Infections caused by non-tuberculous mycobacteria (NTM) are increasing globally and are notoriously difficult to treat due to intrinsic resistance of these bacteria to many common antibiotics. NTM ...are diverse and ubiquitous in the environment, with only a few species causing serious and often opportunistic infections in humans, including Mycobacterium abscessus. This rapidly growing mycobacterium is one of the most commonly identified NTM species responsible for severe respiratory, skin and mucosal infections in humans. It is often regarded as one of the most antibiotic-resistant mycobacteria, leaving us with few therapeutic options. In this Review, we cover the proposed infection process of M. abscessus, its virulence factors and host interactions and highlight the commonalities and differences of M. abscessus with other NTM species. Finally, we discuss drug resistance mechanisms and future therapeutic options. Taken together, this knowledge is essential to further our understanding of this overlooked and neglected global threat.
Abstract
Mycobacterium kansasii is a slow-growing nontuberculous mycobacteria responsible for coinfections particularly in patients with human immunodeficiency virus. To date, our knowledge of M. ...kansasii infection has been hampered owing to the lack of an effective animal model to study pathogenesis. In the current study, we showed that the zebrafish embryo is permissive to M. kansasii infection, resulting in chronic infection and formation of granulomas. On macrophage depletion, we identified M. kansasii forms extracellular cords, resulting in acute infection and rapid larval death. These findings highlight the feasibility of zebrafish for studying M. kansasii pathogenesis and for the first time identify extracellular cords in this species.
Summary
Mycobacterial genomes contain large sets of loci encoding membrane proteins that belong to a family of multidrug resistance pumps designated Resistance‐Nodulation‐Cell Division (RND) ...permeases. Mycobacterial membrane protein Large (MmpL) transporters represent a subclass of RND transporters known to participate in the export of lipid components across the cell envelope. These surface‐exposed lipids with unusual structures play key roles in the physiology of mycobacteria and/or can act as virulence factors and immunomodulators. Defining the substrate specificity of MmpLs and their mechanisms of regulation helps understanding how mycobacteria elaborate their complex cell wall. This review describes the diversity of MmpL proteins in mycobacteria, emphasising their high abundance in a few opportunistic rapid‐growing mycobacteria. It reports the conservation of mmpL loci between Mycobacterium tuberculosis and non‐tuberculous mycobacteria, useful in predicting the role of MmpLs with unknown functions. Paradoxically, whereas MmpLs participate in drug resistance mechanisms, they represent also attractive pharmacological targets, opening the way for exciting translational applications. The most recent advances regarding structural/functional information are also provided to explain the molecular basis underlying the proton‐motive force driven lipid transport. Overall, this review emphasises the Janus‐face nature of MmpLs at the crossroads between antibiotic resistance mechanisms and exquisite vulnerability to drugs.
MmpL transporters are membrane proteins, particularly abundant in non‐tuberculous mycobacteria. They are involved in the transport of a diverse family of substrates that include lipid and non‐lipid molecules, required for the cell envelope assembly and/or in growth and pathogenicity. The Janus‐face nature of the MmpL family is supported by their implication in drug resistance mechanisms as well as in the vulnerability of mycobacteria making them attractive drug targets.
Mycobacterium abscessus is a rapidly growing Mycobacterium causing a wide spectrum of clinical syndromes. It now is recognized as a pulmonary pathogen to which cystic fibrosis patients have a ...particular susceptibility. The M. abscessus rough (R) variant, devoid of cell-surface glycopeptidolipids (GPLs), causes more severe clinical disease than the smooth (S) variant, but the underlying mechanisms of R-variant virulence remain obscure. Exploiting the optical transparency of zebrafish embryos, we observed that the increased virulence of the M. abscessus R variant compared with the S variant correlated with the loss of GPL production. The virulence of the R variant involved the massive production of serpentine cords, absent during S-variant infection, and the cords initiated abscess formation leading to rapid larval death. Cording occurred within the vasculature and was highly pronounced in the central nervous system (CNS). It appears that M. abscessus is transported to the CNS within macrophages. The release of M. abscessus from apoptotic macrophages initiated the formation of cords that grew too large to be phagocytized by macrophages or neutrophils. This study is a description of the crucial role of cording in the in vivo physiopathology of M. abscessus infection and emphasizes cording as a mechanism of immune evasion.
