Three-Dimensional Rotary Culture to Model Mycobacterial Biofilms in Low-Shear Detergent-Free Liquid Suspension.

In vitro biofilm models have allowed researchers to investigate the role biofilms play in the pathogenesis, virulence, and antimicrobial drug susceptibility of a wide range of bacterial pathogens. Rotary cell culture systems create three-dimensional cellular structures, primarily applied to eukaryotic organoids, that better capture characteristics of the cells in vivo. Here, we describe how to apply a low-shear, detergent-free rotary cell culture system to generate biofilms of Mycobacterium bovis BCG. The three-dimensional biofilm model forms mycobacterial cell aggregates in suspension as surface-detached biomass, without severe nutrient starvation or environmental stress, that can be harvested for downstream experiments. Mycobacterium bovis BCG derived from cell clusters display antimicrobial drug tolerance, presence of an extracellular matrix, and evidence of cell wall remodeling, all features of biofilm-associated bacteria that may be relevant to the treatment of tuberculosis.

A Dendritic Cell-Activating Rv1876 Protein Elicits Mycobacterium Bovis BCG-Prime Effect via Th1-Immune Response.

The widely administered tuberculosis (TB) vaccine, Bacillus Calmette-Guerin (BCG), is the only licensed vaccine, but has highly variable efficiency against childhood and pulmonary TB. Therefore, the BCG prime-boost strategy is a rational solution for the development of new TB vaccines. Studies have shown that Mycobacterium tuberculosis (Mtb) culture filtrates contain proteins that have promising vaccine potential. In this study, Rv1876 bacterioferritin was identified from the culture filtrate fraction with strong immunoreactivity. Its immunobiological potential has not been reported previously. We found that recombinant Rv1876 protein induced dendritic cells' (DCs) maturation by MAPK and NF-κB signaling activation, induced a T helper type 1 cell-immune response, and expanded the population of the effector/memory T cell. Boosting BCG with Rv1876 protein enhanced the BCG-primed Th1 immune response and reduced the bacterial load in the lung compared to those of BCG alone. Thus, Rv1876 is a good target for the prime-boost strategy.

The Iron Chelator Desferrioxamine Increases the Efficacy of Bedaquiline in Primary Human Macrophages Infected with BCG.

For over 50 years, patients with drug-sensitive and drug-resistant tuberculosis have undergone long, arduous, and complex treatment processes with several antimicrobials. With the prevalence of drug-resistant strains on the rise and new therapies for tuberculosis urgently required, we assessed whether manipulating iron levels in macrophages infected with mycobacteria offered some insight into improving current antimicrobials that are used to treat drug-resistant tuberculosis. We investigated if the iron chelator, desferrioxamine, can support the function of human macrophages treated with an array of second-line antimicrobials, including moxifloxacin, bedaquiline, amikacin, clofazimine, linezolid and cycloserine. Primary human monocyte-derived macrophages were infected with Bacillus Calmette-Guérin (BCG), which is pyrazinamide-resistant, and concomitantly treated for 5 days with desferrioxamine in combination with each one of the second-line tuberculosis antimicrobials. Our data indicate that desferrioxamine used as an adjunctive treatment to bedaquiline significantly reduced the bacterial load in human macrophages infected with BCG. Our findings also reveal a link between enhanced bactericidal activity and increases in specific cytokines, as the addition of desferrioxamine increased levels of IFN-γ, IL-6, and IL-1ß in BCG-infected human monocyte-derived macrophages (hMDMs) treated with bedaquiline. These results provide insight, and an in vitro proof-of-concept, that iron chelators may prove an effective adjunctive therapy in combination with current tuberculosis antimicrobials.

Recombinant ArgF PLGA nanoparticles enhances BCG induced immune responses against Mycobacterium bovis infection.

