Antimicrobial activities of levofloxacin, clarithromycin, and KRM-1648 against Mycobacterium tuberculosis and Mycobacterium avium complex replicating within Mono Mac 6 human macrophage and A-549 type II alveolar cell lines

Preclinical Models of Nontuberculous Mycobacteria Infection for Early Drug Discovery and Vaccine Research

Nontuberculous mycobacteria (NTM) represent an increasingly prevalent etiology of soft tissue infections in animals and humans. NTM are widely distributed in the environment and while, for the most part, they behave as saprophytic organisms, in certain situations, they can be pathogenic, so much so that the incidence of NTM infections has surpassed that of Mycobacterium tuberculosis in developed countries. As a result, a growing body of the literature has focused attention on the critical role that drug susceptibility tests and infection models play in the design of appropriate therapeutic strategies against NTM diseases. This paper is an overview of the in vitro and in vivo models of NTM infection employed in the preclinical phase for early drug discovery and vaccine development. It summarizes alternative methods, not fully explored, for the characterization of anti-mycobacterial compounds.

Minimum Bactericidal Concentration Techniques in Mycobacterium tuberculosis: A Systematic Review

Minimum bactericidal concentration (MBC) assay is an accepted parameter for evaluating new antimicrobial agents, and it is frequently used as a research tool to provide a prediction of bacterial eradication. To the best of our knowledge, there is no standardization among researchers regarding the technique used to detect a drug's MBC in Mycobacterium tuberculosis. Thus, the aim of this systematic review is to discuss the available literature in determining a drug's MBC in M. tuberculosis, to find the most commonly used technique and standardize the process. A broad and rigorous literature search of three electronic databases (PubMed, Web of Knowledge, and LILACS) was performed according to the PRISMA statement. We considered studies that were published from January 1, 1990 to February 19, 2019. Google Scholar was also searched to increase the number of publications. We searched for articles using the MeSH terms "microbiological techniques," "Mycobacterium," "antibacterial agents." In addition, free terms were used in the search. The search yielded 6,674 publications. After filter application, 5,348 publications remained. Of these, we evaluated the full text of 187 publications. By applying the inclusion criteria, 69 studies were included in the present systematic review. In the literature analyzed, a great variety in the techniques used to determine a drug's MBC in M. tuberculosis was observed. The most common variability is related to the culture media used, culture incubation time, and the percentage of bacterial death for the drug to be considered as bactericidal. The most commonly used technique for drug's MBC determination was carried out using the drug's minimum inhibitory concentration (MIC) assay. Aliquots from prior MIC values were subcultured in Middlebrook agar and incubated for 4 weeks at 35°C for determining the colony forming unit (CFU) with relevance to detect 99.9% bacilli killed or reduction in 3 log₁₀ viable bacilli.

In vitro activity of collinin isolated from the leaves of Zanthoxylum schinifolium against multidrug- and extensively drug-resistant Mycobacterium tuberculosis

BACKGROUND

Tuberculosis is a very serious infectious disease that threatens humanity, and the emergence of multidrug-resistant (MDR), extensively drug-resistant (XDR) strains resistant to drugs suggests that new drug development is urgent. In order to develop new tuberculosis drug, we have conducted in vitro anti-tubercular tests on thousands of plant-derived substances and finally found collinin extracted from the leaves of Zanthoxylum schinifolium, which has an excellent anti-tuberculosis effect.

PURPOSE

To isolate an anti-tubercular bioactive compound from the leaves of Z. schinifolium and evaluate whether this agent demonstrates any potential in vitro characteristics suitable for the development of future anti-tubercular drugs to treat MDR and XDR Mycobacterium tuberculosis.

METHODS

The methanolic extracts of the leaves of Z. schinifolium were subjected to bioassay-guided fractionation against M. tuberculosis using a microbial cell viability assay. In addition, following cell cytotoxicity assay, an intracellular anti-mycobacterial activity of the most active anti-tubercular compound was investigated after it was purified.

