Search

Mycobacterium tuberculosis DNA gyrase manipulates the DNA topology using controlled breakage and religation of DNA driven by ATP hydrolysis. DNA gyrase has been validated as the enzyme target of fluoroquinolones (FQs), second-line antibiotics used for the treatment of multidrug-resistant tuberculosis. Mutations around the DNA gyrase DNA-binding site result in the emergence of FQ resistance in M. tuberculosis; inhibition of DNA gyrase ATPase activity is one strategy to overcome this. Here, virtual screening, subsequently validated by biological assays, was applied to select candidate inhibitors of the M. tuberculosis DNA gyrase ATPase activity from the Specs compound library (www.specs.net). Thirty compounds were identified and selected as hits for in vitro biological assays, of which two compounds, G24 and G26, inhibited the growth of M. tuberculosis H37Rv with a minimal inhibitory concentration of 12.5 μg/mL. The two compounds inhibited DNA gyrase ATPase activity with IC50 values of 2.69 and 2.46 μM, respectively, suggesting this to be the likely basis of their antitubercular activity. Models of complexes of compounds G24 and G26 bound to the M. tuberculosis DNA gyrase ATP-binding site, generated by molecular dynamics simulations followed by pharmacophore mapping analysis, showed hydrophobic interactions of inhibitor hydrophobic headgroups and electrostatic and hydrogen bond interactions of the polar tails, which are likely to be important for their inhibition. Decreasing compound lipophilicity by increasing the polarity of these tails then presents a likely route to improving the solubility and activity. Thus, compounds G24 and G26 provide attractive starting templates for the optimization of antitubercular agents that act by targeting DNA gyrase.

Isoxazoline derivatives of the natural products eugenol, 1’- S-acetoxychavicol acetate and sclareol are prepared through 1,3-dipolar cycloaddition reactions in an aqueous buffered system. The compounds are evaluated for their antitubercular and antibacterial activities. Compounds 2, 2a and 3f display strong antitubercular activity with minimum inhibitory concentration values of 26.68, 17.89 and 14.58 µM, respectively. Furthermore, derivative 3f exhibits antibacterial activity against Bacillus cereus (minimum inhibitory concentration value of 29.16 µM). Isoxazoline derivatives of 1’- S-acetoxychavicol acetate demonstrate improvements in cytotoxicity, and derivative 3f of sclareol demonstrates improved antitubercular and antibacterial activities. Isoxazolines derived from natural products exhibit Mycobacterium tuberculosis enoyl-acyl carrier protein reductase (InhA) inhibitory activity, and molecular modelling predicts that they form hydrogen bonding and hydrophobic interactions with NADH and with the key residues of the InhA binding site.

New ciprofloxacin/ quaternary ammonium salts 3a–e were designed and synthesized as potential antimicrobial agents. Most of the prepared derivatives showed promising dual antibacterial/antifungal activities. Compound 3e was the most potent and afforded vast spectrum antibacterial activity against S. aureus and most of the tested Gram-negative bacterial strains with MIC values ranging from 1.53–9.54 µg/mL. Moreover, ciprofloxacin and compound 3e induced DNA cleavage in S. aureus DNA gyrase and S. aureus TOPO IV DNA by 1 and 10 µM, respectively. In addition, docking study results agreed with results of DNA cleavage assays where all the tested compounds showed no additional significant interactions over the parent ciprofloxacin. On the other side, compounds 3e and 3f exhibited outstanding antifungal activity better than the reference itraconazole with MICs of 1.87, 4.67, and 11.22 µg/mL, respectively, against Candida. albicans. These data suggest the prevalence of another mechanism in addition to DNA gyrase circumvention, like metal chelation, antibiofilm, and/or improvement of lipophilicity and subsequent penetration.

