIC) was determined using resazurin microtitre assay (REMA), while fractional inhibitory concentration index (FICI) using resazurin drug combination microtitre assay (REDCA) for in vitro quantitative susceptibility and drug interaction prediction.

Results

Among 32 clinical isolates, a total of 14 (43.8%) RIF, 20 (62.5%) INH, 2 (6.3%) EMB-related resistant and 14 (43.8%) MDR isolates were identified. Five of RIF-resistant isolates (55.6%) carrying rpoB common mutations at codon S450L were associated with high levels of RIF-resistance with MICs of ≥ 2μg/mL, whereas 100% of isolates harboring rpoB substitutions at codons D435V and H445Y were linked with moderate or low-level RIF-resistance in the MIC ranges from 0.5 to 1μg/mL. A proportion of 81.8% of isolates harboring katG S315T mutations were associated with high-level INH resistance (MIC ≥ 1μg/mL), while the 18.2% of isolates with S315T katG mutations and 100% of isolates with inhA C-15T mutations were linked to the low-level of INH resistance with MIC variability from 0.25 to 0.5μg/mL. Our results indicated that most FICIs of the dual drugs INH+RIF and INH+LEV combination for 9 (28.1%) and 4 (12.5%) INH-resistant isolates, respectively, were ≤0.5, whereas triple drugs INH+RIF+EMB, INH+RIF+LEV and INH+EMB+LEV combination for 6 (18.8%), 11 (34.4%) and 8 (25%) INH-resistant isolates were from 0.62 to 0.75, all showed synergistic effect.

Conclusion

The study highlights that isolates with rpoB S450L and katG S315T substitutions were associated with high level of RIF and INH resistance. It is concluded that REDCA can quantitatively determine anti-mycobacterial synergy and that LEV being of potential use against INH-resistant isolates including MDR-TB when combined with RIF+INH and INH+EMB.

Rapid Diagnosis of Drug-Resistant Tuberculosis-Opportunities and Challenges

Global tuberculosis (TB) eradication is undermined by increasing prevalence of emerging resistance to available drugs, fuelling ongoing demand for more complex diagnostic and treatment strategies. Early detection of TB drug resistance coupled with therapeutic decision making guided by rapid characterisation of pre-treatment and treatment emergent resistance remains the most effective strategy for averting Drug-Resistant TB (DR-TB) transmission, reducing DR-TB associated mortality, and improving patient outcomes. Solid- and liquid-based mycobacterial culture methods remain the gold standard for Mycobacterium tuberculosis (MTB) detection and drug susceptibility testing (DST). Unfortunately, delays to result return, and associated technical challenges from requirements for specialised resource and capacity, have limited DST use and availability in many high TB burden resource-limited countries. There is increasing availability of a variety of rapid nucleic acid-based diagnostic assays with adequate sensitivity and specificity to detect gene mutations associated with resistance to one or more drugs. While a few of these assays produce comprehensive calls for resistance to several first- and second-line drugs, there is still no endorsed genotypic drug susceptibility test assay for bedaquiline, pretomanid, and delamanid. The global implementation of regimens comprising these novel drugs in the absence of rapid phenotypic drug resistance profiling has generated a new set of diagnostic challenges and heralded a return to culture-based phenotypic DST. In this review, we describe the available tools for rapid diagnosis of drug-resistant tuberculosis and discuss the associated opportunities and challenges.

Osmium-arene complexes with high potency towards Mycobacterium tuberculosis

The treatment of tuberculosis (TB) poses a major challenge as frontline therapeutic agents become increasingly ineffective with the emergence and spread of drug-resistant strains of Mycobacterium tuberculosis (Mtb). To combat this global health problem, new antitubercular agents with novel modes of action are needed. We have screened a close family of 17 organometallic half-sandwich Os(II) complexes [(arene)Os(phenyl-azo/imino-pyridine)(Cl/I)]+Y- containing various arenes (p-cymene, biphenyl, or terphenyl), and NMe2, F, Cl, or Br phenyl or pyridyl substituents, for activity towards Mtb in comparison with normal human lung cells (MRC5). In general, complexes with a monodentate iodido ligand were more potent than chlorido complexes, and the five most potent iodido complexes (MIC 1.25-2.5 µM) have an electron-donating Me2N or OH substituent on the phenyl ring. As expected, the counter anion Y (PF6-, Cl-, I-) had little effect on the activity. The pattern of potency of the complexes towards Mtb is similar to that towards human cells, perhaps because in both cases intracellular thiols are likely to be involved in their activation and their redox mechanism of action. The most active complex against Mtb is the p-cymene Os(II) NMe2-phenyl-azopyridine iodido complex (2), a relatively inert complex that also exhibits potent activity towards cancer cells. The uptake of Os from complex 2 by Mtb is rapid and peaks after 6 h, with temperature-dependence studies suggesting a major role for active transport. Significance to Metallomics Antimicrobial resistance is a global health problem. New advances are urgently needed in the discovery of new antibiotics with novel mechanisms of action. Half-sandwich organometallic complexes offer a versatile platform for drug design. We show that with an appropriate choice of the arene, an N,N-chelated ligand, and monodentate ligand, half-sandwich organo-osmium(II) complexes can exhibit potent activity towards Mycobacterium tuberculosis (Mtb), the leading cause of death from a single infectious agent. The patterns of activity of the 17 azo- and imino-pyridine complexes studied here towards Mtb and normal lung cells suggest a common redox mechanism of action involving intracellular thiols.

Non-commercial phenotypic assays for the detection of Mycobacterium tuberculosis drug resistance: a systematic review

Several rapid non-commercial culture-based methods and assays for drug susceptibility testing (DST) of Mycobacterium tuberculosis have emerged over the last decades. The aim of the current review was to summarise evidence on the performance of microscopic observation of drug susceptibility (MODS), thin-layer agar (TLA) and colorimetric redox-indicator (CRI) assays for detection of resistance to first- and second-line anti-tuberculosis (TB) drugs. Forty-three publications satisfying selection criteria were selected for data extraction. MODS and CRI assays demonstrated pooled sensitivity and specificity of > 93% for the detection of resistance to rifampicin and isoniazid and confirmed their utility for an accurate detection of multidrug-resistant TB (MDR-TB) in various settings. Sensitivity and specificity values for indirect DST for ethambutol (EMB) using CRI assays were 94.0% and 82.0%, respectively, suggesting that CRIs could be used to rule out resistance to EMB. Performance for other drugs varied more substantially across the reports. There was no sufficient evidence on the performance of the TLA assay for making any conclusion on its utility for DST. Our data suggests that non-commercial assays could be used for a rapid and accurate DST in settings where the use of commercial World Health Organization-endorsed assays could be limited due to a variety of reasons including limited resources, laboratory facilities or trained personnel. While inexpensive and easy-to-perform MODS and TLA assays can be used in low-income settings, using CRI assays for determination of minimal inhibitory concentrations may be implemented in middle- and high-income countries with high MDR-TB burden to guide clinical management of TB patients.