Tuberculosis is still a major health problem worldwide and one of the main causes of death by a single infectious agent. Only few drugs are really effective to treat tuberculosis, hence, the ...emergence of multiple, extensively, and totally drug resistant bacilli compromises the already difficult antituberculosis treatments. Given the persistent global burden of tuberculosis, it is crucial to understand the underlying mechanisms required for the pathogenicity of Mycobacterium tuberculosis (Mtb), the causal agent of tuberculosis, in order to pave the way for developing better drugs and strategies to treat and prevent tuberculosis.
The exclusive mycobacterial cell wall lipids such as trehalose monomycolate and dimycolate (TMM, TDM), phthiocerol dimycocerosate (PDIM), sulpholipid-1 (SL-1), diacyl trehalose (DAT), and pentacyl trehalose (PAT), among others, are known to play an important role in pathogenesis; thus, proteins responsible for their transport are potential virulence factors. MmpL and MmpS proteins mediate transport of important cell wall lipids across the mycobacterial membrane. In Mtb, MmpL3, MmpL7 and MmpL8 transport TMM, PDIM and SL-1 respectively. The translocation of DAT and biosynthesis of PAT is likely due to MmpL10. MmpL and MmpS proteins are involved in other processes such as drug efflux (MmpL5 and MmpL7), siderophore export (MmpL4/MmpS4 and MmpL5/MmpS5), and heme uptake (MmpL3 and MmpL11). Altogether, these proteins can be regarded as new potential targets for antituberculosis drug development. We will review recent advances in developing inhibitors of MmpL proteins, in the challenging context of targeting membrane proteins and the future prospects for potential antituberculosis drug candidates.
Bacterial resistance to antibiotics is widely regarded as a major public health concern with last resort MRSA treatments like vancomycin now encountering resistant strains. TFDs (Transcription Factor ...Decoys) are oligonucleotide copies of the DNA-binding sites for transcription factors. They bind to and sequester the targeted transcription factor, thus inhibiting transcription of many genes. By developing TFDs with sequences aimed at inhibiting transcription factors controlling the expression of highly conserved bacterial cell wall proteins, TFDs present as a potential method for inhibiting microbial growth without encountering typical resistance mechanisms. However, the efficient protection and delivery of the TFDs inside the bacterial cells is a critical step for the success of this technology. Therefore, in our study, specific TFDs against S. aureus were complexed with two different types of nanocarriers: cationic nanostructured lipid carriers (cNLCs) and chitosan-based nanoparticles (CS-NCs). These TFD-carrier nanocomplexes were characterized for size, zeta potential and TFD complexation or loading efficiency in a variety of buffers. In vitro activity of the nanocomplexes was examined alone and in combination with vancomycin, first in methicillin susceptible strains of S. aureus with the lead candidate advancing to tests against MRSA cultures. Results found that both cNLCs and chitosan-based carriers were adept at complexing and protecting TFDs in a range of physiological and microbiological buffers up to 72 hours. From initial testing, chitosan-TFD particles demonstrated no visible improvements in effect when co-administered with vancomycin. However, co-delivery of cNLC-TFD with vancomycin reduced the MIC of vancomycin by over 50% in MSSA and resulted in significant decreases in viability compared with vancomycin alone in MRSA cultures. Furthermore, these TFD-loaded particles demonstrated very low levels of cytotoxicity and haemolysis in vitro. To our knowledge, this is the first attempt at a combined antibiotic/oligonucleotide-TFD approach to combatting MRSA and, as such, highlights a new avenue of MRSA treatment combining traditional small molecules drugs and bacterial gene inhibition.