Mycobacterium bovis (M. bovis) is a member of mycobacterium tuberculosis complex (MTBC), and a causative agent of chronic respiratory disease in a wide range of hosts. Bacillus Calmette-Guerin (BCG) vaccine is mostly used for the prevention of childhood tuberculosis. Further substantial implications are required for the development and evaluation of new tuberculosis (TB) vaccines as well as improving the role of BCG in TB control strategies. In this study, we prepared PLGA nanoparticles encapsulated with argF antigen (argF-NPs). We hypothesized, that argF nanoparticles mediate immune responses of BCG vaccine in mice models of M. bovis infection. We observed that mice vaccinated with argF-NPs exhibited a significant increase in secretory IFN-γ, CD4+ T cells response and mucosal secretory IgA against M. bovis infection. In addition, a marked increase was observed in the level of secretory IL-1ß, TNF-α and IL-10 both in vitro and in vivo upon argF-NPs vaccination. Furthermore, argF-NPs vaccination resulted in a significant reduction in the inflammatory lesions in the lung's tissues, minimized the losses in total body weight and reduced M. bovis burden in infected mice. Our results indicate that BCG prime-boost strategy might be a promising measure for the prevention against M. bovis infection by induction of CD4+ T cells responses and mucosal antibodies.

Natural resistance to worms exacerbates bovine tuberculosis severity independently of worm coinfection.

Pathogen interactions arising during coinfection can exacerbate disease severity, for example when the immune response mounted against one pathogen negatively affects defense of another. It is also possible that host immune responses to a pathogen, shaped by historical evolutionary interactions between host and pathogen, may modify host immune defenses in ways that have repercussions for other pathogens. In this case, negative interactions between two pathogens could emerge even in the absence of concurrent infection. Parasitic worms and tuberculosis (TB) are involved in one of the most geographically extensive of pathogen interactions, and during coinfection worms can exacerbate TB disease outcomes. Here, we show that in a wild mammal natural resistance to worms affects bovine tuberculosis (BTB) severity independently of active worm infection. We found that worm-resistant individuals were more likely to die of BTB than were nonresistant individuals, and their disease progressed more quickly. Anthelmintic treatment moderated, but did not eliminate, the resistance effect, and the effects of resistance and treatment were opposite and additive, with untreated, resistant individuals experiencing the highest mortality. Furthermore, resistance and anthelmintic treatment had nonoverlapping effects on BTB pathology. The effects of resistance manifested in the lungs (the primary site of BTB infection), while the effects of treatment manifested almost entirely in the lymph nodes (the site of disseminated disease), suggesting that resistance and active worm infection affect BTB progression via distinct mechanisms. Our findings reveal that interactions between pathogens can occur as a consequence of processes arising on very different timescales.

3D QSAR studies on amphiphilic indoles for antimycobacterial activity.

A persistent infection prolongs treatment duration and also enhances the chance of resistance development against antibiotics. Recently, a class of amphiphilic indole derivatives was discovered exhibiting bactericidal activity against both growing and nongrowing Mycobacterium bovis BCG (M. bovis BCG). These antibacterials are suggested to disturb the integrity and functioning of the cell membrane, a property that can help eradicate persistent organisms. This study article describes field-based three-dimensional quantitative structure-activity relationship (3D-QSAR) studies of 79 amphiphilic indole derivatives. The aim of this QSAR study is to optimize this class of compounds for the development of more potent antimycobacterial agents. The results obtained indicate that steric interactions are crucial for antimycobacterial activity, while hydrogen bond donor groups participate negligibly in activity. The derived 3D-QSAR models showed acceptable r2 (0.91) and q2 (0.91) with a root mean squared error (RMSE) of 0.08. The models were cross-validated using the leave-one-out method. Applying the same QSAR model to another congeneric series of amphiphilic indoles externally validated the QSAR model. The model could appreciably predict the activity (pMIC50 ) of this congeneric series of amphiphilic indoles, with an RMSE of 0.49, indicating the robustness of the model and its efficiency in predicting the potentially active compounds.

GPR183 Regulates Interferons, Autophagy, and Bacterial Growth During Mycobacterium tuberculosis Infection and Is Associated With TB Disease Severity.

Oxidized cholesterols have emerged as important signaling molecules of immune function, but little is known about the role of these oxysterols during mycobacterial infections. We found that expression of the oxysterol-receptor GPR183 was reduced in blood from patients with tuberculosis (TB) and type 2 diabetes (T2D) compared to TB patients without T2D and was associated with TB disease severity on chest x-ray. GPR183 activation by 7α,25-dihydroxycholesterol (7α,25-OHC) reduced growth of Mycobacterium tuberculosis (Mtb) and Mycobacterium bovis BCG in primary human monocytes, an effect abrogated by the GPR183 antagonist GSK682753. Growth inhibition was associated with reduced IFN-ß and IL-10 expression and enhanced autophagy. Mice lacking GPR183 had significantly increased lung Mtb burden and dysregulated IFNs during early infection. Together, our data demonstrate that GPR183 is an important regulator of intracellular mycobacterial growth and interferons during mycobacterial infection.

