Non mycobacterial virulence genes in the genome of the emerging pathogen Mycobacterium abscessus

Transcription and translation of the rpsJ, rplN and rRNA operons of the tubercle bacillus

Several species of the genus Mycobacterium are human pathogens, notably the tubercle bacillus (Mycobacterium tuberculosis). The rate of proliferation of a bacterium is reflected in the rate of ribosome synthesis. This report describes a quantitative analysis of the early stages of the synthesis of ribosomes of M. tuberculosis. Specifically, the roles of three large operons, namely: the rrn operon (1.7 microns) encoding rrs (16S rRNA), rrl (23S rRNA) and rrf (5S rRNA); the rpsJ operon (1.93 microns), which encodes 11 ribosomal proteins; and the rplN operon (1.45 microns), which encodes 10 ribosomal proteins. A mathematical framework based on properties of population-average cells was developed to identify the number of transcripts of the rpsJ and rplN operons needed to maintain exponential growth. The values obtained were supported by RNaseq data. The motif 5'-gcagac-3' was found close to 5' end of transcripts of mycobacterial rplN operons, suggesting it may form part of the RpsH feedback binding site because the same motif is present in the ribosome within the region of rrs that forms the binding site for RpsH.

Structure of mycobacterial maltokinase, the missing link in the essential GlgE-pathway

A novel four-step pathway identified recently in mycobacteria channels trehalose to glycogen synthesis and is also likely involved in the biosynthesis of two other crucial polymers: intracellular methylglucose lipopolysaccharides and exposed capsular glucan. The structures of three of the intervening enzymes - GlgB, GlgE, and TreS - were recently reported, providing the first templates for rational drug design. Here we describe the structural characterization of the fourth enzyme of the pathway, mycobacterial maltokinase (Mak), uncovering a eukaryotic-like kinase (ELK) fold, similar to methylthioribose kinases and aminoglycoside phosphotransferases. The 1.15 Å structure of Mak in complex with a non-hydrolysable ATP analog reveals subtle structural rearrangements upon nucleotide binding in the cleft between the N- and the C-terminal lobes. Remarkably, this new family of ELKs has a novel N-terminal domain topologically resembling the cystatin family of protease inhibitors. By interfacing with and restraining the mobility of the phosphate-binding region of the N-terminal lobe, Mak's unusual N-terminal domain might regulate its phosphotransfer activity and represents the most likely anchoring point for TreS, the upstream enzyme in the pathway. By completing the gallery of atomic-detail models of an essential pathway, this structure opens new avenues for the rational design of alternative anti-tubercular compounds.

High-level relatedness among Mycobacterium abscessus subsp. massiliense strains from widely separated outbreaks

Three recently sequenced strains isolated from patients during an outbreak of Mycobacterium abscessus subsp. massiliense infections at a cystic fibrosis center in the United States were compared with 6 strains from an outbreak at a cystic fibrosis center in the United Kingdom and worldwide strains. Strains from the 2 cystic fibrosis outbreaks showed high-level relatedness with each other and major-level relatedness with strains that caused soft tissue infections during an epidemic in Brazil. We identified unique single-nucleotide polymorphisms in cystic fibrosis and soft tissue outbreak strains, separate single-nucleotide polymorphisms only in cystic fibrosis outbreak strains, and unique genomic traits for each subset of isolates. Our findings highlight the necessity of identifying M. abscessus to the subspecies level and screening all cystic fibrosis isolates for relatedness to these outbreak strains. We propose 2 diagnostic strategies that use partial sequencing of rpoB and secA1 genes and a multilocus sequence typing protocol.

Aminoglycoside-modifying enzymes determine the innate susceptibility to aminoglycoside antibiotics in rapidly growing mycobacteria

OBJECTIVES

Infections caused by the rapidly growing mycobacterium (RGM) Mycobacterium abscessus are notoriously difficult to treat due to the innate resistance of M. abscessus to most clinically available antimicrobials. Aminoglycoside antibiotics (AGA) are a cornerstone of antimicrobial chemotherapy against M. abscessus infections, although little is known about intrinsic drug resistance mechanisms. We investigated the role of chromosomally encoded putative aminoglycoside-modifying enzymes (AME) in AGA susceptibility in M. abscessus.

METHODS

Clinical isolates of M. abscessus were tested for susceptibility to a series of AGA with different substituents at positions 2', 3' and 4' of ring 1 in MIC assays. Cell-free extracts of M. abscessus type strain ATCC 19977 and Mycobacterium smegmatis strains SZ380 [aac(2')-Id(+)], EP10 [aac(2')-Id(-)] and SZ461 [aac(2')-Id(+), rrs A1408G] were investigated for AGA acetylation activity using thin-layer chromatography (TLC). Cell-free ribosome translation assays were performed to directly study drug-target interaction.

RESULTS

Cell-free translation assays demonstrated that ribosomes of M. abscessus and M. smegmatis show comparable susceptibility to all tested AGA. MIC assays for M. abscessus and M. smegmatis, however, consistently showed the lowest MIC values for 2'-hydroxy-AGA as compared with 2'-amino-AGA, indicating that an aminoglycoside-2'-acetyltransferase, Aac(2'), contributes to innate AGA susceptibility. TLC experiments confirmed enzymatic activity consistent with Aac(2'). Using M. smegmatis as a model for RGM, acetyltransferase activity was shown to be up-regulated in response to AGA-induced inhibition of protein synthesis.

CONCLUSIONS

Our findings point to AME as important determinants of AGA susceptibility in M. abscessus.

Microbial Proteome Profiling and Systems Biology: Applications to Mycobacterium tuberculosis

Each year, 1.3 million people die from tuberculosis, an infectious disease caused by Mycobacterium tuberculosis. Systems biology-based strategies might significantly contribute to the knowledge-guided development of more effective vaccines and drugs to prevent and cure infectious diseases. To build models simulating the behaviour of a system in response to internal or external stimuli and to identify potential targets for therapeutic intervention, systems biology approaches require the acquisition of quantitative molecular profiles on many perturbed states. Here we review the current state of proteomic analyses in Mycobacterium tuberculosis and discuss the potential of recently emerging targeting mass spectrometry-based techniques which enable fast, sensitive and accurate protein measurements.

β-Lactamase inhibition by avibactam in Mycobacterium abscessus

OBJECTIVES

Two β-lactams, cefoxitin and imipenem, are part of the reference treatment for pulmonary infections with Mycobacterium abscessus. M. abscessus has recently been shown to produce a broad-spectrum β-lactamase, BlaMab, indicating that the combination of β-lactams with a BlaMab inhibitor may improve treatment efficacy. The objectives of this study were to evaluate the impact of BlaMab production on the efficacy of β-lactams in vitro and to assess the benefit of BlaMab inhibition on the activity of β-lactams intracellularly and in an animal model.