RESULTS

The active compound with anti-tubercular activity isolated from leaves of Z. schinifolium was identified as a collinin. The extracted collinin showed anti-tubercular activity against both drug-susceptible and -resistant strains of M. tuberculosis at 50% minimum inhibitory concentrations (MIC₅₀s) of 3.13-6.25 µg/ml in culture broth and MIC₅₀s of 6.25-12.50 µg/ml inside Raw264.7 and A549 cells. Collinin had no cytotoxicity against human lung pneumocytes up to a concentration of 100 µg/ml (selectivity index > 16-32).

CONCLUSIONS

Collinin extracted from the leaves of Z. schinifolium significantly inhibits the growth of MDR and XDR M. tuberculosis in the culture broth. In addition, it also inhibits the growth of intracellular drug-susceptible and drug-resistant tuberculosis in Raw264.7 and A549 cells. To our knowledge, this is the first report on the in vitro anti-tubercular activity of collinin, and our data suggest collinin as a potential drug to treat drug-resistant tuberculosis. Further studies are warranted to assess the in vivo efficacy and therapeutic potential of collinin.

In vitro activity of alpha-viniferin isolated from the roots of Carex humilis against Mycobacterium tuberculosis

This study explores the antitubercular activity of α-viniferin, a bioactive phytochemical compound obtained from Carex humilis. α-Viniferin was active against both drug-susceptible and -resistant strains of Mycobacterium tuberculosis at MIC₅₀s of 4.6 μM in culture broth medium and MIC₅₀s of 2.3-4.6 μM inside macrophages and pneumocytes. In combination with streptomycin and ethambutol, α-viniferin exhibited an additive effect and partial synergy, respectively, against M. tuberculosis H37Rv. α-Viniferin also did not show cytotoxicity in any of the cell lines tested up to a concentration of 147 μM, which gives this compound a selectivity index of >32. Moreover, α-viniferin was active against 3 Staphylococcus species, including methicillin-susceptible Staphylococcus aureus (MSSA), methicillin-resistant Staphylococcus aureus (MRSA), and methicillin-resistant Staphylococcus epidermidis (MRSE).

Mycobacterium avium Complex Disease

Despite the ubiqitous nature of Mycobacterium avium complex (MAC) organisms in the environment, relatively few of those who are infected develop disease. Thus, some degree of susceptibility due to either underlying lung disease or immunosuppression is required. The frequency of pulmonary MAC disease is increasing in many areas, and the exact reasons are unknown. Isolation of MAC from a respiratory specimen does not necessarily mean that treatment is required, as the decision to treatment requires the synthesis of clinical, radiographic, and microbiologic information as well as a weighing of the risks and benefits for the individual patient. Successful treatment requires a multipronged approach that includes antibiotics, aggressive pulmonary hygiene, and sometimes resection of the diseased lung. A combination of azithromycin, rifampin, and ethambutol administered three times weekly is recommend for nodular bronchiectatic disease, whereas the same regimen may be used for cavitary disease but administered daily and often with inclusion of a parenteral aminoglycoside. Disseminated MAC (DMAC) is almost exclusively seen in patients with late-stage AIDS and can be treated with a macrolide in combination with ethambutol, with or without rifabutin: the most important intervention in this setting is to gain HIV control with the use of potent antiretroviral therapy. Treatment outcomes for many patients with MAC disease remain suboptimal, so new drugs and treatment regimens are greatly needed. Given the high rate of reinfection after cure, one of the greatest needs is a better understanding of where infection occurs and how this can be prevented.

Evaluation of macrolides for possible use against multidrug-resistant Mycobacterium tuberculosis

Multidrug-resistant tuberculosis (MDR-TB) is a major global health problem. The loss of susceptibility to an increasing number of drugs behoves us to consider the evaluation of non-traditional anti-tuberculosis drugs.

Clarithromycin, a macrolide antibiotic, is defined as a group 5 anti-tuberculosis drug by the World Health Organization; however, its role or efficacy in the treatment of MDR-TB is unclear. A systematic review of the literature was conducted to summarise the evidence for the activity of macrolides against MDR-TB, by evaluating in vitro, in vivo and clinical studies. PubMed and Embase were searched for English language articles up to May 2014.

