Mycobacterium abscessus infection in cystic fibrosis. Colonization or infection?

Impact of IL-1β on lung pathology caused by Mycobacterium abscessus infection and its association with IL-17 production

Mycobacterium abscessus (MAB), a non-tuberculous mycobacterium (NTM), causes chronic pulmonary inflammation in humans. The NLRP3 inflammasome is a multi-protein complex that triggers IL-1β maturation and pyroptosis through the cleavage of caspase-1. In this study, we investigated the roles of NLRP3 and IL-1β in the host's defense against MAB. The IL-1β production by MAB was completely abolished in NLRP3, but not NLRC4, deficient macrophages. The NLRP3 inflammasome components, which are ASC and caspase-1 were also found to be essential for IL-1β production in response to MAB. NLRP3 and IL-1β deficiency did not affect the intracellular growth of MAB in macrophages, and the bacterial burden in lungs of NLRP3- and IL-1β-deficient mice was also comparable to the burden observed in WT mice. In contrast, IL-1β deficiency ameliorated lung pathology in MAB-infected mice. Notably, the lung homogenates of IL-1β-deficient mice had reduced levels of IL-17, but not IFN-γ and IL-4 when compared with WT counterparts. Furthermore, in vitro co-culture analysis showed that IL-1β signaling was essential for IL-17 production in response to MAB. Finally, we observed that the anti-IL-17 antibody administration moderately mitigated MAB-induced lung pathology. These findings indicated that IL-1β production contribute to MAB-induced lung pathology via the elevation of IL-17 production.

Mycobacterium abscessus: It’s Complex

Mycobacterium abscessus (M. abscessus) is an opportunistic pathogen usually colonizing abnormal lung airways and is often seen in patients with cystic fibrosis. Currently, there is no vaccine available for M. abscessus in clinical development. The treatment of M. abscessus-related pulmonary diseases is peculiar due to intrinsic resistance to several commonly used antibiotics. The development of either prophylactic or therapeutic interventions for M. abscessus pulmonary infections is hindered by the absence of an adequate experimental animal model. In this review, we outline the critical elements related to M. abscessus virulence mechanisms, host–pathogen interactions, and treatment challenges associated with M. abscessus pulmonary infections. The challenges of effectively combating this pathogen include developing appropriate preclinical animal models of infection, developing proper diagnostics, and designing novel strategies for treating drug-resistant M. abscessus.

Therapeutic efficacy of antimalarial drugs targeting DosRS signaling in Mycobacterium abscessus

A search for alternative Mycobacterium abscessus treatments led to our interest in the two-component regulator DosRS, which, in Mycobacterium tuberculosis, is required for the bacterium to establish a state of nonreplicating, drug-tolerant persistence in response to a variety of host stresses. We show here that the genetic disruption of dosRS impairs the adaptation of M. abscessus to hypoxia, resulting in decreased bacterial survival after oxygen depletion, reduced tolerance to a number of antibiotics in vitro and in vivo, and the inhibition of biofilm formation. We determined that three antimalarial drugs or drug candidates, artemisinin, OZ277, and OZ439, can target DosS-mediated hypoxic signaling in M. abscessus and recapitulate the phenotypic effects of genetically disrupting dosS. OZ439 displayed bactericidal activity comparable to standard-of-care antibiotics in chronically infected mice, in addition to potentiating the activity of antibiotics used in combination. The identification of antimalarial drugs as potent inhibitors and adjunct inhibitors of M. abscessus in vivo offers repurposing opportunities that could have an immediate impact in the clinic.

Variability in the Management of Adults With Pulmonary Nontuberculous Mycobacterial Disease

BACKGROUND

The increasing global prevalence of pulmonary nontuberculous mycobacteria (NTM) disease has called attention to challenges in NTM diagnosis and management. This study was conducted to understand management and outcomes of patients with pulmonary NTM disease at diverse centers across the United States.

METHODS

We conducted a 10-year (2005-2015) retrospective study at 7 Vaccine and Treatment Evaluation Units to evaluate pulmonary NTM treatment outcomes in human immunodeficiency virus-negative adults. Demographic and clinical information was abstracted through medical record review. Microbiologic and clinical cure were evaluated using previously defined criteria.

RESULTS

Of 297 patients diagnosed with pulmonary NTM, the most frequent NTM species were Mycobacterium avium-intracellulare complex (83.2%), M. kansasii (7.7%), and M. abscessus (3.4%). Two hundred forty-five (82.5%) patients received treatment, while 45 (15.2%) were followed without treatment. Eighty-six patients had available drug susceptibility results; of these, >40% exhibited resistance to rifampin, ethambutol, or amikacin. Of the 138 patients with adequate outcome data, 78 (56.5%) experienced clinical and/or microbiologic cure. Adherence to the American Thoracic Society/Infectious Diseases Society of America (ATS/IDSA) treatment guidelines was significantly more common in patients who were cured (odds ratio, 4.5, 95% confidence interval, 2.0-10.4; P < .001). Overall mortality was 15.7%.

