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.
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.
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.
Free-living amoebae are thought to represent an environmental niche in which amoeba-resistant bacteria may evolve towards pathogenicity. To get more insights into factors playing a role for ...adaptation to intracellular life, we characterized the transcriptomic activities of the emerging pathogen Mycobacterium abscessus in amoeba and murine macrophages (Mϕ) and compared them with the intra-amoebal transcriptome of the closely related, but less pathogenic Mycobacterium chelonae. Data on up-regulated genes in amoeba point to proteins that allow M. abscessus to resist environmental stress and induce defense mechanisms, as well as showing a switch from carbohydrate carbon sources to fatty acid metabolism. For eleven of the most upregulated genes in amoeba and/or Mϕ, we generated individual gene knock-out M. abscessus mutant strains, from which ten were found to be attenuated in amoeba and/or Mϕ in subsequence virulence analyses. Moreover, transfer of two of these genes into the genome of M. chelonae increased the intra-Mϕ survival of the recombinant strain. One knock-out mutant that had the gene encoding Eis N-acetyl transferase protein (MAB_4532c) deleted, was particularly strongly attenuated in Mϕ. Taken together, M. abscessus intra-amoeba and intra-Mϕ transcriptomes revealed the capacity of M. abscessus to adapt to an intracellular lifestyle, with amoeba largely contributing to the enhancement of M. abscessus intra-Mϕ survival.
Mycobacterium abscessus is an emerging rapidly growing mycobacterium (RGM) causing a pseudotuberculous lung disease to which patients with cystic fibrosis (CF) are particularly susceptible. We report ...here its complete genome sequence. The genome of M. abscessus (CIP 104536T) consists of a 5,067,172-bp circular chromosome including 4920 predicted coding sequences (CDS), an 81-kb full-length prophage and 5 IS elements, and a 23-kb mercury resistance plasmid almost identical to pMM23 from Mycobacterium marinum. The chromosome encodes many virulence proteins and virulence protein families absent or present in only small numbers in the model RGM species Mycobacterium smegmatis. Many of these proteins are encoded by genes belonging to a "mycobacterial" gene pool (e.g. PE and PPE proteins, MCE and YrbE proteins, lipoprotein LpqH precursors). However, many others (e.g. phospholipase C, MgtC, MsrA, ABC Fe(3+) transporter) appear to have been horizontally acquired from distantly related environmental bacteria with a high G+C content, mostly actinobacteria (e.g. Rhodococcus sp., Streptomyces sp.) and pseudomonads. We also identified several metabolic regions acquired from actinobacteria and pseudomonads (relating to phenazine biosynthesis, homogentisate catabolism, phenylacetic acid degradation, DNA degradation) not present in the M. smegmatis genome. Many of the "non mycobacterial" factors detected in M. abscessus are also present in two of the pathogens most frequently isolated from CF patients, Pseudomonas aeruginosa and Burkholderia cepacia. This study elucidates the genetic basis of the unique pathogenicity of M. abscessus among RGM, and raises the question of similar mechanisms of pathogenicity shared by unrelated organisms in CF patients.
Mycobacterium abscessus belongs to the largest group of mycobacteria, the rapid-growing saprophytic mycobacteria, and is one of the most difficult-to-treat opportunistic pathogen. Several features ...pertain to the high adaptability of M. abscessus to the host. These include the capacity to survive and persist within amoebae, to transition from a smooth to a rough morphotype that occurs during the course of the disease and to express of a wide array of virulence factors.
The main objective of this narrative review consists to report major assets of M. abscessus that contribute to the virulence of these rapid-growing saprophytic mycobacteria. Strikingly, many of these determinants, whether they are from a mycobacterial origin or acquired by horizontal gene transfer, are known virulence factors found in slow-growing and strict pathogens for humans and animals.
In the light of recent published work in the field we attempted to highlight major features characterizing M. abscessus pathogenicity and to explain why this led to the emergence of this mycobacterial species in patients with cystic fibrosis.
M. abscessus genome plasticity, the smooth-to-rough transition, and the expression of a panel of enzymes associated with virulence in other bacteria are key players in M. abscessus virulence. In addition, the very large repertoire of lipid transporters, known as mycobacterial membrane protein large and small (MmpL and MmpS respectively), deeply influences the pathogenicity of M. abscessus, as exemplified here for some of them.