METHODS

We analysed the mechanism and kinetics of BlaMab inactivation by avibactam, a non-β-lactam β-lactamase inhibitor currently in Phase III of development, in combination with ceftazidime for the treatment of serious infections due to Gram-negative bacteria. We then deleted the gene encoding BlaMab to assess the extent of BlaMab inhibition by avibactam based on a comparison of the impact of chemical and genetic inactivation. Finally, the efficacy of amoxicillin in combination with avibactam was evaluated in cultured human macrophages and in a zebrafish model of M. abscessus infection.

RESULTS

We showed that avibactam efficiently inactivated BlaMab via the reversible formation of a covalent adduct. An inhibition of BlaMab by avibactam was observed in both infected macrophages and zebrafish.

CONCLUSIONS

Our data identify avibactam as the first efficient inhibitor of BlaMab and strongly suggest that β-lactamase inhibition should be evaluated to provide improved therapeutic options for M. abscessus infections.

Complete genome sequence and comparative genomic analysis of Mycobacterium massiliense JCM 15300 in the Mycobacterium abscessus group reveal a conserved genomic island MmGI-1 related to putative lipid metabolism

Mycobacterium abscessus group subsp., such as M. massiliense, M. abscessus sensu stricto and M. bolletii, are an environmental organism found in soil, water and other ecological niches, and have been isolated from respiratory tract infection, skin and soft tissue infection, postoperative infection of cosmetic surgery. To determine the unique genetic feature of M. massiliense, we sequenced the complete genome of M. massiliense type strain JCM 15300 (corresponding to CCUG 48898). Comparative genomic analysis was performed among Mycobacterium spp. and among M. abscessus group subspp., showing that additional ß-oxidation-related genes and, notably, the mammalian cell entry (mce) operon were located on a genomic island, M. massiliense Genomic Island 1 (MmGI-1), in M. massiliense. In addition, putative anaerobic respiration system-related genes and additional mycolic acid cyclopropane synthetase-related genes were found uniquely in M. massiliense. Japanese isolates of M. massiliense also frequently possess the MmGI-1 (14/44, approximately 32%) and three unique conserved regions (26/44; approximately 60%, 34/44; approximately 77% and 40/44; approximately 91%), as well as isolates of other countries (Malaysia, France, United Kingdom and United States). The well-conserved genomic island MmGI-1 may play an important role in high growth potential with additional lipid metabolism, extra factors for survival in the environment or synthesis of complex membrane-associated lipids. ORFs on MmGI-1 showed similarities to ORFs of phylogenetically distant M. avium complex (MAC), suggesting that horizontal gene transfer or genetic recombination events might have occurred within MmGI-1 among M. massiliense and MAC.

Mycobacterium abscessus phospholipase C expression is induced during coculture within amoebae and enhances M. abscessus virulence in mice

Mycobacterium abscessus is a pathogenic, rapidly growing mycobacterium involved in pulmonary and cutaneo-mucous infections worldwide, to which cystic fibrosis patients are exquisitely susceptible. The analysis of the genome sequence of M. abscessus showed that this bacterium is endowed with the metabolic pathways typically found in environmental microorganisms that come into contact with soil, plants, and aquatic environments, where free-living amoebae are frequently present. M. abscessus also contains several genes that are characteristically found only in pathogenic bacteria. One of them is MAB_0555, encoding a putative phospholipase C (PLC) that is absent from most other rapidly growing mycobacteria, including Mycobacterium chelonae and Mycobacterium smegmatis. Here, we report that purified recombinant M. abscessus PLC is highly cytotoxic to mouse macrophages, presumably due to hydrolysis of membrane phospholipids. We further showed by constructing and using an M. abscessus PLC knockout mutant that loss of PLC activity is deleterious to M. abscessus intracellular survival in amoebae. The importance of PLC is further supported by the fact that M. abscessus PLC was found to be expressed only in amoebae. Aerosol challenge of mice with M. abscessus strains that were precultured in amoebae enhanced M. abscessus lung infectivity relative to M. abscessus grown in broth culture. Our study underlines the importance of PLC for the virulence of M. abscessus. Despite the difficulties of isolating M. abscessus from environmental sources, our findings suggest that M. abscessus has evolved in close contact with environmental protozoa, which supports the argument that amoebae may contribute to the virulence of opportunistic mycobacteria.

Whole-genome sequencing and epidemiological analysis do not provide evidence for cross-transmission of mycobacterium abscessus in a cohort of pediatric cystic fibrosis patients

We have not been able to demonstrate cross-transmission of Mycobacterium abscessus within our hospital, except between siblings who had intense contact in the home environment. The role of the environment in the acquisition of M. abscessus infection requires further investigation.

Background. Mycobacterium abscessus has emerged as a major pathogen in cystic fibrosis (CF) patients and has been associated with poor clinical outcomes, particularly following lung transplant. We investigated the acquisition of this bacterium in a cohort of pediatric CF patients.

Methods. Demographic and patient location data were used to uncover epidemiological links between patients with genetically related strains of M. abscessus that had been previously typed by variable-number tandem repeat profiling. Whole-genome sequencing was applied to 27 M. abscessus isolates from the 20 patients in this cohort to provide definitive data on the genetic relatedness of strains.

Results. Whole-genome sequencing data demonstrated that M. abscessus isolates from 16 patients were unrelated, differing by at least 34 single-nucleotide polymorphisms (SNPs) from any other isolate, suggesting that independent acquisition events have occurred. Only 2 clusters of very closely related (<25 SNPs) isolates from different patients were seen. The first cluster contained 8 isolates, differing by a maximum of 17 SNPs, from a sibling pair who had intense exposure to each other both inside and outside the hospital. The second cluster contained 3 isolates, differing by a maximum of 24 SNPs, from 2 individuals with no apparent epidemiological links.

Conclusions. We have not demonstrated cross-transmission of M. abscessus within our hospital, except between 1 sibling pair. Alternative routes of acquisition of M. abscessus infection, in particular the environment, require further investigation.

Bacterial antimicrobial metal ion resistance

Metals such as mercury, arsenic, copper and silver have been used in various forms as antimicrobials for thousands of years with until recently, little understanding of their mode of action. The discovery of antibiotics and new organic antimicrobial compounds during the twentieth century saw a general decline in the clinical use of antimicrobial metal compounds, with the exception of the rediscovery of the use of silver for burns treatments and niche uses for other metal compounds. Antibiotics and new antimicrobials were regarded as being safer for the patient and more effective than the metal-based compounds they supplanted. Bacterial metal ion resistances were first discovered in the second half of the twentieth century. The detailed mechanisms of resistance have now been characterized in a wide range of bacteria. As the use of antimicrobial metals is limited, it is legitimate to ask: are antimicrobial metal resistances in pathogenic and commensal bacteria important now? This review details the new, rediscovered and 'never went away' uses of antimicrobial metals; examines the prevalence and linkage of antimicrobial metal resistance genes to other antimicrobial resistance genes; and examines the evidence for horizontal transfer of these genes between bacteria. Finally, we discuss the possible implications of the widespread dissemination of these resistances on re-emergent uses of antimicrobial metals and how this could impact upon the antibiotic resistance problem.