CONCLUSIONS

Despite ATS/IDSA Guidelines, management of pulmonary NTM disease was heterogeneous and cure rates were relatively low. Further work is required to understand which patients are suitable for monitoring without treatment and the impact of antimicrobial therapy on pulmonary NTM morbidity and mortality.

A bird eye view on cystic fibrosis: An underestimated multifaceted chronic disorder

Cystic fibrosis (CF) is an autosomal recessive disease which involves the mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. CF involves in the inflammatory processes and is considered as a multisystem disorder that is not confined to lungs, but it also affects other vital organs that leads to numerous co-morbidities. The respiratory disorder in the CF results in mortality and morbidity which is characterized by series of serious events involving mucus hypersecretion, microbial infections, airways obstruction, inflammation, destruction of epithelium, tissue remodeling and terminal lung diseases. Mucins are the high molecular weight glycoproteins important for the viscoelastic properties of the mucus, play a significant role in the disease mechanisms. Determining the functional association between the CFTR and mucins might help to identify the putative target for specific therapeutic approach. In fact, furin enzyme which helps in the entry of novel COVID-19 virus into the cell, is upregulated in CF and this can also serve as a potential target for CF treatment. Moreover, the use of nano-formulations for CF treatment is an area of research being widely studied as they have also demonstrated promising outcomes. The in-depth knowledge of non-coding RNAs like miRNAs and lncRNAs and their functional association with CFTR gene expression and mutation can provide a different range of opportunity to identify the promising therapeutic approaches for CF.

Ex vivo infection of murine precision-cut lung tissue slices with Mycobacterium abscessus: a model to study antimycobacterial agents

Background

Multidrug-resistant infections due to Mycobacterium abscessus often require complex and prolonged regimens for treatment. Here, we report the evaluation of a new ex vivo antimicrobial susceptibility testing model using organotypic cultures of murine precision-cut lung slices, an experimental model in which metabolic activity, and all the usual cell types of the organ are found while the tissue architecture and the interactions between the different cells are maintained.

Methods

Precision cut lung slices (PCLS) were prepared from the lungs of wild type BALB/c mice using the Krumdieck^® tissue slicer. Lung tissue slices were ex vivo infected with the virulent M. abscessus strain L948. Then, we tested the antimicrobial activity of two drugs: imipenem (4, 16 and 64 μg/mL) and tigecycline (0.25, 1 and 4 μg/mL), at 12, 24 and 48 h. Afterwards, CFUs were determined plating on blood agar to measure the surviving intracellular bacteria. The viability of PCLS was assessed by Alamar Blue assay and corroborated using histopathological analysis.

Results

PCLS were successfully infected with a virulent strain of M. abscessus as demonstrated by CFUs and detailed histopathological analysis. The time-course infection, including tissue damage, parallels in vivo findings reported in genetically modified murine models for M. abscessus infection. Tigecycline showed a bactericidal effect at 48 h that achieved a reduction of > 4log₁₀ CFU/mL against the intracellular mycobacteria, while imipenem showed a bacteriostatic effect.

Conclusions

The use of this new organotypic ex vivo model provides the opportunity to test new drugs against M. abscessus, decreasing the use of costly and tedious animal models.

A TLR2-Activating Fraction From Mycobacterium abscessus Rough Variant Demonstrates Vaccine and Diagnostic Potential

Mycobacterium abscessus is a prevalent pathogenic mycobacterium in cystic fibrosis (CF) patients and one of the most highly drug resistant mycobacterial species to antimicrobial agents. It possesses the property to transition from a smooth (S) to a rough (R) morphotype, thereby influencing the host innate immune response. This transition from the S to the R morphotype takes place in patients with an exacerbation of the disease and a persistence of M. abscessus. We have previously shown that the exacerbation of the Toll-like receptor 2 (TLR2)-mediated inflammatory response, following this S to R transition, is essentially due to overproduction of bacilli cell envelope surface compounds, which we were able to extract by mechanical treatment and isolation by solvent partition in a fraction called interphase. Here, we set up a purification procedure guided by bioactivity to isolate a fraction from the R variant of M. abscessus cells which exhibits a high TLR2 stimulating activity, referred to as TLR2-enriched fraction (TLR2eF). As expected, TLR2eF was found to contain several lipoproteins and proteins known to be stimuli for TLR2. Vaccination with TLR2eF showed no protection toward an M. abscessus aerosol challenge, but provided mild protection in ΔF508 mice and their FVB littermates when intravenously challenged by M. abscessus. Interestingly however, antibodies against TLR2eF compounds were detected during disease in CF patients. In conclusion, we show the potential for compounds in TLR2eF as vaccine and diagnostic candidates, in order to enhance diagnosis, prevent and/or treat M. abscessus-related infections.