The In Vitro M1/M2 Polarization of Macrophages of BCG-Infected Mice.

Cultured peritoneal macrophages from intact (control) and BCG-infected (experiment) male BALB/c mice were studied 90 days after infection. Polarization of macrophages by M1 (expression of GM-CSF, IFNγ, and CD16/32) and M2 (expression of bFGF and CD36) differentiation pathways was studied with consideration for their the nuclearity class. Mononuclear cells predominated (90% and higher) in macrophage cultures of both groups and presumably, were presented by mainly epithelioid cells. The results indicated polarization of mononuclear and multinuclear macrophages in the M2 direction under conditions of BCG granulomatosis and a higher initial M2 polarization of binuclear macrophages. In control cultures, the ratio of M2 to M1 macrophages was 0.57, in experimental cultures this ratio was 1.6. It seems that long persistence of Mycobacterium tuberculosis in macrophages served as a factor stimulating the plastic processes and transformation of macrophages into epithelioid cells that form the "core" of granulomas and their enlargement upon incorporation of macrophages.

The mycolic acid reductase Rv2509 has distinct structural motifs and is essential for growth in slow-growing mycobacteria.

The final step in mycolic acid biosynthesis in Mycobacterium tuberculosis is catalysed by mycolyl reductase encoded by the Rv2509 gene. Sequence analysis and homology modelling indicate that Rv2509 belongs to the short-chain fatty acid dehydrogenase/reductase (SDR) family, but with some distinct features that warrant its classification as belonging to a novel family of short-chain dehydrogenases. In particular, the predicted structure revealed a unique α-helical C-terminal region which we demonstrated to be essential for Rv2509 function, though this region did not seem to play any role in protein stabilisation or oligomerisation. We also show that unlike the M. smegmatis homologue which was not essential for growth, Rv2509 was an essential gene in slow-growing mycobacteria. A knockdown strain of the BCG2529 gene, the Rv2509 homologue in Mycobacterium bovis BCG, was unable to grow following the conditional depletion of BCG2529. This conditional depletion also led to a reduction of mature mycolic acid production and accumulation of intermediates derived from 3-oxo-mycolate precursors. Our studies demonstrate novel features of the mycolyl reductase Rv2509 and outline its role in mycobacterial growth, highlighting its potential as a new target for therapies.

Longitudinal dynamics of herd-level Mycobacterium bovis MLVA type surveillance in cattle in Northern Ireland 2003-2016.

Investigating genetically-structured diversity in pathogen populations over time is important to better understand disease maintenance and spread. Herd-level surveillance of Mycobacterium bovis genotypes (multi-locus VNTR analysis types, MLVA types) from all culture-confirmed bovine tuberculosis (TB) herd cases was undertaken in Northern Ireland (NI), generating an unparalleled, longitudinal, population-level 14-year survey for this pathogen. Across this population, 295 genetically-distinct M. bovis MLVA types were identified in the 19,717 M. bovis isolates surveyed. Of these, the most frequent was MLVA type 002 (23.0%); 151 MLVA types were represented more than once, in groups ranging from 2 to 4438 isolates. Only 23 MLVA types were isolated in all 14 years. Investigating inter-annual frequency of M. bovis MLVA types, examples of statistically-significant expansions (MLVA types 002, 004, 006, 009 and 027), contractions (MLVA types 001, 007 and 011) and maintenance (MLVA types 003 and 005) were disclosed, during a period of fluctuating bovine TB herd-level incidence at the NI scale. The fixed period frequency distribution of MLVA types remained highly right-skewed. Novel VNTR copy number variant MLVA types (N = 242; an average of 17 per annum) were identified throughout the survey. The MLVA type distribution in the landscape was not random; MLVA types showed statistically-significant geographical localization and strong spatial associations with Divisional Veterinary Office (DVO) regions. There was also evidence of differential risk of particular MLVA types across breeds (Holstein/Friesian vs. other), age-class, and sex and some evidence of an association between the number of animals testing positive for bovine TB during the disclosing test and particular MLVA types, although there was substantial variation.