Pulmonary infections caused by
are emerging as a global threat, especially in cystic fibrosis patients. Further intensifying the concern of
infection is the recent evidence of human-to-human ...transmission of the infection.
is a naturally multidrug-resistant fast-growing pathogen for which pharmacological options are limited. Repurposing antitubercular drugs represents an attractive option for the development of chemotherapeutic alternatives against
infections. Bedaquiline (BDQ), an ATP synthase inhibitor, has recently been approved for the treatment of multidrug-resistant tuberculosis. Herein, we show that BDQ has a very low MIC against a vast panel of clinical isolates. Despite being bacteriostatic
, BDQ was highly efficacious in a zebrafish model of
infection. Remarkably, a very short period of treatment was sufficient to protect the infected larvae from
-induced killing. This was corroborated with reduced numbers of abscesses and cords, considered to be major pathophysiological signs in infected zebrafish. Mode-of-action studies revealed that BDQ triggered a rapid depletion of ATP in
, consistent with the drug targeting the F
F
ATP synthase. Importantly, despite a failure to select
for spontaneous mutants that are highly resistant to BDQ, the transfer of single nucleotide polymorphisms leading to D29V or A64P substitutions in
conferred high resistance, thus resolving the target of BDQ in
Overall, this study indicates that BDQ is active against
and
and should be considered for clinical use against the difficult-to-manage
pulmonary infections.
Mycobacterium abscessus
is the most common rapidly growing non-tuberculous mycobacteria to cause pulmonary disease in patients with impaired lung function such as cystic fibrosis.
M
.
abscessus
...displays high intrinsic resistance to common antibiotics and inducible resistance to macrolides like clarithromycin. As such,
M
.
abscessus
is clinically resistant to the entire regimen of front-line
M
.
tuberculosis
drugs, and treatment with antibiotics that do inhibit
M
.
abscessus
in the lab results in cure rates of 50% or less. Here, we identified epetraborole (EPT) from the MMV pandemic response box as an inhibitor against the essential protein leucyl-tRNA synthetase (LeuRS) in
M
.
abscessus
. EPT protected zebrafish from lethal
M
.
abscessus
infection and did not induce self-resistance nor against clarithromycin. Contrary to most antimycobacterials, the whole-cell activity of EPT was greater against
M
.
abscessus
than
M
.
tuberculosis
, but crystallographic and equilibrium binding data showed that EPT binds LeuRS
Mabs
and LeuRS
Mtb
with similar residues and dissociation constants. Since EPT-resistant
M
.
abscessus
mutants lost LeuRS editing activity, these mutants became susceptible to misaminoacylation with leucine mimics like the non-proteinogenic amino acid norvaline. Proteomic analysis revealed that when
M
.
abscessus
LeuRS mutants were fed norvaline, leucine residues in proteins were replaced by norvaline, inducing the unfolded protein response with temporal changes in expression of GroEL chaperonins and Clp proteases. This supports our
in vitro
data that supplementation of media with norvaline reduced the emergence of EPT mutants in both
M
.
abscessus
and
M
.
tuberculosis
. Furthermore, the combination of EPT and norvaline had improved
in vivo
efficacy compared to EPT in a murine model of
M
.
abscessus
infection. Our results emphasize the effectiveness of EPT against the clinically relevant cystic fibrosis pathogen
M
.
abscessus
, and these findings also suggest norvaline adjunct therapy with EPT could be beneficial for
M
.
abscessus
and other mycobacterial infections like tuberculosis.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A Cu-mediated azide–alkyne cycloaddition protocol has been employed for the synthesis of 16 different triazoles to probe the antitubercular structure–activity relationships within the ...isatin–ferrocene–triazole conjugate family. The antitubercular evaluation studies revealed a marked improvement in activity with the introduction of ferrocene nucleus among precursors N-alkylazido isatins with a prefernce for halogen (F, Cl) substituent at C-5 position of isatin as well as propyl chain length as a spacer. The induction of a chalcone nucleus resulted in the enhanced antimycobacterial efficacy irrespective of the subtituent and alkyl chain length as evidenced by the isatin–ferrocenylchalcone hybrids. The described protocol is the first successful attempt of the amalgamation of ferrocene–isatin nuclei tethered via a triazole linker.