Assessment of current diagnostic algorithm for detection of mixed infection with Mycobacterium tuberculosis and nontuberculous mycobacteria

BACKGROUND

The increasing pulmonary diseases are reported to be affected by mixed infection of Mycobacterium tuberculosis (MTB) and nontuberculous mycobacteria (NTM). In this study, our objective was to assess the efficiency of mycobacterial culture plus DNA sequencing to detect the mixed infections with MTB and various NTM organisms. We also aimed to investigate how efficiently GeneXpert detected MTB in mixed infections with NTM in in vitro models.

METHODS

A serial of mixed infection samples was generated by combining suspensions of MTB and five NTM bacteria, respectively. The mixed suspensions were further detected with GeneXpert and liquid culture plus DNA sequencing.

RESULTS

Overall, the GeneXpert assay exhibited promising capability to identify the presence of MTB at different proportions ranging from 1% to 99%. For the liquid culture, the subsequent DNA sequencing only detected the presence of NTM bacteria in the mixed samples, which the proportion of NTM ranged from 1% to 99%, including M. intracellulare, M. kansasii, M. abscessus, and M. fortuitum. For M. avium, DNA sequencing was able to identify the mixtures as M. avium infection in suspensions with no less than 10% M. avium bacteria, whereas only MTB was found in the other suspensions with less M. avium bacteria.

CONCLUSIONS

Our data demonstrate that the current diagnostic algorithm cannot yield a precise detection of mixed infections with MTB and NTM bacteria. The GeneXpert assay only identify MTB in the mixed samples, while the subculture plus DNA sequencing prefers to identify the NTM species with the higher growth rate. Further targeted molecular analysis by specific capture of multiple loci of mycobacterial species from specimens is urgently required to solve this diagnostic dilemma.

Non-tuberculous mycobacteria and the rise of Mycobacterium abscessus

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.

The importance of early diagnosis of Mycobacterium abscessus complex in patients with cystic fibrosis

Mycobacterium abscessus complex can cause severe lung infections and has proven to be a serious threat to patients with cystic fibrosis and a challenge for clinicians due to difficulties in timely diagnosis and complex multidrug treatment regimes. Mycobacterial culture is the gold standard for diagnosis, but in most cystic fibrosis centers it is performed less frequently than culture for other pathogens. Consensus today recommends just one annual mycobacterial culture for asymptomatic patients with cystic fibrosis, a strategy likely to lead to diagnostic delays. Postponement of diagnosis might be the deciding factor in whether an early colonization turns into chronic infection. This review highlights the latest developments in knowledge about the pathogenicity and clinical consequences of M. abscessus complex pulmonary disease, addressing the central theme of why pulmonary infection requires early identification and aggressive antibiotic treatment. The window of opportunity, before M. abscessus complex transforms from a mucosal colonizer to a chronic biofilm infection, is where microbial eradication is most likely to be successful, making early diagnosis essential for improved outcomes.

Clinical course and significance of nontuberculous mycobacteria and its subtypes in cystic fibrosis

BACKGROUND

Nontuberculous mycobacteria (NTM) infections in patients with cystic fibrosis (CF) is increasing globally. However, the related epidemiology, comorbidities, and clinical impact of NTM infection remains unclear in the progress of CF lung disease and patient survival.

METHODS

We performed a retrospective, case-control, cohort study (10 years), comparing NTM culture-positive CF patients (N = 28) to matched controls (N = 26). NTM positive patients were divided in to two groups of slow-growing (N = 17) and rapid- growing NTM (N = 8). Three patients were positive for both slow and rapid NTM. For independent group comparisons, a non-parametric Mann-Whitney test (Kruskal-Wallis test for more than two groups) was used to compare the continuous variables, and a Fisher's exact test was used for the categorical variables. Paired comparisons were performed using a Wilcoxon signed-rank test.

RESULTS

The prevalence of NTM isolation was 8%. The age at CF diagnosis was significantly lower in the slow-growing NTM group compared to the rapidly growing NTM group (P = 0.04). The median percent predicted forced expiratory flow of 25% - 75% (FEF25-75) was significantly higher before NTM acquisition in slow-growing (P = 0.013) and rapidly growing NTM group (P = 0.028). The slow-growing NTM group received significantly more penicillin/beta lactamase (P = 0.010) and rifampin (P = 0.042) following isolation. Macrolide use was significantly higher after isolation in both the slow-growing NTM (P = 0.018) and rapidly growing NTM groups (P = 0.042).

CONCLUSIONS

An earlier CF diagnosis was associated with a higher isolation of slow-growing NTM and greater antimicrobial use after infection. NTM acquisition is associated with a worsening of FEF25-75. Thus, both the early diagnosis and treatment of an NTM infection in patients with CF may positively impact lung function.