Even though high minimum inhibitory concentration values are usually found, suggesting low activity against Mycobacterium tuberculosis, the potential benefits of macrolides are their accumulation in the relevant compartments and cells in the lungs, their immunomodulatory effects and their synergistic activity with other anti-TB drugs.

A future perspective may be use of more potent macrolide analogues to enhance the activity of the treatment regimen.

Cu(ii) and Co(ii) ternary complexes of quinolone antimicrobial drug enoxacin and levofloxacin: structure and biological evaluation

Four novel metal–quinolone complexes tightly binded to calf-thymus DNA and exhibited good binding propensity to albumin protein.

Evaluation of combination effects of ethanolic extract of Ziziphus mucronata Willd. subsp. mucronata Willd. and antibiotics against clinically important bacteria

A pragmatic approach to the treatment of infectious diseases with multicausal agents and prevention of the development of resistant isolates is the combination of herbal remedies with the first-line antimicrobial agents to which most of them have become resistant. This study evaluated the interactions between the ethanolic bark extract of Ziziphus mucronata with known antimicrobial agents in vitro. In this study, the results showed that varied zones of inhibitions (ZME-chloramphenicol (17-42 mm), ZME-amoxicillin (17-35 mm), ZME-tetracycline (17-36 mm), ZME-ciprofloxacin (20-41 mm), ZME-nalidixic acid (17-34 mm), and ZME-kanamycin (17-38 mm)) were produced by the antibacterial combinations. At the highest combined concentrations, 12 isolates (ZME-ciprofloxacin) > 10 isolates (ZME-chloramphenicol) = (ZME-kanamycin) > 6 isolates (ZME-amoxicillin) = (ZME-nalidixic acid) and 5 isolates (ZME-tetracycline) were inhibited with zones of inhibition greater than 20 ± 1.0 mm. Although the agar diffusion assay suggested that the interactions between the ethanolic extract of Z. mucronata and the antibiotics were both synergistic and additive in nature, the fractional inhibitory concentration indices (FICI) showed that the interactions were synergistic (54.17%), additive (27.78%), indifferent (16.67%), and antagonistic (1.39%). While the fractional inhibitory concentration indices (FICIs) for synergism ranged between 0.00391 and 0.5, that of additivity ranged between 0.516 and 1.0, indifferences ranged between 1.062 and 3.0 and antagonistic interaction was 5.0. The synergistic effects implied that the antibacterial combinations would be more effective and useful in the treatment of multicausal and multidrug-resistant bacteria than a single monotherapy of either antibacterial agent.

Rapid determination of growth inhibition of Mycobacterium tuberculosis by GC-MS/MS quantitation of tuberculostearic acid

Classical determination of growth inhibition of Mycobacterium tuberculosis in macrophages and mice by new candidate anti-TB drugs utilizes the determination of colony forming units (CFUs) from lung homogenates, a labor-intensive process requiring 2-3 weeks incubation. Qualitative analysis of tuberculostearic acid (TBSA), a cell wall associated biomarker found in M. tuberculosis, has been investigated for clinical diagnosis of tuberculosis (TB) but few reports exist of attempts to quantitate TBSA. Gas chromatography-mass spectroscopy (GC-MS/MS) was used in quantitating the derivatized methyl ester of TBSA during growth of M. tuberculosis in axenic medium, macrophage cultures and in the lungs of gamma interferon knockout (GKO) mice with and without exposure to anti-TB agents. The quantity of TBSA methyl ester (TBSAME) in the absence of and following exposure to anti-TB drugs was positively correlated with CFU in all three models. The stability of TBSA precludes its use as a surrogate for bactericidal activity but its exceptional thermal stability enables lung homogenates to be autoclaved prior to analysis. GC-MS/MS determination of TBSA is a rapid, sensitive and accurate means of detecting growth inhibition of any strain of M. tuberculosis in cell culture and in vivo.