Recent progress towards understanding genetic variation in the Mycobacterium abscessus complex

Mycobacterium abscessus is an emerging cause of respiratory disease and soft tissue infections. Whole genome sequencing and other molecular approaches are enhancing our understanding of outbreaks, antibiotic resistance mechanisms, and virulence properties, and of the phylogeny of the M. abscessus complex. Infection models are providing further insights into factors such as colony phenotype that impact host-pathogen interactions. This paper reviews recent developments in our understanding of genetic variation in M. abscessus and the potential relevance for disease and treatment.

Distribution of horizontally transferred heavy metal resistance operons in recent outbreak bacteria

Mankind is confronted by the outbreaks of highly virulent and multi-drug resistant pathogens. The outbreak strains often belong to well-known diseases associated species such as Salmonella, Klebsiella and Mycobacterium, but even normally commensal and environmental microorganisms may suddenly acquire properties of virulent bacteria and cause nosocomial infections. The acquired virulence is often associated with lateral exchange of pathogenicity genomic islands containing drug and heavy metal resistance determinants. Metal ions are used by the immune system of macro-organisms against bactericidal agents. The ability to control heavy metal homeostasis is a factor that allows the survival of pathogenic microorganisms in macrophages. In this paper, we investigate the origin of heavy metal resistance operons in the recent outbreak strains and the possible routes which may lead to acquisitions of these genes by potentially new pathogens. We hypothesize that new outbreak microorganisms appear intermittently on an intersection of the non-specialized, genetically naïve strains of potential pathogens and virulence factor comprising vectors (plasmid and/or phages) newly generated in the environmental microflora. Global contamination of the environment and climate change may also have an effect toward the acceleration and appearance of new pathogens.

Structural and functional characterization of an arylamineN-acetyltransferase from the pathogenMycobacterium abscessus: differences from other mycobacterial isoforms and implications for selective inhibition

Mycobacterium abscessusis the most pathogenic rapid-growing mycobacterium and is one of the most resistant organisms to chemotherapeutic agents. However, structural and functional studies ofM. abscessusproteins that could modify/inactivate antibiotics remain nonexistent. Here, the structural and functional characterization of an arylamineN-acetyltransferase (NAT) fromM. abscessus[(MYCAB)NAT1] are reported. This novel prokaryotic NAT displays significantN-acetyltransferase activity towards aromatic substrates, including antibiotics such as isoniazid andp-aminosalicylate. The enzyme is endogenously expressed and functional in both the rough and smoothM. abscessusmorphotypes. The crystal structure of (MYCAB)NAT1 at 1.8 Å resolution reveals that it is more closely related toNocardia farcinicaNAT than to mycobacterial isoforms. In particular, structural and physicochemical differences from other mycobacterial NATs were found in the active site. Peculiarities of (MYCAB)NAT1 were further supported by kinetic and docking studies showing that the enzyme was poorly inhibited by the piperidinol inhibitor of mycobacterial NATs. This study describes the first structure of an antibiotic-modifying enzyme fromM. abscessusand provides bases to better understand the substrate/inhibitor-binding specificities among mycobacterial NATs and to identify/optimize specific inhibitors. These data should also contribute to the understanding of the mechanisms that are responsible for the pathogenicity and extensive chemotherapeutic resistance ofM. abscessus.

Mycobacteriophage-drived diversification of Mycobacterium abscessus

Background

Mycobacterium abscessus is an emerging opportunistic pathogen which diversity was acknowledged by the recent description of two subspecies accommodating M. abscessus, Mycobacterium bolletii and Mycobacterium massiliense isolates.

Results

Here, genome analysis found 1–8 prophage regions in 47/48 M. abscessus genomes ranging from small prophage-like elements to complete prophages. A total of 20,304 viral and phage proteins clustered into 853 orthologous groups. Phylogenomic and phylogenetic analyses based on prophage region homology found three main clusters corresponding to M. abscessus, M. bolletii and M. massiliense. Analysing 135 annotated Tape Measure Proteins found thirteen clusters and four singletons, suggesting that at least 17 mycobacteriophages had infected M. abscessus during its evolution. The evolutionary history of phages differed from that of their mycobacterial hosts. In particular, 33 phage-related proteins have been horizontally transferred within M. abscessus genomes. They comprise of an integrase, specific mycobacteriophage proteins, hypothetical proteins and DNA replication and metabolism proteins. Gene exchanges, loss and gains which occurred in M. abscessus genomes have been driven by several mycobacteriophages.

Conclusions

This analysis of phage-mycobacterium co-evolution suggests that mycobacteriophages are playing a key-role in the on-going diversification of M. abscessus.

Reviewers

This article was reviewed by Eric Bapteste, Patrick Forterre and Eugene Koonin.

Genomic signatures of distributive conjugal transfer among mycobacteria

Distributive conjugal transfer (DCT) is a newly described mechanism of lateral gene transfer (LGT) that results in a mosaic transconjugant structure, similar to the products of meiosis. We have tested popular LGT detection methods on whole-genome sequence data from experimental DCT transconjugants and used the best performing methods to compare genomic signatures of DCT with those of LGT through natural transformation, conjugative plasmids, and mobile genetic elements (MGE). We found that DCT results in transfer of larger chromosomal segments, that these segments are distributed more broadly around the chromosome, and that a greater proportion of the chromosome is affected by DCT than by other mechanisms of LGT. We used the best performing methods to characterize LGT in Mycobacterium canettii, the mycobacterial species most closely related to Mycobacterium tuberculosis. Patterns of LGT among M. canettii were highly distinctive. Gene flow appeared unidirectional, from lineages with minimal evidence of LGT to isolates with a substantial proportion (6–13%) of sites identified as recombinant. Among M. canettii isolates with evidence of LGT, recombinant fragments were larger and more evenly distributed relative to bacteria that undergo LGT through natural transformation, conjugative plasmids, and MGE. Spatial bias in M. canettii was also unusual in that patterns of recombinant fragment sharing mirrored overall phylogenetic structure. Based on the proportion of recombinant sites, the size of recombinant fragments, their spatial distribution and lack of association with MGE, as well as unidirectionality of DNA transfer, we conclude that DCT is the predominant mechanism of LGT among M. canettii.

Antimicrobial resistance in the respiratory microbiota of people with cystic fibrosis

Cystic fibrosis is characterised by chronic polymicrobial infection and inflammation in the airways of patients. Antibiotic treatment regimens, targeting recognised pathogens, have substantially contributed to increased life expectancy of patients with this disease. Although the emergence of antimicrobial resistance and selection of highly antibiotic-resistant bacterial strains is of major concern, the clinical relevance in cystic fibrosis is yet to be defined. Resistance has been identified in recognised cystic fibrosis pathogens and in other bacteria (eg, Prevotella and Streptococcus spp) detected in the airway microbiota, but their role in the pathophysiology of infection and inflammation in chronic lung disease is unclear. Increased antibiotic resistance in cystic fibrosis might be attributed to a range of complex factors including horizontal gene transfer, hypoxia, and biofilm formation. Strategies to manage antimicrobial resistance consist of new antibiotics or localised delivery of antimicrobial agents, iron sequestration, inhibition of quorum-sensing, and resistome analysis. Determination of the contributions of every bacterial species to lung health or disease in cystic fibrosis might also have an important role in the management of antibiotic resistance.