Evaluation of the intracellular activity of drugs against Mycobacterium abscessus using a THP-1 macrophage model

We evaluated the antimicrobial effectiveness against M. abscessus in a THP-1 cell line model. No intracellular activity was observed when using amikacin or imipenem. A bacteriostatic effect was observed for cefoxitin, clarithromycin and azithromycin. Tigecycline showed the best antibacterial effect by decreasing the intracellular growth up to bactericidal level.

A Simple and Rapid Gene Disruption Strategy in Mycobacterium abscessus: On the Design and Application of Glycopeptidolipid Mutants

Little is known about the disease-causing genetic determinants that are used by Mycobacterium abscessus, increasingly acknowledged as an important emerging pathogen, notably in cystic fibrosis. The presence or absence of surface exposed glycopeptidolipids (GPL) conditions the smooth (S) or rough (R) M. abscessus subsp. abscessus (M. abscessus) variants, respectively, which are characterized by distinct infective programs. However, only a handful of successful gene knock-out and conditional mutants have been reported in M. abscessus, testifying that genetic manipulation of this mycobacterium is difficult. To facilitate gene disruption and generation of conditional mutants in M. abscessus, we have designed a one-step single cross-over system that allows the rapid and simple generation of such mutants. Cloning of as small as 300 bp of the target gene allows for efficient homologous recombination to occur without additional exogenous recombination-promoting factors. The presence of tdTomato on the plasmids allows easily sifting out the large background of mutants spontaneously resistant to antibiotics. Using this strategy in the S genetic background and the target gene mmpL4a, necessary for GPL synthesis and transport, nearly 100% of red fluorescent clones exhibited a rough morphotype and lost GPL on the surface, suggesting that most red fluorescent colonies obtained after transformation incorporated the plasmid through homologous recombination into the chromosome. This system was further exploited to generate another strain with reduced GPL levels to explore how the presence of these cell wall-associated glycolipids influences M. abscessus hydrophobicity as well as virulence in the zebrafish model of infection. This mutant exhibited a more pronounced killing phenotype in zebrafish embryos compared to its S progenitor and this effect correlated with the production of abscesses in the central nervous system. Overall, these results suggest that the near-complete absence of GPL on the bacterial surface is a necessary condition for optimal pathogenesis of this mycobacterium. They also suggest that GPL content affects hydrophobicity of M. abscessus, potentially altering the aerosol transmission, which is of particular importance from an epidemiological and clinical perspective.

Identification of genes required for Mycobacterium abscessus growth in vivo with a prominent role of the ESX-4 locus

Mycobacterium abscessus, a rapidly growing mycobacterium (RGM) and an opportunistic human pathogen, is responsible for a wide spectrum of clinical manifestations ranging from pulmonary to skin and soft tissue infections. This intracellular organism can resist the bactericidal defense mechanisms of amoebae and macrophages, an ability that has not been observed in other RGM. M. abscessus can up-regulate several virulence factors during transient infection of amoebae, thereby becoming more virulent in subsequent respiratory infections in mice. Here, we sought to identify the M. abscessus genes required for replication within amoebae. To this end, we constructed and screened a transposon (Tn) insertion library of an M. abscessus subspecies massiliense clinical isolate for attenuated clones. This approach identified five genes within the ESX-4 locus, which in M. abscessus encodes an ESX-4 type VII secretion system that exceptionally also includes the ESX conserved EccE component. To confirm the screening results and to get further insight into the contribution of ESX-4 to M. abscessus growth and survival in amoebae and macrophages, we generated a deletion mutant of eccB4 that encodes a core structural element of ESX-4. This mutant was less efficient at blocking phagosomal acidification than its parental strain. Importantly, and in contrast to the wild-type strain, it also failed to damage phagosomes and showed reduced signs of phagosome-to-cytosol contact, as demonstrated by a combination of cellular and immunological assays. This study attributes an unexpected and genuine biological role to the underexplored mycobacterial ESX-4 system and its substrates.

The distinct fate of smooth and rough Mycobacterium abscessus variants inside macrophages

Mycobacterium abscessus is a pathogenic, rapidly growing mycobacterium responsible for pulmonary and cutaneous infections in immunocompetent patients and in patients with Mendelian disorders, such as cystic fibrosis (CF). Mycobacterium abscessus is known to transition from a smooth (S) morphotype with cell surface-associated glycopeptidolipids (GPL) to a rough (R) morphotype lacking GPL. Herein, we show that M. abscessus S and R variants are able to grow inside macrophages and are present in morphologically distinct phagosomes. The S forms are found mostly as single bacteria within phagosomes characterized by a tightly apposed phagosomal membrane and the presence of an electron translucent zone (ETZ) surrounding the bacilli. By contrast, infection with the R form leads to phagosomes often containing more than two bacilli, surrounded by a loose phagosomal membrane and lacking the ETZ. In contrast to the R variant, the S variant is capable of restricting intraphagosomal acidification and induces less apoptosis and autophagy. Importantly, the membrane of phagosomes enclosing the S forms showed signs of alteration, such as breaks or partial degradation. Although not frequently encountered, these events suggest that the S form is capable of provoking phagosome-cytosol communication. In conclusion, M. abscessus S exhibits traits inside macrophages that are reminiscent of slow-growing mycobacterial species.