Comprehensive treatment of extensively drug-resistant tuberculosis

BACKGROUND

Extensively drug-resistant tuberculosis has been reported in 45 countries, including countries with limited resources and a high burden of tuberculosis. We describe the management of extensively drug-resistant tuberculosis and treatment outcomes among patients who were referred for individualized outpatient therapy in Peru.

METHODS

A total of 810 patients were referred for free individualized therapy, including drug treatment, resective surgery, adverse-event management, and nutritional and psychosocial support. We tested isolates from 651 patients for extensively drug-resistant tuberculosis and developed regimens that included five or more drugs to which the infecting isolate was not resistant.

RESULTS

Of the 651 patients tested, 48 (7.4%) had extensively drug-resistant tuberculosis; the remaining 603 patients had multidrug-resistant tuberculosis. The patients with extensively drug-resistant tuberculosis had undergone more treatment than the other patients (mean [+/-SD] number of regimens, 4.2+/-1.9 vs. 3.2+/-1.6; P<0.001) and had isolates that were resistant to more drugs (number of drugs, 8.4+/-1.1 vs. 5.3+/-1.5; P<0.001). None of the patients with extensively drug-resistant tuberculosis were coinfected with the human immunodeficiency virus (HIV). Patients with extensively drug-resistant tuberculosis received daily, supervised therapy with an average of 5.3+/-1.3 drugs, including cycloserine, an injectable drug, and a fluoroquinolone. Twenty-nine of these patients (60.4%) completed treatment or were cured, as compared with 400 patients (66.3%) with multidrug-resistant tuberculosis (P=0.36).

CONCLUSIONS

Extensively drug-resistant tuberculosis can be cured in HIV-negative patients through outpatient treatment, even in those who have received multiple prior courses of therapy for tuberculosis.

Identifying putative Mycobacterium tuberculosis Rv2004c protein sequences that bind specifically to U937 macrophages and A549 epithelial cells

Virulence and immunity are still poorly understood in Mycobacterium tuberculosis. The H37Rv M. tuberculosis laboratory strain genome has been completely sequenced, and this along with proteomic technology represent powerful tools contributing toward studying the biology of target cell interaction with a facultative bacillus and designing new strategies for controlling tuberculosis. Rv2004c is a putative M. tuberculosis protein that could have specific mycobacterial functions. This study has revealed that the encoding gene is present in all mycobacterium species belonging to the M. tuberculosis complex. Rv2004c gene transcription was observed in all of this complex's strains except Mycobacterium bovis and Mycobacterium microti. Rv2004c protein expression was confirmed by using antibodies able to recognize a 54-kDa molecule by immunoblotting, and its location was detected on the M. tuberculosis surface by transmission electron microscopy, suggesting that it is a mycobacterial surface protein. Binding assays led to recognizing high activity binding peptides (HABP); five HABPs specifically bound to U937 cells, and six specifically bound to A549 cells. HABP circular dichroism suggested that they had an alpha-helical structure. HABP-target cell interaction was determined to be specific and saturable; some of them also displayed greater affinity for A549 cells than U937 cells. The critical amino acids directly involved in their interaction with U937 cells were also determined. Two probable receptor molecules were found on U937 cells and five on A549 for the two HABPs analyzed. These observations have important biological significance for studying bacillus-target cell interactions and implications for developing strategies for controlling this disease.

Characterising Mycobacterium tuberculosis Rv1510c protein and determining its sequences that specifically bind to two target cell lines