Genome sequencing of Mycobacterium abscessus isolates from patients in the united states and comparisons to globally diverse clinical strains

Nontuberculous mycobacterial infections caused by Mycobacterium abscessus are responsible for a range of disease manifestations from pulmonary to skin infections and are notoriously difficult to treat, due to innate resistance to many antibiotics. Previous population studies of clinical M. abscessus isolates utilized multilocus sequence typing or pulsed-field gel electrophoresis, but high-resolution examinations of genetic diversity at the whole-genome level have not been well characterized, particularly among clinical isolates derived in the United States. We performed whole-genome sequencing of 11 clinical M. abscessus isolates derived from eight U.S. patients with pulmonary nontuberculous mycobacterial infections, compared them to 30 globally diverse clinical isolates, and investigated intrapatient genomic diversity and evolution. Phylogenomic analyses revealed a cluster of closely related U.S. and Western European M. abscessus subsp. abscessus isolates that are genetically distinct from other European isolates and all Asian isolates. Large-scale variation analyses suggested genome content differences of 0.3 to 8.3%, relative to the reference strain ATCC 19977(T). Longitudinally sampled isolates showed very few single-nucleotide polymorphisms and correlated genomic deletion patterns, suggesting homogeneous infection populations. Our study explores the genomic diversity of clinical M. abscessus strains from multiple continents and provides insight into the genome plasticity of an opportunistic pathogen.

Analysis of species and intra-species associations between the Mycobacterium abscessus complex strains using pulsed-field gel electrophoresis (PFGE) and multi-locus sequence typing (MLST)

PFGE and MLST showed that the strains of M. massiliense hsp65 II-1 were clearly separated from the strains of M. massiliense hsp65 I or II-2 as well as the strains of M. abscessus or M. bolletii; thus, M. massiliense hsp6 5II-1 might represent an additional subspecies of M. massiliense.

Genome analysis reveals three genomospecies in Mycobacterium abscessus

Background

Mycobacterium abscessus complex, the third most frequent mycobacterial complex responsible for community- and health care-associated infections in developed countries, comprises of M. abscessus subsp. abscessus and M. abscessus subsp. bolletii reviously referred as Mycobacterium bolletii and Mycobacterium massiliense. The diversity of this group of opportunistic pathogens is poorly described.

Results

In-depth analysis of 14 published M. abscessus complex genomes found a pan-genome of 6,153 proteins and core-genome of 3,947 (64.1%) proteins, indicating a non-conservative genome. Analysing the average percentage of amino-acid sequence identity (from 94.19% to 98.58%) discriminates three main clusters C1, C2 and C3: C1 comprises strains belonging to M. abscessus, C2 comprises strains belonging to M. massiliense and C3 comprises strains belonging to M. bolletii; and two sub-clusters in clusters C2 and C3. The phylogenomic network confirms these three clusters. The genome length (from 4.8 to 5.51-Mb) varies from 5.07-Mb in C1, 4.89-Mb in C2A, 5.01-Mb in C2B and 5.28-Mb in C3. The mean number of prophage regions (from 0 to 7) is 2 in C1; 1.33 in C2A; 3.5 in C2B and five in C3. A total of 36 genes are uniquely present in C1, 15 in C2 and 15 in C3. These genes could be used for the detection and identification of organisms in each cluster. Further, the mean number of host-interaction factors (including PE, PPE, LpqH, MCE, Yrbe and type VII secretion system ESX3 and ESX4) varies from 70 in cluster C1, 80 in cluster C2A, 74 in cluster C2B and 93 in clusters C3A and C3B. No significant differences in antibiotic resistance genes were observed between clusters, in contrast to previously reported in-vitro patterns of drug resistance. They encode both penicillin-binding proteins targeted by β-lactam antibiotics and an Ambler class A β-lactamase for which inhibitors exist.

Conclusions

Our comparative analysis indicates that M. abscessus complex comprises three genomospecies, corresponding to M. abscessus, M. bolletii, and M. massiliense. The genomics data here reported indicate differences in virulence of medical interest; and suggest targets for the refined detection and identification of M. abscessus.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-359) contains supplementary material, which is available to authorized users.

Lack of antimicrobial bactericidal activity in Mycobacterium abscessus

Antibiotic therapy of infections caused by the emerging pathogen Mycobacterium abscessus is challenging due to the organism's natural resistance toward most clinically available antimicrobials. We investigated the bactericidal activity of antibiotics commonly administered in M. abscessus infections in order to better understand the poor therapeutic outcome. Time-kill curves were generated for clinical M. abscessus isolates, Mycobacterium smegmatis, and Escherichia coli by using antibiotics commonly categorized as bactericidal (amikacin and moxifloxacin) or bacteriostatic (tigecycline and linezolid). In addition, the impact of aminoglycoside-modifying enzymes on the mode of action of substrate and nonsubstrate aminoglycosides was studied by using M. smegmatis as a model organism. While amikacin and moxifloxacin were bactericidal against E. coli, none of the tested compounds showed bactericidal activity against M. abscessus. Further mechanistic investigations of the mode of action of aminoglycosides in M. smegmatis revealed that the bactericidal activity of tobramycin and gentamicin was restored by disruption of the chromosomal aac(2') gene in the mycobacterial genome. The lack of bactericidal antibiotics in currently recommended treatment regimens provides a reasonable explanation for the poor therapeutic outcome in M. abscessus infection. Our findings suggest that chromosomally encoded drug-modifying enzymes play an important role in the lack of aminoglycoside bactericidal activity against rapidly growing mycobacteria.

Gene replacement in Mycobacterium chelonae: application to the construction of porin knock-out mutants

Mycobacterium chelonae is a rapidly growing mycobacterial opportunistic pathogen closely related to Mycobacterium abscessus that causes cornea, skin and soft tissue infections in humans. Although M. chelonae and the emerging mycobacterial pathogen M. abscessus have long been considered to belong to the same species, these two microorganisms considerably differ in terms of optimum growth temperature, drug susceptibility, pathogenicity and the types of infection they cause. The whole genome sequencing of clinical isolates of M. chelonae and M. abscessus is opening the way to comparative studies aimed at understanding the biology of these pathogens and elucidating the molecular bases of their pathogenicity and biocide resistance. Key to the validation of the numerous hypotheses that this approach will raise, however, is the availability of genetic tools allowing for the expression and targeted mutagenesis of genes in these species. While homologous recombination systems have recently been described for M. abscessus, genetic tools are lacking for M. chelonae. We here show that two different allelic replacement methods, one based on mycobacteriophage-encoded recombinases and the other on a temperature-sensitive plasmid harboring the counterselectable marker sacB, can be used to efficiently disrupt genes in this species. Knock-out mutants for each of the three porin genes of M. chelonae ATCC 35752 were constructed using both methodologies, one of which displays a significantly reduced glucose uptake rate consistent with decreased porin expression.