Increased survival and proliferation of the epidemic strain Mycobacterium abscessus subsp. massiliense CRM0019 in alveolar epithelial cells

BACKGROUND

Outbreaks of infections caused by rapidly growing mycobacteria have been reported worldwide generally associated with medical procedures. Mycobacterium abscessus subsp. massiliense CRM0019 was obtained during an epidemic of postsurgical infections and was characterized by increased persistence in vivo. To better understand the successful survival strategies of this microorganism, we evaluated its infectivity and proliferation in macrophages (RAW and BMDM) and alveolar epithelial cells (A549). For that, we assessed the following parameters, for both M. abscessus CRM0019 as well as the reference strain M. abscessus ATCC 19977: internalization, intracellular survival for up 3 days, competence to subvert lysosome fusion and the intracellular survival after cell reinfection.

RESULTS

CRM0019 and ATCC 19977 strains showed the same internalization rate (approximately 30% after 6 h infection), in both A549 and RAW cells. However, colony forming units data showed that CRM0019 survived better in A549 cells than the ATCC 19977 strain. Phagosomal characteristics of CRM0019 showed the bacteria inside tight phagosomes in A549 cells, contrasting to the loosely phagosomal membrane in macrophages. This observation holds for the ATCC 19977 strain in both cell types. The competence to subvert lysosome fusion was assessed by acidification and acquisition of lysosomal protein. For M. abscessus strains the phagosomes were acidified in all cell lines; nevertheless, the acquisition of lysosomal protein was reduced by CRM0019 compared to the ATCC 19977 strain, in A549 cells. Conversely, in macrophages, both M. abscessus strains were located in mature phagosomes, however without bacterial death. Once recovered from macrophages M. abscessus could establish a new intracellular infection. Nevertheless, only CRM0019 showed a higher growth rate in A549, increasing nearly 10-fold after 48 and 72 h.

CONCLUSION

M. abscessus CRM0019 creates a protective and replicative niche in alveolar epithelial cells mainly by avoiding phagosome maturation. Once recovered from infected macrophages, CRM0019 remains infective and displays greater intracellular growth in A549 cells compared to the ATCC 19977 strain. This evasion strategy in alveolar epithelial cells may contribute to the long survival of the CRM0019 strain in the host and thus to the inefficacy of in vivo treatment.

Is bronchoscopy an obsolete tool in cystic fibrosis? The role of bronchoscopy in cystic fibrosis and its clinical use

Cystic fibrosis (CF) is a progressive life threatening multisystem genetic disease which affects the CF transmembrane conductance regulator channel. Respiratory causes remain the most common mortality in CF. With the onset of newborn screening, initiating treatments both for prophylaxis and disease management, optimizing nutritional support, and developing therapies targeting CF transmembrane conductance regulator protein, this has significantly changed the face of managing this devastating disease. Bronchoscopy and related procedures such as bronchoalveolar lavage (BAL), transbronchial biopsies, and protected brush sampling have been looked at in the management of CF as patients with CF continue to live longer with the help of newer therapies, the microbiome in the lung becomes less diverse along with increased occurrences for noninfectious causes of airway diseases. Though bronchoscopy has been used in conjunction with other modalities such as computed tomography and sputum induction providing a better understanding of the progression of the disease, it still remains valuable in the diagnosis and management of CF.

Controlling Extra- and Intramacrophagic Mycobacterium abscessus by Targeting Mycolic Acid Transport

Mycobacterium abscessus is a rapidly growing mycobacterium (RGM) causing serious infections especially among cystic fibrosis patients. Extremely limited therapeutic options against M. abscessus and a rise in infections with this mycobacterium require novel chemotherapies and a better understanding of how the bacterium causes infection. Different from most RGM, M. abscessus can survive inside macrophages and persist for long durations in infected tissues. We recently delineated differences in the infective programs followed by smooth (S) and rough (R) variants of M. abscessus. Unexpectedly, we found that the S variant behaves like pathogenic slow growing mycobacteria, through maintaining a block on the phagosome maturation process and by inducing phagosome-cytosol communications. On the other hand, R variant infection triggers autophagy and apoptosis, reminiscent of the way that macrophages control RGM. However, the R variant has an exquisite capacity to form extracellular cords, allowing these bacteria to rapidly divide and evade phagocytosis. Therefore, new chemotherapeutic interventions against M. abscessus need to efficiently deal with both the reservoir of intracellular bacilli and the extracellular cords. In this context, we recently identified two chemical entities that were very effective against both M. abscessus populations. Although being structurally unrelated these two chemotypes inhibit the activity of the essential mycolic acid transporter, MmpL3. In this Perspective, we aimed to highlight recent insights into how M. abscessus interacts with phagocytic cells and how the inhibition of mycolic acid transport in this pathogenic RGM could be an efficient means to control both intracellular and extracellular populations of the bacterium.