WQ-3810: A new fluoroquinolone with a high potential against fluoroquinolone-resistant Mycobacterium tuberculosis.

Fluoroquinolone (FQ) resistance in Mycobacterium tuberculosis (Mtb), caused by amino acid substitutions in DNA gyrase, has been increasingly reported worldwide. WQ-3810 is a newly developed FQ that is highly active against FQ-resistant pathogens; however, its activity against Mtb has not been evaluated. Herein we examined the efficacy of WQ-3810 against Mtb through the use of recombinant Mtb DNA gyrases. In addition, in vitro antimycobacterial activity of WQ-3810 was evaluated against recombinant Mtb var. bovis Bacille Calmette-Guérin strains in which gyrase-coding genes were replaced with Mtb variants containing resistance-conferring mutations. WQ-3810 showed a higher inhibitory activity than levofloxacin against most recombinant DNA gyrases with FQ-resistance mutations. Furthermore, WQ-3810 showed inhibition even against a DNA gyrase variant harboring a G88C mutation which is thought to confer the highest resistance against FQs in clinical Mtb isolates. In contrast, the FQ susceptibility test showed that WQ-3810 had relatively weak mycobactericidal activity compared with moxifloxacin. However, the combination of WQ-3810 and ethambutol showed the greatest degree of synergistic activity against recombinant strains. Since FQs and ethambutol have been used in multi-drug therapy for tuberculosis, WQ-3810 might represent a new, potent anti-tuberculosis drug that can be effective even against FQ-resistant Mtb strains.

Amphiphilic Polymethyloxazoline-Polyethyleneimine Copolymers: Interaction with Lipid Bilayer and Antibacterial Properties.

Polycations, mimicking activity of antibacterial peptides, belong to an important class of molecules investigated as a support or as an alternative to antibiotics. In this work, studies of modified linear amphiphilic statistical polymethyloxazoline (PMOX) and polyethyleneimine copolymers (PMOX_PEI) series are presented. Variation of PEI content in the structure results in controllable changes of polymeric aggregates zeta potential. The structure with the highest positive charge shows the best antimicrobial activity, well visible in tests against model Gram-positive and Gram-negative bacteria, fungi, and mycobacterium strains. The polymer toxicity is evaluated with MTT and hemolysis assay as a reference. Quartz crystal microbalance (QCM-D) is used to investigate interaction between polycations and a model lipid membrane. Polymer activity correlates well with molecular structure, showing that amphiphilic component is altering polymer behavior in contact with the lipid bilayer.

Cyclipostins and Cyclophostin Analogues as Multitarget Inhibitors That Impair Growth of Mycobacterium abscessus.

Twelve new Cyclophostin and Cyclipostins analogues (CyC19-30) were synthesized, thus extending our series to 38 CyCs. Their antibacterial activities were evaluated against four pathogenic mycobacteria (Mycobacterium abscessus, Mycobacterium marinum, Mycobacterium bovis BCG, and Mycobacterium tuberculosis) and two Gram negative bacteria. The CyCs displayed very low toxicity toward host cells and were only active against mycobacteria. Importantly, several CyCs were active against extracellular M. abscessus (CyC17/CyC18ß/CyC25/CyC26) or intramacrophage residing mycobacteria (CyC7(α,ß)/CyC8(α,ß)) with minimal inhibitory concentrations (MIC50) values comparable to or better than those of amikacin or imipenem, respectively. An activity-based protein profiling combined with mass spectrometry allowed identification of the potential target enzymes of CyC17/CyC26, mostly being involved in lipid metabolism and/or in cell wall biosynthesis. Overall, these results strengthen the selective activity of the CyCs against mycobacteria, including the most drug-resistant M. abscessus, through the cumulative inhibition of a large number of Ser- and Cys-enzymes participating in key physiological processes.

NU-6027 Inhibits Growth of Mycobacterium tuberculosis by Targeting Protein Kinase D and Protein Kinase G.