Prophage-like elements present in Mycobacterium genomes

Background

Prophages, integral components of many bacterial genomes, play significant roles in cognate host bacteria, such as virulence, toxin biosynthesis and secretion, fitness cost, genomic variations, and evolution. Many prophages and prophage-like elements present in sequenced bacterial genomes, such as Bifidobacteria, Lactococcus and Streptococcus, have been described. However, information for the prophage of Mycobacterium remains poorly defined.

Results

In this study, based on the search of the complete genome database from GenBank, the Whole Genome Shotgun (WGS) databases, and some published literatures, thirty-three prophages were described in detail. Eleven of them were full-length prophages, and others were prophage-like elements. Eleven prophages were firstly revealed. They were phiMAV_1, phiMAV_2, phiMmcs_1, phiMmcs_2, phiMkms_1, phiMkms_2, phiBN42_1, phiBN44_1, phiMCAN_1, phiMycsm_1, and phiW7S_1. Their genomes and gene contents were firstly analyzed. Furthermore, comparative genomics analyses among mycobacterioprophages showed that full-length prophage phi172_2 belonged to mycobacteriophage Cluster A and the phiMmcs_1, phiMkms_1, phiBN44_1, and phiMCAN_1 shared high homology and could be classified into one group.

Conclusions

To our knowledge, this is the first systematic characterization of mycobacterioprophages, their genomic organization and phylogeny. This information will afford more understanding of the biology of Mycobacterium.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-243) contains supplementary material, which is available to authorized users.

Demonstration of plasmid-mediated drug resistance in Mycobacterium abscessus

Plasmid-mediated kanamycin resistance was detected in a strain of Mycobacterium abscessus subsp. bolletii responsible for a nationwide epidemic of surgical infections in Brazil. The plasmid did not influence susceptibility to tobramycin, streptomycin, trimethoprim-sulfamethoxazole, clarithromycin, or ciprofloxacin. Plasmid-mediated drug resistance has not been described so far in mycobacteria.

Mycobacterium abscessus cording prevents phagocytosis and promotes abscess formation

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.

Novel drug combination for Mycobacterium abscessus disease therapy identified in a Drosophila infection model

OBJECTIVES

Mycobacterium abscessus is known to be the most drug-resistant Mycobacterium and accounts for ∼80% of pulmonary infections caused by rapidly growing mycobacteria. This study reports a new Drosophila melanogaster-M. abscessus infection model that can be used as an in vivo efficacy model for anti-M. abscessus drug potency assessment.

METHODS

D. melanogaster were challenged with M. abscessus, and infected flies were fed with a fly medium containing tigecycline, clarithromycin, linezolid, clofazimine, moxifloxacin, amikacin, cefoxitin, dinitrobenzamide or metronidazole at different concentrations (0, 100 and 500 mg/L). The survival rates of infected flies were plotted and bacterial colonization/dissemination in fly bodies was monitored by cfu determination and green fluorescent protein epifluorescence.

RESULTS

The D. melanogaster-M. abscessus model enabled an assessment of the effectiveness of antibiotic treatment. Tigecycline was the best drug for extending the lifespan of M. abscessus-infected Drosophila, followed by clarithromycin and linezolid. Several different combinations of tigecycline, linezolid and clarithromycin were tested to determine the best combination. Tigecycline (25 mg/L) plus linezolid (500 mg/L) was the best drug combination and its efficacy was superior to conventional regimens, not only in prolonging infected fly survival but also against M. abscessus colonization and dissemination.

CONCLUSIONS

This D. melanogaster-M. abscessus infection/curing methodology may be useful for the rapid evaluation of potential drug candidates. In addition, new combinations using tigecycline and linezolid should be considered as possible next-generation combination therapies to be assessed in higher organisms.

A global virulence regulator in Acinetobacter baumannii and its control of the phenylacetic acid catabolic pathway

BACKGROUND

Acinetobacter baumannii is one of the most notorious hospital-acquired pathogens, and novel treatment strategies are desperately required. Two-component regulatory systems represent potential therapeutic targets as they mediate microorganism adaptation to changing environments, often control virulence, and are specific to bacteria. Here we describe the first global virulence regulator in A. baumannii.

METHODS AND RESULTS

Using transcriptional profiling and functional assays of a deletion mutant in the A. baumannii sensor kinase gene, A1S_0574 (termed as gacS), we show that this sensor kinase regulates key virulence characteristics, including pili synthesis, biofilms, and motility, resulting in virulence attenuation in a mammalian septicemia model. Notably, we also identified that GacS regulates an operon novel to A. baumannii (paa operon), which is responsible for the metabolism of aromatic compounds. Deletion of paaE (A1S_1340) confirmed the role of this operon in A. baumannii virulence. Finally, we identified the cognate response regulator (A1S_0236) for GacS and confirmed their interaction. A1S_0236 was shown to regulate 75% of the GacS transcriptome and the same virulence phenotypes. Overexpression of A1S_0236 restored virulence in the gacS mutant.

CONCLUSIONS

Our study characterizes a global virulence regulator, which may provide an alternate therapeutic target, in one of the most troublesome hospital-acquired pathogens.

atpE gene as a new useful specific molecular target to quantify Mycobacterium in environmental samples

Background

The environment is the likely source of many pathogenic mycobacterial species but detection of mycobacteria by bacteriological tools is generally difficult and time-consuming. Consequently, several molecular targets based on the sequences of housekeeping genes, non-functional RNA and structural ribosomal RNAs have been proposed for the detection and identification of mycobacteria in clinical or environmental samples. While certain of these targets were proposed as specific for this genus, most are prone to false positive results in complex environmental samples that include related, but distinct, bacterial genera. Nowadays the increased number of sequenced genomes and the availability of software for genomic comparison provide tools to develop novel, mycobacteria-specific targets, and the associated molecular probes and primers. Consequently, we conducted an in silico search for proteins exclusive to Mycobacterium spp. genomes in order to design sensitive and specific molecular targets.

Results

Among the 3989 predicted proteins from M. tuberculosis H37Rv, only 11 proteins showed 80% to 100% of similarity with Mycobacterium spp. genomes, and less than 50% of similarity with genomes of closely related Corynebacterium, Nocardia and Rhodococcus genera. Based on DNA sequence alignments, we designed primer pairs and a probe that specifically detect the atpE gene of mycobacteria, as verified by quantitative real-time PCR on a collection of mycobacteria and non-mycobacterial species. The real-time PCR method we developed was successfully used to detect mycobacteria in tap water and lake samples.

Conclusions

The results indicate that this real-time PCR method targeting the atpE gene can serve for highly specific detection and precise quantification of Mycobacterium spp. in environmental samples.