The enoyl-acyl carrier protein reductase InhA of Mycobacterium tuberculosis is an attractive, validated target for antituberculosis drug development. Moreover, direct inhibitors of InhA remain effective against InhA variants with mutations associated with isoniazid resistance, offering the potential for activity against MDR isolates. Here, structure-based virtual screening supported by biological assays was applied to identify novel InhA inhibitors as potential antituberculosis agents. High-speed Glide SP docking was initially performed against two conformations of InhA differing in the orientation of the active site Tyr158. The resulting hits were filtered for drug-likeness based on Lipinski’s rule and avoidance of PAINS-like properties and finally subjected to Glide XP docking to improve accuracy. Sixteen compounds were identified and selected for in vitro biological assays, of which two (compounds 1 and 7) showed MIC of 12.5 and 25 μg/mL against M. tuberculosis H37Rv, respectively. Inhibition assays against purified recombinant InhA determined IC50 values for these compounds of 0.38 and 0.22 μM, respectively. A crystal structure of the most potent compound, compound 7, bound to InhA revealed the inhibitor to occupy a hydrophobic pocket implicated in binding the aliphatic portions of InhA substrates but distant from the NADH cofactor, i.e., in a site distinct from those occupied by the great majority of known InhA inhibitors. This compound provides an attractive starting template for ligand optimization aimed at discovery of new and effective compounds against M. tuberculosis that act by targeting InhA.

The aim of this article was to develop a three-layer mask, which was made of a polypropylene filter containing mangosteen extract by spray-coating technique in order to enhance antibacterial and antituberculosis activities. The bacterial filtration efficiency was performed by spraying the biological aerosol through the filters. Breathability of face masks was also measured as a pressure drop parameters. The physical properties of filters were evaluated in terms of surface morphology and water contact angle. The coated filters were then challenged with multidrug-resistant tuberculosis, Staphylococcus aureus and Escherichia coli as the representative bacteria. The results showed that the increase in the mangosteen extract concentration for coating caused fiber diameter, hydrophilicity, % BFE (> 95%) and pressure drop of filters to be also increased. Investigation into release characteristic of mangosteen extract-coated polypropylene filters exhibited initial burst release after 60 min of immersion in a phosphate buffer solution. The coated filter exhibited good antibacterial performances against three types of pathogens. An in vitro cytotoxic test showed that 2% and 5% w/v mangosteen extract-coated polypropylene filters were not toxic by an indirect cytotoxicity test using L929 mouse fibroblast cells. This study demonstrated that the filters coated with mangosteen extract significantly play an important role in achieving antibacterial face mask.

Various classes of natural products and synthetic compounds were tested against reference strains and clinical multidrug resistant isolates of Mycobacterium tuberculosis. Vermelhotin (19), a natural tetramic acid from fungi, was the most active toward clinical MDR TB isolates (MIC 1.5-12.5 μg/mL). Synthetic compounds (i.e. benzoxazocines, coumarins, chromenes, and pyrrolodiquinoline derivatives) were prepared by green chemistry approaches. Under microwave irradiation, a one-pot synthesis of pyrrolodiquinoline 85 was achieved by homocoupling of 1-methylquinolinium iodide; the structure of 85 was confirmed by single-crystal X-ray analysis. Compound 85 and its derivative 86 exhibited potent anti-tubercular activity (MIC 0.3-6.2 μg/mL) against clinical MDR TB isolates, and they displayed weak cytotoxicity toward normal cell line. The scaffold of 85 and 86 is potential for antimycobacterial activity.

A new series of mangostin analogs of natural α-mangostin from mangosteen was prepared and their antimycobacterial activity was evaluated in vitro against Mycobacterium tuberculosis H(37)Ra. The results showed that the monoalkyl tetrahydro α-mangostin analogs displayed increased antimycobacterial activity as compared with the lead natural xanthone, α-mangostin. Among the tested compounds, 6-methoxytetrahydro α-mangostin (16) exhibited the most potent antimycobacterial activity with minimum inhibitory concentration (MIC) of 0.78 µg/mL. The activity of the monoalkylated and monoacylated tetrahydro α-mangostins decreases as the length of carbon chain increases. The methyl ether analog was also active against the multidrug-resistant (MDR) strains with pronounced MICs of 0.78-1.56 µg/mL.