Tuberculosis (TB) is a global health concern, and this situation has further worsened due to the emergence of drug-resistant strains and the failure of BCG vaccine to impart protection. There is an imperative need to develop highly sensitive, specific diagnostic tools, novel therapeutics, and vaccines for the eradication of TB. In the present study, a chemical screen of a pharmacologically active compound library was performed to identify antimycobacterial compounds. The phenotypic screen identified a few novel small-molecule inhibitors, including NU-6027, a known CDK-2 inhibitor. We demonstrate that NU-6027 inhibits Mycobacterium bovis BCG growth in vitro and also displayed cross-reactivity with Mycobacterium tuberculosis protein kinase D (PknD) and protein kinase G (PknG). Comparative structural and sequence analysis along with docking simulation suggest that the unique binding site stereochemistry of PknG and PknD accommodates NU-6027 more favorably than other M. tuberculosis Ser/Thr protein kinases. Further, we also show that NU-6027 treatment induces the expression of proapoptotic genes in macrophages. Finally, we demonstrate that NU-6027 inhibits M. tuberculosis growth in both macrophage and mouse tissues. Taken together, these results indicate that NU-6027 can be optimized further for the development of antimycobacterial agents.

A mycobacteriophage genomics approach to identify novel mycobacteriophage proteins with mycobactericidal properties.

Mycobacteriophages that are specific to mycobacteria are sources of various effector proteins that are capable of eliciting bactericidal responses. We describe a genomics approach in combination with bioinformatics to identify mycobacteriophage proteins that are toxic to mycobacteria upon expression. A genomic library comprising phage genome collections was screened for clones capable of killing Mycobacterium smegmatis strain mc2155. We identified four unique clones: clones 45 and 12N (from the mycobacteriophage D29) and clones 66 and 85 (from the mycobacteriophage Che12). The gene products from clones 66 and 45 were identified as Gp49 of the Che12 phage and Gp34 of the D29 phage, respectively. The gene products of the other two clones, 85 and 12N, utilized novel open reading frames (ORFs) coding for synthetic proteins. These four clones (clones 45, 66, 85 and 12N) caused growth defects in M. smegmatis and Mycobacterium bovis upon expression. Clones with Gp49 and Gp34 also induced growth defects in Escherichia coli, indicating that they target conserved host machineries. Their expression induced various morphological changes, indicating that they affected DNA replication and cell division steps. We predicted that Gp34 is a Xis protein that is required in phage DNA excision from the bacterial chromosome. Gp49 is predicted to have an HTH motif with DNA-bending/twisting properties. We suggest that this methodology is useful to identify new phage proteins with the desired properties without laboriously characterizing the individual phages. It is universal and could be applied to other bacteria-phage systems. We speculate that the existence of a virtually unlimited number of phages with unique gene products could offer a cheaper and less hazardous alternative to explore new antimicrobial molecules.

The prominent alteration in transcriptome and metabolome of Mycobacterium bovis BCG str. Tokyo 172 induced by vitamin B1.

BACKGROUND: Vitamin B1 (VB1) is a crucial dietary nutrient and essential cofactor for several key enzymes in the regulation of cellular and metabolic processes, and more importantly in the activation of immune system. To date, the precise role of VB1 in Mycobacterium tuberculosis remains to be fully understood. RESULTS: In this study, the transcriptional and metabolic profiles of VB1-treated Mycobacterium. bovis BCG were analyzed by RNA-sequencing and LC-MS (Liquid chromatography coupled to mass spectrometry). The selection of BCG strain was based on its common physiological features shared with M. tuberculosis. The results of cell growth assays demonstrated that VB1 inhibited the BCG growth rate in vitro. Transcriptomic analysis revealed that the expression levels of genes related to fatty acid metabolism, cholesterol metabolism, glycolipid catabolism, DNA replication, protein translation, cell division and cell wall formation were significantly downregulated in M. bovis BCG treated with VB1. In addition, the metabolomics LC-MS data indicated that most of the amino acids and adenosine diphosphate (ADP) were decreased in M. bovis BCG strain after VB1 treatment. CONCLUSIONS: This study provides the molecular and metabolic bases to understand the impacts of VB1 on M.bovis BCG.

Traditional detoxification of Jatropha curcas L. seeds.