The genome sequence of 'Mycobacterium massiliense' strain CIP 108297 suggests the independent taxonomic status of the Mycobacterium abscessus complex at the subspecies level

Members of the Mycobacterium abscessus complex are rapidly growing mycobacteria that are emerging as human pathogens. The M. abscessus complex was previously composed of three species, namely M. abscessus sensu stricto, 'M. massiliense', and 'M. bolletii'. In 2011, 'M. massiliense' and 'M. bolletii' were united and reclassified as a single subspecies within M. abscessus: M. abscessus subsp. bolletii. However, the placement of 'M. massiliense' within the boundary of M. abscessus subsp. bolletii remains highly controversial with regard to clinical aspects. In this study, we revisited the taxonomic status of members of the M. abscessus complex based on comparative analysis of the whole-genome sequences of 53 strains. The genome sequence of the previous type strain of 'Mycobacterium massiliense' (CIP 108297) was determined using next-generation sequencing. The genome tree based on average nucleotide identity (ANI) values supported the differentiation of 'M. bolletii' and 'M. massiliense' at the subspecies level. The genome tree also clearly illustrated that 'M. bolletii' and 'M. massiliense' form a distinct phylogenetic clade within the radiation of the M. abscessus complex. The genomic distances observed in this study suggest that the current M. abscessus subsp. bolletii taxon should be divided into two subspecies, M. abscessus subsp. massiliense subsp. nov. and M. abscessus subsp. bolletii, to correspondingly accommodate the previously known 'M. massiliense' and 'M. bolletii' strains.

Characterization of broad-spectrum Mycobacterium abscessus class A β-lactamase

OBJECTIVES

Imipenem and cefoxitin are used to treat Mycobacterium abscessus infections and have moderate activity against this fast-growing mycobacterium (MIC₅₀ of 16 and 32 mg/L, respectively). M. abscessus is highly resistant to most other β-lactams, although the underlying mechanisms have not been explored. Here, we characterized M. abscessus class A β-lactamase (Bla(Mab)) and investigated its role in β-lactam resistance.

METHODS

Hydrolysis kinetic parameters of purified Bla(Mab) were determined by spectrophotometry for various β-lactams and compared with those of related BlaC from Mycobacterium tuberculosis. MICs of β-lactams were determined for M. abscessus CIP104536 and for Escherichia coli producing Bla(Mab) and BlaC.

RESULTS

Bla(Mab) had a broad hydrolysis spectrum, similar to that of BlaC, but with overall higher catalytic efficiencies, except for cefoxitin. As expected from its in vivo efficacy, cefoxitin was very slowly hydrolysed by Bla(Mab) (k(cat)/K(m) = 6.7 M(-1) s(-1)). Bla(Mab) hydrolysed imipenem more efficiently (k(cat)/K(m) = 3.0 × 10(4) M(-1) s(-1)), indicating that the in vivo activity of this drug might be improved by combination with a β-lactamase inhibitor. β-Lactamase inhibitors clavulanate, tazobactam and sulbactam did not inhibit Bla(Mab). This enzyme efficiently hydrolysed clavulanate, in contrast to BlaC, which is irreversibly acylated by this inhibitor. Bla(Mab) and BlaC were functional in E. coli and the resistance profiles mediated by these enzymes were in agreement with the kinetic parameters.

CONCLUSIONS

M. abscessus produces a clavulanate-insensitive broad-spectrum β-lactamase that limits the in vivo efficacy of β-lactams.

Phylogenomics of Brazilian epidemic isolates of Mycobacterium abscessus subsp. bolletii reveals relationships of global outbreak strains

Rapidly growing, non-tuberculous mycobacteria (NTM) in the Mycobacterium abscessus (MAB) species are emerging pathogens that cause various diseases including skin and respiratory infections. The species has undergone recent taxonomic nomenclature refinement, and is currently recognized as two subspecies, M. abscessus subsp. abscessus (MAB-A) and M. abscessus subsp. bolletii (MAB-B). The recently reported outbreaks of MAB-B in surgical patients in Brazil from 2004 to 2009 and in cystic fibrosis patients in the United Kingdom (UK) in 2006 to 2012 underscore the need to investigate the genetic diversity of clinical MAB strains. To this end, we sequenced the genomes of two Brazilian MAB-B epidemic isolates (CRM-0019 and CRM-0020) derived from an outbreak of skin infections in Rio de Janeiro, two unrelated MAB strains from patients with pulmonary infections in the United States (US) (NJH8 and NJH11) and one type MAB-B strain (CCUG 48898) and compared them to 25 publically available genomes of globally diverse MAB strains. Genome-wide analyses of 27,598 core genome single nucleotide polymorphisms (SNPs) revealed that the two Brazilian derived CRM strains are nearly indistinguishable from one another and are more closely related to UK outbreak isolates infecting CF patients than to strains from the US, Malaysia or France. Comparative genomic analyses of six closely related outbreak strains revealed geographic-specific large-scale insertion/deletion variation that corresponds to bacteriophage insertions and recombination hotspots. Our study integrates new genome sequence data with existing genomic information to explore the global diversity of infectious M. abscessus isolates and to compare clinically relevant outbreak strains from different continents.

Identification and characterization of the genetic changes responsible for the characteristic smooth-to-rough morphotype alterations of clinically persistent Mycobacterium abscessus

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.

Insertion site and distribution of a genomic island conferring DNA phosphorothioation in the Mycobacterium abscessus complex

Nearly half of US clinical isolates of the emerging pathogen Mycobacterium abscessus were reported to exhibit smeared DNA during PFGE. This DNA degradation (Dnd) phenotype results from DNA phosphorothioation, a sulfur modification found in other bacteria and conferred by dnd genes located on mobile elements. Putative dnd genes are located on a 19.6 kbp genomic island (GI) in the M. abscessus type strain ATCC 19977. We confirmed that ATCC 19977(T) is Dnd-positive by PFGE and we developed a PCR assay to predict Dnd phenotype. Dnd-positive strains generated an amplicon from dndC whereas Dnd-negative strains generated a bridge amplicon that spanned the GI insertion site, indicating they lacked the entire 'Dnd-GI'. Comparative analyses of sequences from the bridge amplicon with ATCC 19977(T) revealed the Dnd-GI is flanked by 22 bp repeats in M. abscessus sensu stricto and inserted downstream of a tRNA-Ala gene and between inverted repeats. Regions flanking the Dnd-GI were highly conserved within the M. abscessus complex. Bioinformatics studies suggest the Dnd-GI inserted independently into a strain of Mycobacterium massiliense and that other species of mycobacteria also have dnd genes, supporting reports that the Dnd phenotype is common among actinomycetes. Within the M. abscessus complex, Dnd-positive clinical isolates were primarily M. abscessus sensu stricto, and tandem repeat typing indicated these isolates were highly related, confirming previous PFGE studies and revealing a widespread family of strains with significance in human disease.

Whole-Genome Sequence of Mycobacterium abscessus Clinical Strain V06705

Infection caused by Mycobacterium abscessus strains is a growing cause of concern in both community-acquired and health care-associated diseases, as these organisms naturally display multiple drug resistances. We report an annotated draft genome sequence of M. abscessus strain V06705 obtained from a patient in France.