Antimicrobial resistant (AMR) bacteria constitute a global health concern. Helicobacter pylori is a Gram-negative bacterium that infects about half of the human population and is a major cause of ...peptic ulcer disease and gastric cancer. Increasing resistance to triple and quadruple H. pylori eradication therapies poses great challenges and urges the development of novel, ideally narrow spectrum, antimicrobials targeting H. pylori. Here, we describe the antimicrobial spectrum of a family of nitrobenzoxadiazol-based antimicrobials initially discovered as inhibitors of flavodoxin: an essential H. pylori protein. Two groups of inhibitors are described. One group is formed by narrow-spectrum compounds, highly specific for H. pylori, but ineffective against enterohepatic Helicobacter species and other Gram-negative or Gram-positive bacteria. The second group includes extended-spectrum antimicrobials additionally targeting Gram-positive bacteria, the Gram-negative Campylobacter jejuni, and most Helicobacter species, but not affecting other Gram-negative pathogens. To identify the binding site of the inhibitors in the flavodoxin structure, several H. pylori-flavodoxin variants have been engineered and tested using isothermal titration calorimetry. An initial study of the inhibitors capacity to generate resistances and of their synergism with antimicrobials commonly used in H. pylori eradication therapies is described. The narrow-spectrum inhibitors, which are expected to affect the microbiota less dramatically than current antimicrobial drugs, offer an opportunity to develop new and specific H. pylori eradication combinations to deal with AMR in H. pylori. On the other hand, the extended-spectrum inhibitors constitute a new family of promising antimicrobials, with a potential use against AMR Gram-positive bacterial pathogens.
•Nanoparticles can be used for improving drug efficacy in every field of medicine.•Nanoparticles can have direct antimycobacterial potency or can be carriers of TB drugs.•Each TB drug and drug ...combination requires a dedicated nanoparticle as a carrier.
Therapeutic approaches using nanoparticles are being successfully used in foods and in several fields of medicine, including infectious diseases. Regarding tuberculosis (TB) treatment, nanoparticles can be a useful strategy for two distinct applications: (i) for their intrinsic antimycobacterial activity; (ii) as vehicles for known antitubercular drugs to allow reduction of dose- and drug-associated side-effects and administration via user-friendly administration routes such as pulmonary or oral ones. Promising results were obtained in vitro and in animal Mycobacterium tuberculosis models and need now to be translated into clinical drug candidates. Such a prospect can provide an opportunity regarding the current limited therapeutic options for drug-resistant TB and the scarcity of novel antituberculosis drugs in the drug discovery pipeline.
The intrinsic resistance of mycobacteria to most antimicrobial agents is mainly attributed to the synergy between their relatively impermeable cell wall and efflux systems. The mycobacterial cell ...wall is rich in lipids and polysaccharides making a compact envelope that limits drug uptake. Changes in cell wall composition or structure lead to variations in susceptibility to drugs. Bacterial efflux pumps are membrane proteins that are capable of actively transporting a broad range of substrates, including drugs, from the cytoplasm to the extracellular environment. Increased expression of efflux pump genes confers a low level resistance phenotype, and under these conditions, bacteria may have greater chances of acquiring chromosomal mutation(s) conferring higher levels of drug resistance. In order to develop effective antimycobacterial therapeutic strategies, the contributions to drug resistance made by the limited permeability of the cell wall and the increased expression of efflux pumps must be understood. In this chapter, we describe a method that allows: (1) the quantification of general efflux activity of mycobacterial strains (clinical isolates, mutants impaired in efflux or permeability) by the study of the transport (influx and efflux) of fluorescent compounds, such as ethidium bromide; and (2) the screening of compounds in search of inhibitors of efflux pumps, which could restore the effectiveness of antimicrobials that are subject to efflux.
Abstract
Two mechanisms are thought to be involved in the natural drug resistance of mycobacteria: the mycobacterial cell wall permeability barrier and active multidrug efflux pumps. Genes encoding ...drug efflux transporters have been isolated from several mycobacterial species. These proteins transport tetracycline, fluoroquinolones, aminoglycosides and other compounds. Recent reports have suggested that efflux pumps may also be involved in transporting isoniazid, one of the main drugs used to treat tuberculosis. This review highlights recent advances in our understanding of efflux-mediated drug resistance in mycobacteria, including the distribution of efflux systems in these organisms, their substrate profiles and their contribution to drug resistance. The balance between the drug transport into the cell and drug efflux is not yet clearly understood, and further studies are required in mycobacteria.
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