In the process of evaluating the effect of several plant extracts against Mycobacterium tuberculosis using the Microplate Alamar Blue Assay (MABA), an extract of Thai herb Alpinia galanga rhizome and its major component, 1′-acetoxychavicol acetate (ACA), exhibited marked anti-tuberculosis activity. The minimal inhibition concentrations (MICs) of the S-enantiomer of ACA (S-ACA) against M. tuberculosis H37Ra ATCC 25177 and H37Rv ATCC 27294 strains were 0.2 µg/mL and 0.7 µg/mL, respectively. More than 95% of 100 drug-sensitive and 50 drug-resistant mycobacterial clinical isolates were inhibited by extracted S-ACA at 1.0 µg/mL. All of the remaining isolates were inhibited at 2.0 µg/mL. In contrast to the S-enantiomer, synthetic racemic 1′-R,S-ACA (rac-ACA) showed MICs of 0.5 µg/mL and 2.7 µg/mL for M. tuberculosis H37Ra ATCC 25177 and H37Rv ATCC 27294, respectively, suggesting that the anti-tuberculosis effect might be primarily due to the S-form. These observations were in line with the MICs of rac-ACA against 98% of 93 drug-resistant clinical isolates, which showed the effective inhibitory dose at 2.0 µg/mL. After exposure to 2.7 µg/mL of rac-ACA for at least 3 h, the tubercle bacilli were completely killed. These demonstrated that ACA had potent anti-TB activity.

A new fluorescence in situ hybridization assay based on peptide nucleic acid probes (MTB and NTM probes targeting tuberculous and nontuberculous species, respectively) for the identification of Mycobacterium tuberculosis complex and differentiation between tuberculous and nontuberculous mycobacteria (NTM) was evaluated using Lowenstein-Jensen (LJ) solid cultures from 100 consecutive sputum samples and 50 acid-fast bacillus (AFB)-positive sputum samples as well as Mycobacteria Growth Indicator Tube (MGIT) liquid cultures from 80 AFB-positive sputum samples. Mycobacterium species could be identified from a total of 53 LJ cultures and 77 MGIT cultures. The diagnostic specificities of the MTB and NTM probes were 100% for both cultures. The diagnostic sensitivities of the MTB probe for the LJ and MGIT cultures were 98 and 99%, respectively, whereas the sensitivities of the NTM probe were 57 and 100%, respectively. The relatively low sensitivity of the NTM probe was due to a high proportion of M. fortuitum , which is not identified by the probe.

TB PNA FISH is a new fluorescence in situ hybridization (FISH) method using peptide nucleic acid (PNA) probes for differentiation between species of the Mycobacterium tuberculosis complex (MTC) and nontuberculous mycobacteria (NTM) in acid-fast bacillus-positive (AFB+) cultures is described. The test is based on fluorescein-labelled PNA probes that target the rRNA of MTC or NTM species applied to smears of AFB+ cultures for microscopic examination. Parallel testing with the two probes serves as an internal control for each sample such that a valid test result is based on one positive and one negative reaction. TB PNA FISH was evaluated with 30 AFB+ cultures from Denmark and 42 AFB+ cultures from Thailand. The MTC-specific PNA probe showed diagnostic sensitivities of 84 and 97%, respectively, and a diagnostic specificity of 100% in both studies, whereas the NTM-specific PNA probe showed diagnostic sensitivities of 91 and 64%, respectively, and a diagnostic specificity of 100% in both studies. The low sensitivity of the NTM-specific PNA probe in the Thai study was due to a relatively high prevalence of Mycobacterium fortuitum , which is not identified by the probe. In total, 63 (87%) of the cultures were correctly identified as MTC ( n = 46) or NTM ( n = 17), whereas the remaining 9 were negative with both probes and thus the results were inconclusive. None of the samples were incorrectly identified as MTC or NTM; thus, the predictive value of a valid test result obtained with TB PNA FISH was 100%.

Tetrahydro α-mangostin analogues of natural α-mangostin are prepared and their antimycobacterial activities are evaluated in vitro.