Genome Sequence of an Epidemic Isolate of Mycobacterium abscessus subsp. bolletii from Rio de Janeiro, Brazil

Multiple isolates of Mycobacterium abscessus subsp. bolletii, collectively called BRA100, were associated with outbreaks of postsurgical skin infections across various regions of Brazil from 2003 to 2009. We announce the draft genome sequence of a newly sequenced BRA100 strain, M. abscessus subsp. bolletii CRM-0020, isolated from a patient in Rio de Janeiro, Brazil.

Mab_3168c, a putative acetyltransferase, enhances adherence, intracellular survival and antimicrobial resistance of Mycobacterium abscessus

Mycobacterium abscessus is a non-tuberculous mycobacterium. It can cause diseases in both immunosuppressed and immunocompetent patients and is highly resistant to multiple antimicrobial agents. M. abscessus displays two different colony morphology types: smooth and rough morphotypes. Cells with a rough morphotype are more virulent. The purpose of this study was to identify genes responsible for M. abscessus morphotype switching. With transposon mutagenesis, a mutant with a Tn5 inserted into the promoter region of the mab_3168c gene was found to switch its colonies from a rough to a smooth morphotype. This mutant had a higher sliding motility but a lower ability to form biofilms, aggregate in culture, and survive inside macrophages. Results of bioinformatic analyses suggest that the putative Mab_3168c protein is a member of the GCN5-related N-acetyltransferase superfamily. This prediction was supported by the demonstration that the mab_3168c gene conferred M. abscessus and M. smegmatis cells resistance to amikacin. The multiple roles of mab_3168c suggest that it could be a potential target for development of therapeutic regimens to treat diseases caused by M. abscessus.

Pulmonary disease caused by nontuberculous mycobacteria

The propensity of various nontuberculous mycobacteria to cause lung disease varies widely and is conditioned by host factors; infection is believed to occur from environmental sources. Nontuberculous mycobacteria pulmonary disease (PNTM) is increasing worldwide and Mycobacterium avium complex is the most common cause. PNTM usually occurs in one of three prototypical forms: hypersensitivity pneumonitis, cavitary tuberculosis-like disease or nodular bronchiectasis. PNTM has been linked in some patients to genetic variants of the cystic fibrosis transmembrane conductance regulator gene and a distinct patient phenotype. Interactions between PNTM and other comorbidities are also increasingly appreciated. Guidelines for diagnosis, emphasizing chest imaging and microbiology, have been published; speciation using molecular techniques is critical for accuracy and for treatment decisions. Clinical trials are lacking to inform treatment for many species and experience with M. avium complex and several others species serves as a guide instead. Use of multiple drugs for a period of at least 12 months following sputum conversion is the norm for most species. In vitro drug susceptibility results for many drugs may not correlate with clinical outcomes and such testing should be done on a selective basis.

Whole-genome sequencing to identify transmission of Mycobacterium abscessus between patients with cystic fibrosis: a retrospective cohort study

BACKGROUND

Increasing numbers of individuals with cystic fibrosis are becoming infected with the multidrug-resistant non-tuberculous mycobacterium (NTM) Mycobacterium abscessus, which causes progressive lung damage and is extremely challenging to treat. How this organism is acquired is not currently known, but there is growing concern that person-to-person transmission could occur. We aimed to define the mechanisms of acquisition of M abscessus in individuals with cystic fibrosis.

METHOD

Whole genome sequencing and antimicrobial susceptibility testing were done on 168 consecutive isolates of M abscessus from 31 patients attending an adult cystic fibrosis centre in the UK between 2007 and 2011. In parallel, we undertook detailed environmental testing for NTM and defined potential opportunities for transmission between patients both in and out of hospital using epidemiological data and social network analysis.

FINDINGS

Phylogenetic analysis revealed two clustered outbreaks of near-identical isolates of the M abscessus subspecies massiliense (from 11 patients), differing by less than ten base pairs. This variation represents less diversity than that seen within isolates from a single individual, strongly indicating between-patient transmission. All patients within these clusters had numerous opportunities for within-hospital transmission from other individuals, while comprehensive environmental sampling, initiated during the outbreak, failed to detect any potential point source of NTM infection. The clusters of M abscessus subspecies massiliense showed evidence of transmission of mutations acquired during infection of an individual to other patients. Thus, isolates with constitutive resistance to amikacin and clarithromycin were isolated from several individuals never previously exposed to long-term macrolides or aminoglycosides, further indicating cross-infection.

INTERPRETATION

Whole genome sequencing has revealed frequent transmission of multidrug resistant NTM between patients with cystic fibrosis despite conventional cross-infection measures. Although the exact transmission route is yet to be established, our epidemiological analysis suggests that it could be indirect.

FUNDING

The Wellcome Trust, Papworth Hospital, NIHR Cambridge Biomedical Research Centre, UK Health Protection Agency, Medical Research Council, and the UKCRC Translational Infection Research Initiative.

MabsBase: a Mycobacterium abscessus genome and annotation database

Mycobacterium abscessus is a rapidly growing non-tuberculous mycobacterial species that has been associated with a wide spectrum of human infections. As the classification and biology of this organism is still not well understood, comparative genomic analysis on members of this species may provide further insights on their taxonomy, phylogeny, pathogenicity and other information that may contribute to better management of infections. The MabsBase described in this paper is a user-friendly database providing access to whole-genome sequences of newly discovered M. abscessus strains as well as resources for whole-genome annotations and computational predictions, to support the expanding scientific community interested in M. abscessus research. The MabsBase is freely available at http://mabscessus.um.edu.my.

The detection and sequencing of a broad-host-range conjugative IncP-1β plasmid in an epidemic strain of Mycobacterium abscessus subsp. bolletii

BACKGROUND

An extended outbreak of mycobacterial surgical infections occurred in Brazil during 2004-2008. Most infections were caused by a single strain of Mycobacterium abscessus subsp. bolletii, which was characterized by a specific rpoB sequevar and two highly similar pulsed-field gel electrophoresis (PFGE) patterns differentiated by the presence of a ∼50 kb band. The nature of this band was investigated.

METHODOLOGY/PRINCIPAL FINDINGS

Genomic sequencing of the prototype outbreak isolate INCQS 00594 using the SOLiD platform demonstrated the presence of a 56,267-bp [corrected] circular plasmid, designated pMAB01. Identity matrices, genetic distances and phylogeny analyses indicated that pMAB01 belongs to the broad-host-range plasmid subgroup IncP-1β and is highly related to BRA100, pJP4, pAKD33 and pB10. The presence of pMAB01-derived sequences in 41 M. abscessus subsp. bolletii isolates was evaluated using PCR, PFGE and Southern blot hybridization. Sixteen of the 41 isolates showed the presence of the plasmid. The plasmid was visualized as a ∼50-kb band using PFGE and Southern blot hybridization in 12 isolates. The remaining 25 isolates did not exhibit any evidence of this plasmid. The plasmid was successfully transferred to Escherichia coli by conjugation and transformation. Lateral transfer of pMAB01 to the high efficient plasmid transformation strain Mycobacterium smegmatis mc(2)155 could not be demonstrated.