All these traits largely contribute to make M. abscessus a unique mycobacterium regarding to its pathophysiological processes, ranging from the early colonization steps to the establishment of severe and chronic pulmonary diseases.
A general method is proposed to produce oriented and highly crystalline conducting polymer layers. It combines the controlled orientation/crystallization of polymer films by high‐temperature rubbing ...with a soft‐doping method based on spin‐coating a solution of dopants in an orthogonal solvent. Doping rubbed films of regioregular poly(3‐alkylthiophene)s and poly(2,5‐bis(3‐dodecylthiophen‐2‐yl)thieno3,2‐bthiophene) with 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F4TCNQ) yields highly oriented conducting polymer films that display polarized UV–visible–near‐infrared (NIR) absorption, anisotropy in charge transport, and thermoelectric properties. Transmission electron microscopy and polarized UV–vis–NIR spectroscopy help understand and clarify the structure of the films and the doping mechanism. F4TCNQ− anions are incorporated into the layers of side chains and orient with their long molecular axis perpendicular to the polymer chains. The ordering of dopant molecules depends closely on the length and packing of the alkyl side chains. Increasing the dopant concentration results in a continuous variation of unit cell parameters of the doped phase. The high orientation results in anisotropic charge conductivity (σ) and thermoelectric properties that are both enhanced in the direction of the polymer chains (σ = 22 ± 5 S cm−1 and S = 60 ± 2 µV K−1). The method of fabrication of such highly oriented conducting polymer films is versatile and is applicable to a large palette of semiconducting polymers.
A versatile method is proposed to produce oriented and crystalline conducting polymer films. It combines alignment of semiconducting polymers by high‐temperature rubbing with a soft‐doping method. The oriented films show important anisotropy of UV–vis–near‐infrared absorption, charge conductivity, and thermoelectric properties. The polymer side chain packing plays a key role on the intercalation of dopant molecules in the host polymer.
We performed a multicenter prevalence study of nontuberculous mycobacteria (NTM) involving 1,582 patients (mean age, 18.9 years; male/female ratio, 1.06) with cystic fibrosis in France. The overall ...NTM prevalence (percentage of patients with at least one positive culture) was 6.6% (104/1,582 patients), with prevalences ranging from 3.7% (in the east of France) to 9.6% (in the greater Paris area). Mycobacterium abscessus complex (MABSC; 50 patients) and Mycobacterium avium complex (MAC; 23 patients) species were the most common NTM, and the only ones associated with fulfillment of the American Thoracic Society bacteriological criteria for NTM lung disease. The "new" species, Mycobacterium bolletii and Mycobacterium massiliense, accounted for 40% of MABSC isolates. MABSC species were isolated at all ages, with a prevalence peak between 11 and 15 years of age (5.8%), while MAC species reached their highest prevalence value among patients over 25 years of age (2.2%).
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.
Summary
Mycobacterium abscessus is an emerging pathogen that is increasingly recognized as a relevant cause of human lung infection in cystic fibrosis patients. This highly antibiotic‐resistant ...mycobacterium is an exception within the rapidly growing mycobacteria, which are mainly saprophytic and non‐pathogenic organisms. M. abscessus manifests as either a smooth (S) or a rough (R) colony morphotype, which is of clinical importance as R morphotypes are associated with more severe and persistent infections. To better understand the molecular mechanisms behind the S/R alterations, we analysed S and R variants of three isogenic M. abscessus S/R pairs using an unbiased approach involving genome and transcriptome analyses, transcriptional fusions and integrating constructs. This revealed different small insertions, deletions (indels) or single nucleotide polymorphisms within the non‐ribosomal peptide synthase gene cluster mps1‐mps2‐gap or mmpl4b in the three R variants, consistent with the transcriptional differences identified within this genomic locus that is implicated in the synthesis and transport of Glyco‐Peptido‐Lipids (GPL). In contrast to previous reports, the identification of clearly defined genetic lesions responsible for the loss of GPL‐production or transport makes a frequent switching back‐and‐forth between smooth and rough morphologies in M. abscessus highly unlikely, which is important for our understanding of persistent M. abscessus infections.
PDF