A new series of mangostin analogs of natural α-mangostin from mangosteen was prepared and their antimycobacterial activity was evaluated in vitro against Mycobacterium tuberculosis H(37)Ra. The results showed that the monoalkyl tetrahydro α-mangostin analogs displayed increased antimycobacterial activity as compared with the lead natural xanthone, α-mangostin. Among the tested compounds, 6-methoxytetrahydro α-mangostin (16) exhibited the most potent antimycobacterial activity with minimum inhibitory concentration (MIC) of 0.78 µg/mL. The activity of the monoalkylated and monoacylated tetrahydro α-mangostins decreases as the length of carbon chain increases. The methyl ether analog was also active against the multidrug-resistant (MDR) strains with pronounced MICs of 0.78-1.56 µg/mL.

Bisbenzylisoquinoline alkaloids, tiliacorinine (1), 2'-nortiliacorinine (2), and tiliacorine (3), isolated from the edible plant, Tiliacora triandra, as well as a synthetic derivative, 13'-bromo-tiliacorinine (4), were tested against 59 clinical isolates of multidrug-resistant Mycobacterium tuberculosis (MDR-MTB). The alkaloids 1-4 showed MIC values ranging from 0.7 to 6.2 μg/ml, but they exhibited the MIC value at 3.1 μg/ml against most MDR-MTB isolates. The present work suggests that bisbenzylisoquinoline alkaloids are potential new chemical scaffolds for antimycobacterial activity.

The natural curcuminoids (I), obtained from the medical plant Curcuma longa L., are structurally modified by alkylation, dealkylation, heterocyclization as well as reduction/oxidation reactions.

Existing macrolides have never shown definitive clinical efficacy in tuberculosis. Recent reports suggest that ribosome methylation is involved in macrolide resistance in Mycobacterium tuberculosis , a mechanism that newer macrolides have been designed to overcome in gram-positive bacteria. Therefore, selected macrolides and ketolides (descladinose) with substitutions at positions 9, 11,12, and 6 were assessed for activity against M. tuberculosis , and those with MICs of ≤4 μM were evaluated for cytotoxicity to Vero cells and J774A.1 macrophages. Several compounds with 9-oxime substitutions or aryl substitutions at position 6 or on 11,12 carbamates or carbazates demonstrated submicromolar MICs. For the three macrolide-ketolide pairs, macrolides demonstrated superior activity. Four compounds with low MICs and low cytotoxicity also effected significant reductions in CFU in infected macrophages. Active compounds were assessed for tolerance and the ability to reduce CFU in the lungs of BALB/c mice in an aerosol infection model. A substituted 11,12 carbazate macrolide demonstrated significant dose-dependent inhibition of M. tuberculosis growth in mice, with a 10- to 20-fold reduction of CFU in lung tissue. Structure-activity relationships, some of which are unique to M. tuberculosis , suggest several synthetic directions for further improvement of antituberculosis activity. This class appears promising for yielding a clinically useful agent for tuberculosis.

The authors describe a rare case of an infection of both the chromomycosis and aspergillosis of the maxillary sinus in an immunocompetent 72-year-old female who presented with progressive visual loss and dull aching pain of the left eye. Sinuscopy of the left maxillary sinus showed swelling of the mucosa with clay-like materials. Biopsy from the left maxillary sinus showed the typically characteristic morphology of chromomycosis and culture from sinus tissue which yielded Aspergillus. The patient responded to a combination therapy of surgical excision and antifungal agent.

Differentiation between Mycobacterium tuberculosis and M. avium is helpful for the treatment of disseminated mycobacterial infection in AIDS patients. This can traditionally be done by time-consuming biochemical tests or with Accuprobe. Previously, PCR restriction enzyme analysis (PCR-REA) of the 16S-23S rRNA gene spacer was shown to be able to identify a limited number of strains of Mycobacterium . In this study the method was improved by using more specific primers and was tested with 50 clinical isolates of M. tuberculosis and 65 clinical isolates of M. avium complex. Probes specific to the spacers of M. tuberculosis and M. avium were also tested. Both M. tuberculosis and M. avium could be reliably identified either by PCR-REA or by PCR-hybridization, with the results completely agreeing with those obtained by biochemical tests and with the Accuprobe, respectively. The method may therefore be useful as an alternative in-house method for identification of the bacteria.