CONCLUSIONS/SIGNIFICANCE

The occurrence of a broad-host-range IncP-1β plasmid in mycobacteria is reported for the first time. Thus, genetic exchange could result in the emergence of specific strains that might be better adapted to cause human disease.

Mycobacterial genotypes are associated with clinical manifestation and progression of lung disease caused by Mycobacterium abscessus and Mycobacterium massiliense

BACKGROUND

Mycobacterium abscessus and Mycobacterium massiliense, which cause lung disease, are variable in their clinical manifestation and progression. We hypothesized that mycobacterial genotypes represent their pathogenic phenotypes, which would result in particular genotypes being associated with disease progression.

METHODS

Variable number tandem repeat (VNTR) loci were selected to establish a genotype assay that was capable of differentiating patients with heterogeneous prognoses in the development cohort (48 isolates). The analysis was reevaluated in the validation cohort (63 isolates).

RESULTS

A total of 53 M. abscessus and 58 M. massiliense isolates were assembled into 3 clusters based on their VNTR genotyping. The patients in cluster A were more likely to have stable disease of the nodular bronchiectatic form; 100% of M. abscessus patients and 96% of M. massiliense patients were followed without antibiotic treatment for >24 months after diagnosis. In contrast, the patients in cluster B were more likely to have progressive disease of the nodular bronchiectatic form; 96% of M. abscessus patients and 81% of M. massiliense patients started antibiotic treatment within 24 months after diagnosis. All patients in cluster C had fibrocavitary disease and started antibiotic treatment immediately after diagnosis. The genetic distance of each clinical isolate from the reference strain was associated with the highest likelihood of disease progression and a disease phenotype of the fibrocavitary form (P < .001).

CONCLUSIONS

Mycobacterial genotyping of M. abscessus and M. massiliense may provide valuable information for predicting disease phenotype and progression.

Identification and characterization of potential therapeutic candidates in emerging human pathogen Mycobacterium abscessus: a novel hierarchical in silico approach

Mycobacterium abscessus, a non-tuberculous rapidly growing mycobacterium, is recognized as an emerging human pathogen causing a variety of infections ranging from skin and soft tissue infections to severe pulmonary infections. Lack of an optimal treatment regimen and emergence of multi-drug resistance in clinical isolates necessitate the development of better/new drugs against this pathogen. The present study aims at identification and qualitative characterization of promising drug targets in M. abscessus using a novel hierarchical in silico approach, encompassing three phases of analyses. In phase I, five sets of proteins were mined through chokepoint, plasmid, pathway, virulence factors, and resistance genes and protein network analysis. These were filtered in phase II, in order to find out promising drug target candidates through subtractive channel of analysis. The analysis resulted in 40 therapeutic candidates which are likely to be essential for the survival of the pathogen and non-homologous to host, human anti-targets, and gut flora. Many of the identified targets were found to be involved in different metabolisms (viz., amino acid, energy, carbohydrate, fatty acid, and nucleotide), xenobiotics degradation, and bacterial pathogenicity. Finally, in phase III, the candidate targets were qualitatively characterized through cellular localization, broad spectrum, interactome, functionality, and druggability analysis. The study explained their subcellular location identifying drug/vaccine targets, possibility of being broad spectrum target candidate, functional association with metabolically interacting proteins, cellular function (if hypothetical), and finally, druggable property. Outcome of the present study could facilitate the identification of novel antibacterial agents for better treatment of M. abscesses infections.

Whole-Genome Shotgun Sequencing of Mycobacterium abscessus M156, an Emerging Clinical Pathogen in Malaysia

Mycobacterium abscessus is an emerging clinical pathogen commonly associated with non-tuberculous mycobacterial infections. We report herein the draft genome of M. abscessus strain M156.

Antimicrobial efflux pumps and Mycobacterium tuberculosis drug tolerance: evolutionary considerations

The need for lengthy treatment to cure tuberculosis stems from phenotypic drug resistance, also known as drug tolerance, which has been previously attributed to slowed bacterial growth in vivo. We discuss recent findings that challenge this model and instead implicate macrophage-induced mycobacterial efflux pumps in antimicrobial tolerance. Although mycobacterial efflux pumps may have originally served to protect against environmental toxins, in the pathogenic mycobacteria, they appear to have been repurposed for intracellular growth. In this light, we discuss the potential of efflux pump inhibitors such as verapamil to shorten tuberculosis treatment by their dual inhibition of tolerance and growth.

Analysis of the genome of Mycobacterium abscessus strain M94 reveals an uncommon cluster of tRNAs

Mycobacterium abscessus is a species of rapidly growing nontuberculous mycobacteria that is frequently associated with opportunistic infections in humans. Here, we report the annotated genome sequence of M. abscessus strain M94, which showed an unusual cluster of tRNAs.

Comparative genomic and phylogenetic approaches to characterize the role of genetic recombination in mycobacterial evolution

The genus Mycobacterium encompasses over one hundred named species of environmental and pathogenic organisms, including the causative agents of devastating human diseases such as tuberculosis and leprosy. The success of these human pathogens is due in part to their ability to rapidly adapt to their changing environment and host. Recombination is the fastest way for bacterial genomes to acquire genetic material, but conflicting results about the extent of recombination in the genus Mycobacterium have been reported. We examined a data set comprising 18 distinct strains from 13 named species for evidence of recombination. Genomic regions common to all strains (accounting for 10% to 22% of the full genomes of all examined species) were aligned and concatenated in the chromosomal order of one mycobacterial reference species. The concatenated sequence was screened for evidence of recombination using a variety of statistical methods, with each proposed event evaluated by comparing maximum-likelihood phylogenies of the recombinant section with the non-recombinant portion of the dataset. Incongruent phylogenies were identified by comparing the site-wise log-likelihoods of each tree using multiple tests. We also used a phylogenomic approach to identify genes that may have been acquired through horizontal transfer from non-mycobacterial sources. The most frequent associated lineages (and potential gene transfer partners) in the Mycobacterium lineage-restricted gene trees are other members of suborder Corynebacterinae, but more-distant partners were identified as well. In two examined cases of potentially frequent and habitat-directed transfer (M. abscessus to Segniliparus and M. smegmatis to Streptomyces), observed sequence distances were small and consistent with a hypothesis of transfer, while in a third case (M. vanbaalenii to Streptomyces) distances were larger. The analyses described here indicate that whereas evidence of recombination in core regions within the genus is relatively sparse, the acquisition of genes from non-mycobacterial lineages is a significant feature of mycobacterial evolution.

Genomic insights into the emerging human pathogen Mycobacterium massiliense

Mycobacterium massiliense (Mycobacterium abscessus group) is an emerging pathogen causing pulmonary disease and skin and soft tissue infections. We report the genome sequence of the type strain CCUG 48898.