Mycobacterium abscessus is considered the most common respiratory pathogen among the rapidly growing non-tuberculous mycobacteria. Infections with M. abscessus are increasingly found in patients with ...chronic lung diseases, especially cystic fibrosis, and are often refractory to antibiotic therapy. M. abscessus has two morphotypes with distinct effects on host cells and biological responses. The smooth (S) variant is recognized as the initial airway colonizer while the rough (R) is known to be a potent inflammatory inducer associated with invasive disease, but the underlying immunopathological mechanisms of the infection remain unsolved. We conducted a comparative stepwise dissection of the inflammatory response in S and R pathogenesis by monitoring infected transparent zebrafish embryos. Loss of TNFR1 function resulted in increased mortality with both variants, and was associated with unrestricted intramacrophage bacterial growth and decreased bactericidal activity. The use of transgenic zebrafish lines harboring fluorescent macrophages and neutrophils revealed that neutrophils, like macrophages, interact with M. abscessus at the initial infection sites. Impaired TNF signaling disrupted the IL8-dependent neutrophil mobilization, and the defect in neutrophil trafficking led to the formation of aberrant granulomas, extensive mycobacterial cording, unrestricted bacterial growth and subsequent larval death. Our findings emphasize the central role of neutrophils for the establishment and maintenance of the protective M. abscessus granulomas. These results also suggest that the TNF/IL8 inflammatory axis is necessary for protective immunity against M. abscessus and may be of clinical relevance to explain why immunosuppressive TNF therapy leads to the exacerbation of M. abscessus infections.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Summary
The natural resistance of Mycobacterium abscessus to most commonly available antibiotics seriously limits chemotherapeutic treatment options, which is particularly challenging for cystic ...fibrosis patients infected with this rapid‐growing mycobacterium. New drugs with novel molecular targets are urgently needed against this emerging pathogen. However, the discovery of such new chemotypes has not been appropriately performed. Here, we demonstrate the utility of a phenotypic screen for bactericidal compounds against M. abscessus using a library of compounds previously validated for activity against M. tuberculosis. We identified a new piperidinol‐based molecule, PIPD1, exhibiting potent activity against clinical M. abscessus strains in vitro and in infected macrophages. Treatment of infected zebrafish with PIPD1 correlated with increased embryo survival and decreased bacterial burden. Whole genome analysis of M. abscessus strains resistant to PIPD1 identified several mutations in MAB_4508, encoding a protein homologous to MmpL3. Biochemical analyses demonstrated that while de novo mycolic acid synthesis was unaffected, PIPD1 strongly inhibited the transport of trehalose monomycolate, thereby abrogating mycolylation of arabinogalactan. Mapping the mutations conferring resistance to PIPD1 on a MAB_4508 tridimensional homology model defined a potential PIPD1‐binding pocket. Our data emphasize a yet unexploited chemical structure class against M. abscessus infections with promising translational development possibilities.
The piperidinol‐based lead compound PIPD1 inhibits growth of Mycobacterium abscessus by targeting MAB_4508, an MmpL family member participating in the transport of trehalose monomycolate (TMM), leading to the loss of arabinogalactan mycolylation. Multiple mutations in MAB_4508 conferring high resistance levels to PIPD1 helped to define a potential PIPD1‐binding pocket. Our findings emphasize a yet unexploited chemical structure class against M. abscessus infections with promising translational development possibilities.
is a rapidly-growing species causing a diverse panel of clinical manifestations, ranging from cutaneous infections to severe respiratory disease. Its unique cell wall, contributing largely to drug ...resistance and to pathogenicity, comprises a vast panoply of complex lipids, among which the glycopeptidolipids (GPLs) have been the focus of intense research. These lipids fulfill various important functions, from sliding motility or biofilm formation to interaction with host cells and intramacrophage trafficking. Being highly immunogenic, the induction of a strong humoral response is likely to select for rough low-GPL producers. These, in contrast to the smooth high-GPL producers, display aggregative properties, which strongly impacts upon intracellular survival. A propensity to grow as extracellular cords allows these low-GPL producing bacilli to escape the innate immune defenses. Transitioning from high-GPL to low-GPL producers implicates mutations within genes involved in biosynthesis or transport of GPL. This leads to induction of an intense pro-inflammatory response and robust and lethal infections in animal models, explaining the presence of rough isolates in patients with decreased pulmonary functions. Herein, we will discuss how, thanks to the generation of defined GPL mutants and the development of appropriate cellular and animal models to study pathogenesis, GPL contribute to
biology and physiopathology.
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