ETHNOPHARMACOLOGICAL RELEVANCE: Jatropha curcas L. is a plant with high cultural significance for quilombola communities of Oriximiná (Pará State, Brazil). Although the plant is highly toxic, its seeds are used in these communities to treat tuberculosis and related diseases and symptoms. AIM OF THE STUDY: This study was designed to provide a scientific rationale for the traditional detoxification method and use of J. curcas seeds in quilombola communities of Oriximiná. MATERIALS AND METHODS: J. curcas seeds were manually separated into testa, tegmen, endosperm, and embryo, and then methanolic extracts of each sample were prepared. The traditional preparation of J. curcas seeds consists of a water extract of endosperms that is known as "milk of pinhão-branco". The content of phorbol esters (PEs) in the extracts was analyzed by High-Performance Liquid Chromatography with Diode-Array Detection (HPLC-DAD). The cytotoxic activity was evaluated in human monocytic cell line THP-1 by Resazurin Reduction Assay, and antimycobacterial activity was assessed by determining Minimal Inhibitory Concentration (MIC) values against H37Rv and BCG strains using the Resazurin Microtiter Assay (REMA). RESULTS: The content analysis revealed that the distribution of PEs within the seeds is not homogeneous. High contents were found in tegmens (4.22 ±â€¯0.25-15.52 ±â€¯0.06 mg/g) and endosperms (1.61 ±â€¯0.07-5.00 ±â€¯0.42 mg/g), while concentrations found in testas and embryos were all below 0.5 mg/g. The traditional preparation derived from the endosperm of J. curcas contained significantly less PEs than the endosperms (0.01 ±â€¯0.005 mg/g). Against THP-1 cells, all the parts of the seed showed cytotoxic activity, while the traditional preparation was considered non-cytotoxic. Nevertheless, only the tegmen and endosperm of J. curcas were considered active against M. tuberculosis and M. bovis (MIC = 200 µg/mL). CONCLUSION: The results of this study indicated that the traditional processing performed by the quilombola people from Oriximiná is effective in reducing the toxicity of J. curcas seeds. Although inactive against mycobacteria, the extensive use of the traditional preparation and its low toxicity encourage further studies to investigate other biological activities.

Modeling Host-Pathogen Interaction to Elucidate the Metabolic Drug Response of Intracellular Mycobacterium tuberculosis.

Little is known about the metabolic state of Mycobacterium tuberculosis (Mtb) inside the phagosome, a compartment inside phagocytes for killing pathogens and other foreign substances. We have developed a combined model of Mtb and human metabolism, sMtb-RECON and used this model to predict the metabolic state of Mtb during infection of the host. Amino acids are predicted to be used for energy production as well as biomass formation. Subsequently we assessed the effect of increasing dosages of drugs targeting metabolism on the metabolic state of the pathogen and predict resulting metabolic adaptations and flux rerouting through various pathways. In particular, the TCA cycle becomes more important upon drug application, as well as alanine, aspartate, glutamate, proline, arginine and porphyrin metabolism, while glycine, serine, and threonine metabolism become less important. We modeled the effect of 11 metabolically active drugs. Notably, the effect of eight could be recreated and two major profiles of the metabolic state were predicted. The profiles of the metabolic states of Mtb affected by the drugs BTZ043, cycloserine and its derivative terizidone, ethambutol, ethionamide, propionamide, and isoniazid were very similar, while TMC207 is predicted to have quite a different effect on metabolism as it inhibits ATP synthase and therefore indirectly interferes with a multitude of metabolic pathways.

Repurposing artemisinin as an anti-mycobacterial agent in synergy with rifampicin.

The current anti-TB treatment consists of a prolonged multi-drug therapy. Interventional strategies are required to reduce the chemotherapeutic load. In this regard, we have previously identified a synergistic interaction between hydroperoxides and rifampicin. This strategy has been extended here to repurpose a new drug against TB. A hydrophobic antimalarial drug, artemisinin, with an unstable endoperoxide bridge structure, has been investigated as a potential candidate. In combination with rifampicin, artemisinin was found to be synergistic against M. bovis BCG and M. tuberculosis H37Ra. Furthermore, artemisinin was observed to induce peroxides in a time and concentration dependent manner and the levels of the peroxides were significantly higher in cells treated with the drug pair. Coupled with rapid disintegration of the membrane, this enhanced the clearance of the bacterial culture in vitro. On the other hand, formation of the peroxides was significantly reduced in the presence of ascorbic acid, an antioxidant. This translated to a loss of the synergistic effect of the combination, indicating the importance of peroxide formation in the mode of action of artemisinin. Interestingly, artemisinin also had a synergistic interaction with isoniazid, amikacin and ethambutol and an additive interaction with moxifloxacin, other drugs commonly used against TB.