The process of Mycobacterium tuberculosis infection of the macrophage implies a very little-known initial recognition and adherence step, important for mycobacterial survival; many proteins even remain like hypothetical. The Rv1510c gene, encoding a putatively conserved membrane protein, was investigated by analysing the M. tuberculosis genome sequence data reported by Cole et al. and a previous report that used PCR assays to show that the Rv1510 gene was only present in M. tuberculosis. This article confirmed all the above and identified the transcribed gene in M. tuberculosis, Mycobacterium africanum, and in M. tuberculosis clinical isolates. Antibodies raised against peptides from this protein recognised a 44 kDa band, corresponding to Rv1510c theoretical mass (44,294 Da). Assays involving synthetic peptides covering the whole protein binding to U937 and A549 cell lines led to recognising five high activity binding peptides in the Rv1510 protein: 11094, 11095, 11105, 11108, and 11111. Their affinity constants and Hill coefficients were determined by using U937 cells. Cross-linking assays performed with some of these HABPs showed that they specifically bound to a U937 cell line 51 kDa protein, but not to Hep G2 or red blood cell proteins, showing this interaction's specificity.

Mycobacterium tuberculosis heparin-binding haemagglutinin adhesin (HBHA) triggers receptor-mediated transcytosis without altering the integrity of tight junctions

Mycobacterium tuberculosis, the etiologic agent of tuberculosis, adheres to, invades and multiplies in both professional phagocytes and epithelial cells. Adherence to epithelial cells is predominantly mediated by the 28-kDa heparin-binding haemagglutinin adhesin (HBHA), which is also required for the extrapulmonary dissemination of the bacilli. To study the cellular mechanisms that might result in HBHA-mediated extrapulmonary dissemination, we used a transwell model of cellular barrier and fluorescence microscopy and found that HBHA induces a reorganization of the actin filament network in confluent endothelial cells, but does not affect the tight junctions that link them. When coupled to colloidal gold particles, HBHA-mediated a rapid attachment of the particles to the membrane of human laryngeal epithelial cells (non polarized HEp-2 cells) and human type II pneumocytes (polarized A-549 pneumocytes). After attachment, the particles were internalized in membrane-bound vacuoles that migrated across the polarized pneumocytes to reach the basal side. Attachment of the HBHA-coated particles was not observed when the epithelial cells were pretreated with heparinase III, a lyase that specifically cleaves the heparan sulfate chains borne by the proteoglycans. Furthermore, no binding was observed when the gold particles were coated with HBHA lacking its C-terminal heparin-binding domain. These observations indicate that HBHA induces receptor-mediated endocytosis through the recognition of heparan sulfate-containing proteoglycans by the heparin-binding domain of the adhesin. In addition, the transcellular migration of the endocytic vacuoles containing HBHA-coated particles suggests that HBHA induces epithelial transcytosis, which may represent a macrophage-independent extrapulmonary dissemination mechanism leading to systemic infection by M. tuberculosis.

Fluoroquinolones and tuberculosis

Tuberculosis (TB) remains one of the main causes of morbidity worldwide, and the emergence of multi-drug resistant (MDR) Mycobacterium tuberculosis strains in some parts of the world has become a major concern. The decrease in activity of the major anti-TB drugs, such as isoniazid and rifampicin, is an important threat and alternative therapies are urgently required. The anti-TB activity of the fluoroquinolones has been under investigation since the 1980s. Many are active in vitro but only a few, including ofloxacin, ciprofloxacin, sparfloxacin, levofloxacin and lomefloxacin, have been clinically tested. Fluoroquinolones can be used in co-therapy with the available anti-TB drugs. However, the choice of fluoroquinolone should be based not only on the in vitro activity, but also on the long-term tolerance. Fluoroquinolones are novel anti-TB drugs to be used when a patient is infected with a MDR-TB strain.

Intramacrophage passage of Mycobacterium tuberculosis and M. avium complex alters the drug susceptibilities of the organisms as determined by intracellular susceptibility testing using macrophages and type II alveolar epithelial cells

Mycobacterium tuberculosis and M. avium complex strains given intramacrophage passage (I-type) were compared with those cultured in a liquid medium (E-type) for their drug susceptibilities when they were replicating in Mono-Mac-6 macrophages or A-549 cells. Their intracellular susceptibilities to rifalazil, clarithromycin, and levofloxacin were decreased more in I-type organisms than in E-type organisms, except that their rifalazil susceptibility inside A-549 cells was markedly increased in I-type organisms.