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Biofilm growth is thought to be a significant obstacle to the successful treatment of Mycobacterium abscessus infections. A search for agents capable of inhibiting M. abscessus biofilms led to our interest in 2-aminoimidazoles and related scaffolds, which have proven to display antibiofilm properties against a number of Gram-negative and Gram-positive bacteria, including Mycobacterium tuberculosis and Mycobacterium smegmatis. The screening of a library of 30 compounds led to the identification of a compound, AB-2-29, which inhibits the formation of M. abscessus biofilms with an IC50 (the concentration required to inhibit 50% of biofilm formation) in the range of 12.5 to 25 μM. Interestingly, AB-2-29 appears to chelate zinc, and its antibiofilm activity is potentiated by the addition of zinc to the culture medium. Preliminary mechanistic studies indicate that AB-2-29 acts through a distinct mechanism from those reported to date for 2-aminoimidazole compounds. [ABSTRACT FROM AUTHOR]

Abstract Clinical isolates of Mycobacterium tuberculosis and Mycobacterium bovis are differentially susceptible to 2-Thiophen Hydrazide (TCH); however its mechanism of action or the reasons for that difference are unknown. We report herein that under our experimental conditions, TCH inhibits M. tuberculosis in solid but not in liquid medium, and that in spite of resembling Isoniazid and Ethionamide, it does not affect mycolic acid synthesis. To understand the mechanisms of action of TCH we isolated M. tuberculosis TCH resistant mutants which fell into two groups; one resistant to TCH and Isoniazid but not to Ethionamide or Triclosan, and the other resistant only to TCH with no, or marginal, cross resistance to Isoniazid. A S315T katG mutation conferred resistance to TCH while kat G expression from a plasmid reduced M. tuberculosis MIC to this drug, suggesting a possible involvement of KatG in TCH activation. Whole genome sequencing of mutants from this second group revealed a single mutation in the alkylhydroperoxide reductase ahp C promoter locus in half of the mutants, while the remaining contained mutations in dispensable genes. This is the first report of the genetics underlying the action of TCH and of the involvement of ahpC as the sole basis for resistance to an anti-tubercular compound. [ABSTRACT FROM AUTHOR]

It has recently been shown that the anti-mycobacterial pro-drug thiacetazone ( TAC) inhibits the conversion of double bonds of mycolic acid precursors into cyclopropyl rings in Mycobacterium bovis var BCG, M. marimum and M. chelonae by affecting the cyclopropyl mycolic acid synthases ( CMASs) as judged by the build-up of unsaturated mycolate precursors. In our hands, TAC inhibits mycolic acid biosynthesis in Mycobacterium tuberculosis and M. kansasii with almost negligible accumulation of those precursors. Our observations that ' de novo' biosynthesis of all the mycolic acid families decreased upon TAC treatment prompted us to analyse the role of each one of the Type II Fatty Acid Synthase ( FASII) enzymes. Overexpression of the hadABC operon, encoding the essential FASII dehydratase complex, but not of any of the remaining FASII genes acting on the elongation of fatty acyl chains leading to the synthesis of meromycolic acids, resulted in high level of resistance to TAC in M. tuberculosis. Spontaneous M. tuberculosis and M. kansasii TAC-resistant mutants isolated during this work revealed mutations in the hadABC genes strongly supporting our proposal that these enzymes are new players in the resistance to this anti-mycobacterial compound. [ABSTRACT FROM AUTHOR]

There is an urgent need to develop new drug treatment strategies to control the global spread of drug-sensitive and multidrug-resistant Mycobacterium tuberculosis (M. tuberculosis). The ß-lactam class of antibiotics is among the safest and most widely prescribed antibiotics, but they are not effective against M. tuberculosis due to intrinsic resistance. This study shows that 2-aminoimidazole (2-AI)-based small molecules potentiate ß-lactam antibiotics against M. tuberculosis. Active 2-AI compounds significantly reduced the minimal inhibitory and bactericidal concentrations of ß-lactams by increasing M. tuberculosis cell envelope permeability and decreasing protein secretion including ß-lactamase. Metabolic labeling and transcriptional profiling experiments revealed that 2-AI compounds impair mycolic acid biosynthesis, export and linkage to the mycobacterial envelope, counteracting an important defense mechanism reducing permeability to external agents. Additionally, other important constituents of the M. tuberculosis outer membrane including sulfolipid-1 and polyacyltrehalose were also less abundant in 2-AI treated bacilli. As a consequence of 2-AI treatment, M. tuberculosis displayed increased sensitivity to SDS, increased permeability to nucleic acid staining dyes, and rapid binding of cell wall targeting antibiotics. Transcriptional profiling analysis further confirmed that 2-AI induces transcriptional regulators associated with cell envelope stress. 2-AI based small molecules potentiate the antimicrobial activity of ß-lactams by a mechanism that is distinct from specific inhibitors of ß-lactamase activity and therefore may have value as an adjunctive anti-TB treatment. [ABSTRACT FROM AUTHOR]

Abstract: In this work, the antitubercular activity of a pentacyano(isoniazid)ferrate(II) compound (IQG-607) was investigated using a macrophage model of Mycobacterium tuberculosis infection. Importantly, treatment of M.-tuberculosis-infected macrophages with IQG-607 significantly diminished the number of CFU compared with the untreated control group. The antitubercular activity of IQG-607 was similar to that observed for the positive control drugs isoniazid and rifampicin. Nevertheless, higher concentrations of IQG-607 produced a significantly greater reduction in bacterial load compared with the same concentrations of isoniazid. Analysis of the mechanism of action of IQG-607 revealed that the biosynthesis of mycolic acids was blocked. The promising activity of IQG-607 in infected macrophages and the experimental determination of its mechanism of action may help in further studies aimed at the development of a new antimycobacterial agent. [Copyright &y& Elsevier]

Isoxyl (ISO) and thiacetazone (TAC), two prodrugs once used in the clinical treatment of tuberculosis, have long been thought to abolish Mycobacterium tuberculosis (M. tuberculosis) growth through the inhibition of mycolic acid biosynthesis, but their respective targets in this pathway have remained elusive. Here we show that treating M. tuberculosis with ISO orTACresults in both cases in the accumulation of 3-hydroxy C18, C20, and C22 fatty acids, suggestive of an inhibition of the dehydratase step of the fatty-acid synthase type II elongation cycle. Consistently, overexpression of the essential hadABC genes encoding the (3R)-hydroxyacyl-acyl carrier protein dehydratases resulted in more than a 16- and 80-fold increase in the resistance of M. tuberculosis to ISO and TAC, respectively. Amissense mutation in the had A gene of spontaneous ISO- and TAC-resistant mutants was sufficient to confer upon M. tuberculosis high level resistance to both drugs. Other mutations found in hypersusceptible or resistant M. tuberculosis and Mycobacterium kansasii isolates mapped to hadC. Mutations affecting the non-essential mycolic acid methyltransferases MmaA4 and MmaA2 were also found in M. tuberculosis spontaneous ISO- and TAC-resistant mutants. That MmaA4, at least, participates in the activation of the two prodrugs as proposed earlier is not supported by our biochemical evidence. Instead and in light of the known interactions of both MmaA4 and MmaA2 with HadAB and HadBC, we propose that mutations affecting these enzymes may impact the binding of ISO and TAC to the dehydratases. [ABSTRACT FROM AUTHOR]