Targeting Mycolic Acid Transport by Indole-2-carboxamides for the Treatment of Mycobacterium abscessus Infections

Mycobacterium abscessus is a fast-growing, multidrug-resistant organism that has emerged as a clinically significant pathogen in cystic fibrosis (CF) patients. The intrinsic resistance of M. abscessus to most commonly available antibiotics seriously restricts chemotherapeutic options. Herein, we report the potent activity of a series of indolecarboxamides against M. abscessus. The lead compounds, 6 and 12, exhibited strong activity in vitro against a wide panel of M. abscessus isolates and in infected macrophages. High resistance levels to the indolecarboxamides appear to be associated with an A309P mutation in the mycolic acid transporter MmpL3. Biochemical analyses demonstrated that while de novo mycolic acid synthesis remained unaffected, the indolecarboxamides strongly inhibited the transport of trehalose monomycolate, resulting in the loss of trehalose dimycolate production and abrogating mycolylation of arabinogalactan. Our data introduce a hereto unexploited chemical structure class active against M. abscessus infections with promising translational development possibilities for the treatment of CF patients.

Rapidly Growing Mycobacteria

Rapidly growing mycobacteria (RGM) compose approximately one-half of the currently validated mycobacterial species and are divided into six major groups, including the Mycobacterium fortuitum group, M. chelonae/M. abscessus complex, M. smegmatis group, M. mucogenicum group, M. mageritense / M. wolinskyi , and the pigmented RGM. This review discusses each group and highlights the major types of infections associated with each group. Additionally, phenotypic and molecular laboratory identification methods, including gene sequencing, mass spectrometry, and the newly emerging whole-genome sequencing, are detailed, along with a discussion of the current antimicrobial susceptibility methods and patterns of the most common pathogenic species.

Mycobacterium abscessus-Induced Granuloma Formation Is Strictly Dependent on TNF Signaling and Neutrophil Trafficking

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.

The incidence of non-tuberculous mycobacterial infections has recently increased and has even surpassed tuberculosis as a public health concern in many developed countries. These infections require long treatment regimens that are often unsuccessful. Among these, Mycobacterium abscessus has emerged as perhaps the most difficult-to-manage pathogen, especially in cystic fibrosis patients. Unfortunately, very little is known regarding the contributions of the pro-inflammatory and innate immune responses during M. abscessus infection. Here, we exploited the transparency of zebrafish embryos to study, at high resolution, the interactions of M. abscessus with macrophages and neutrophils, and found that both cell types are required to control the infection. We also describe the dramatic consequences of impaired TNF/IL8 immunity on the outcome of the infection. Most importantly, by tracking the dynamics of neutrophil mobilization, we demonstrated the crucial role of these cells in the formation and integrity of protective granulomas. Together, our data provide a significant advance in deciphering the immunopathology of M. abscessus infection, which is particularly relevant for understanding the exquisite vulnerability of cystic fibrosis patients to this bacterium.

MAB_3551c encodes the primary triacylglycerol synthase involved in lipid accumulation in Mycobacterium abscessus

Slow growing pathogenic mycobacteria utilize host-derived lipids and accumulate large amounts of triacylglycerol (TAG) in the form of intracytoplasmic lipid inclusions (ILI), serving as a source of carbon and energy during prolonged infection. Mycobacterium abscessus is an emerging and rapidly growing species capable to induce severe and chronic pulmonary infections. However, whether M. abscessus, like Mycobacterium tuberculosis, possesses the machinery to acquire and store host lipids, remains unaddressed. Herein, we aimed at deciphering the contribution of the seven putative M. abscessus TAG synthases (Tgs) in TAG synthesis/accumulation thanks to a combination of genetic and biochemical techniques and a well-defined foamy macrophage (FM) model along with electron microscopy. Targeted gene deletion and functional complementation studies identified the MAB_3551c product, Tgs1, as the major Tgs involved in TAG production. Tgs1 exhibits a preference for long acyl-CoA substrates and site-directed mutagenesis demonstrated that His144 and Gln145 are essential for enzymatic activity. Importantly, in the lipid-rich intracellular context of FM, M. abscessus formed large ILI in a Tgs1-dependent manner. This supports the ability of M. abscessus to assimilate host lipids and the crucial role of Tgs1 in intramycobacterial TAG production, which may represent important mechanisms for long-term storage of a rich energy supply.

Radiologic computed tomography features of Mycobacterium abscessus in cystic fibrosis

INTRODUCTION

Mycobacterium abscessus infection in cystic fibrosis (CF) patients can lead to poor outcomes. Early diagnosis is important, but there are no studies outlining specific imaging features of M. abscessus in CF.

OBJECTIVES

To describe the computed tomography (CT) findings of early M. abscessus infection in our CF population.

METHODS

Thirteen CF patients with sputum cultures positive for M. abscessus from 2006 to 2013 were identified at our institution. Clinical characteristics including culture dates and lung function were reviewed. Positive cultures were classified as "disease" versus "colonization" based on published criteria. Chest CT scans were reviewed at times closest to initial infection, and features including bronchiectasis, mucous plugging, consolidation, ground glass opacities, nodules, and cavitation were evaluated. Brody scores were calculated to evaluate extent of CF lung disease.

RESULTS

All patients had bronchiectasis and mucous plugging, with 10 of 13 (76.9%) in an upper lobe distribution. Consolidation was seen in 12 of 13 (92.3%) patients, 8 (61.5%) patients had nodules, and 5 (38.5%) with cavitation. The average Brody score was 59.5, which was no different than previously described CF cohorts without M. abscessus. There were no significant differences between subjects with disease versus colonization.

CONCLUSION

The most common CT features of early M. abscessus in our CF population include bronchiectasis, mucus plugging, and consolidation, but the findings did not reveal a unique radiologic signature. CT at this initial time point may not distinguish early M. abscessus infection from background lung disease or mycobacterial colonization in CF patients.

An in vitro model of granuloma-like cell aggregates substantiates early host immune responses against Mycobacterium massiliense infection

Mycobacterium massiliense (M. mass), belonging to the M. abscessus complex, is a rapidly growing mycobacterium that is known to cause tuberculous-like lesions in humans. To better understand the interaction between host cells and M. mass, we used a recently developed in vitro model of early granuloma-like cell aggregates composed of human peripheral blood mononuclear cells (PBMCs). PBMCs formed granuloma-like, small and rounded cell aggregates when infected by live M. mass. Microscopic examination showed monocytes and macrophages surrounded by lymphocytes, which resembled cell aggregation induced by M. tuberculosis (M. tb). M. mass-infected PBMCs exhibited higher expression levels of HLA-DR, CD86 and CD80 on macrophages, and a significant decrease in the populations of CD4+ and CD8+ T cells. Interestingly, low doses of M. mass were sufficient to infect PBMCs, while active host cell death was gradually induced with highly increased bacterial loads, reflecting host destruction and dissemination of virulent rapid-growing mycobacteria (RGM). Collectively, this in vitro model of M. mass infection improves our understanding of the interplay of host immune cells with mycobacteria, and may be useful for developing therapeutics to control bacterial pathogenesis.

Summary: An in vitro model of granuloma-like cell aggregates infected with Mycobacterium massiliense improves our understanding of the interplay of host immune cells with mycobacteria.

Mycobacterium massiliense Induces Macrophage Extracellular Traps with Facilitating Bacterial Growth

Human neutrophils have been known to release neutrophil extracellular traps (NETs), antimicrobial DNA structures capable of capturing and killing microbes. Recently, a similar phenomenon has been reported in macrophages infected with various pathogens. However, a role for macrophages extracellular traps (METs) in host defense responses against Mycobacterium massiliense (M. mass) has yet to be described. In this study, we show that M. mass, a rapid growing mycobacterium (RGM), also induces the release of METs from PMA-differentiated THP-1 cells. Intriguingly, this process is not dependent on NADPH oxidase activity, which regulates NET formation. Instead, M. mass-induced MET formation partially depends on calcium influx and requires phagocytosis of high bacterial load. The METs consist of a DNA backbone embedded with microbicidal proteins such as histone, MPO and elastase. Released METs entrap M. mass and prevent their dissemination, but do not have bactericidal activity. Instead, they result in enhanced bacterial growth. In this regard, METs were considered to provide interaction of M. mass with cells and an environment for bacterial aggregation, which may facilitate mycobacterial survival and growth. In conclusion, our results demonstrate METs as an innate defense response against M. mass infection, and suggest that extracellular traps play a multifaceted role in the interplay between host and bacteria.

Mycobacterium massiliense Type II genotype leads to higher level of colony forming units and TNF-α secretion from human monocytes than Type I genotype

Recently, we introduced a novel Mycobacterium massiliense Type II genotype from Korean patients, in which all isolates showed only a rough (R) colony morphotype. In this study, we sought to compare clinical factors and virulence potentials of two genotypes of M. massiliense, Type I and Type II. Patients infected with Type II tend to be younger at infection than those infected with Type I (56.7 vs 62.3, p = 0.051). Type II was more significantly related to R colony type than Type I (34.1% vs 94.1%, p < 0.001). The Type II strain showed significantly more colony forming units (CFUs) and higher levels of TNF-α secretion in infection of human monocytes than the Type I strain. The challenge of extracted glycopeptidolipid (GPL) into human monocytes indicated that the loss of GPL from the cell wall of the Type II genotype led to a higher level of TNF-α secretion in a toll-like receptor 2(TLR2)-dependent manner. Taken together, our data suggest that the M. massiliense Type II genotype shows higher virulence than Type I, which may be due to the induction of TNF-α via the loss of GPL from the Type II cell wall.

Caspase-independent apoptosis in infected macrophages triggered by sulforaphane via Nrf2/p38 signaling pathways

Mycobacterium abscessus (Mabs), a non-tuberculous mycobacterium, is an emerging and rapidly growing opportunistic pathogen that is frequently found in patients with cystic fibrosis and in immunosuppressed patients. Its high tolerance to antibiotics is of great concern for public health. In this study, our results showed that human THP-1-derived macrophages infected with M. abscessus presented an increase in ROS production and cell necrosis. In addition, M. abscessus infection triggered activation of the Nuclear factor E2-related factor 2 (Nrf2) signaling pathway, and the induction of HO-1 and NQO1 expression levels. Interestingly, pretreatment of macrophages with sulforaphane (SFN), an activator of the antioxidant key regulator Nrf2, followed by M. abscessus infection significantly decreased mycobacterial burden. We demonstrated that this reduction in mycobacterial growth was due to an activation in cell apoptosis in SFN-pretreated and M. abscessus-infected macrophages. Pretreatment with specific MAPK inhibitors, PD98059, SP600125, and SB203580 to ERK, JNK, and p38 respectively, failed to inhibit induction of Nrf2 expression, suggesting that Nrf2 signaling pathway was upstream of MAPK signaling. Activation of cell apoptosis was caspase 3/7 independent but p38 MAPK dependent. Moreover, p38 MAPK induction was abolished in macrophages transfected with Nrf2 siRNA. In addition, p38 inhibitor abolished Nrf2-dependent apoptosis in infected macrophages. Taken together, our results indicate that modulation of the Nrf2 signaling using Nrf2 activators may help potentiate the actual drug therapies used to treat mycobacterial infection.

Pseudo-outbreak ofMycobacterium abscessusInfection Caused by Laboratory Contamination

Objective.

To investigate the cause(s) of an increased incidence of clinical cultures growingMycobacterium abscessusat a hospital in Florida.

Design.

Outbreak investigation.

Setting.

University-affiliated, tertiary-care hospital.

Methods.

A site visit was done during the first week of September 2006. We reviewed the medical records of patients from whomM. abscessuswas recovered during the period from January 1, 2003, through June 30, 2006. We collected environmental samples from various sites and evaluated specimen processing procedures in the microbiology laboratory. Isolates ofM. abscessusrecovered from the environment and from 12 randomly selected patients who sought medical care in 2006 were compared by pulsed-field gel electrophoresis (PFGE). Follow-up case surveillance was continued through March 31, 2007.

Results.

Specimens from 143 patients obtained from various anatomical sites grewM. abscessuson culture in 2005-2006, compared with specimens from 21 patients in 2003-2004. The 12 isolates from patients that were selected for molecular typing had indistinguishable PFGE patterns. Observations revealed no major breaches in the processing of mycobacterial specimens in the laboratory. Isolates grew only after prolonged incubation (mean ± SD, 45 ± 15 days) in test tubes containing diagonally oriented Middlebrook and Cohn 7H10 agar or Lowenstein-Jensen medium. Environmental samples obtained from the inside of the specimen incubator grewM. abscessuson culture. A test tube containing diagonally oriented, uninoculated Middlebrook and Cohn 7H10 agar that was incubated in the same incubator as clinical specimens grewM. abscessuswith a PFGE pattern that matched the pattern of the patient isolates. Cases ofM. abscessusinfection decreased to baseline after the hospital changed suppliers of mycobacterial media and cleaned the incubator.

Conclusions.

Although the source was never confirmed, our investigation suggests that this was a pseudo-outbreak ofM. abscessusinfection that resulted from contamination of mycobacterial cultures during incubation. Our findings emphasize the need for guidance on the disinfection of specimen incubators.

Clinical significance of a first positive nontuberculous mycobacteria culture in cystic fibrosis

RATIONALE

Little is known about outcomes of infection with nontuberculous mycobacteria (NTM) in cystic fibrosis (CF) or about the significance of a positive NTM culture. Determining which patients are at risk for active NTM disease is clinically valuable.

OBJECTIVES

To examine the clinical course of subjects with CF with an initial positive NTM culture and identify characteristics associated with active NTM disease.

METHODS

We performed a retrospective study of pediatric and adult subjects with CF with at least one positive NTM culture at the Colorado CF Center from 2000 to 2010.

MEASUREMENTS AND MAIN RESULTS

Mycobacterium avium complex was the first identified NTM in the majority of subjects (73%). The frequency of growing a second NTM species was 26% at 5 years. Clinical characteristics and distribution of NTM species between pediatric and adult subjects were similar except for differences in baseline FEV1 (89% vs. 71%; P < 0.001) and coinfection with Pseudomonas aeruginosa (33% vs. 55%; P = 0.04). Over 60% of subjects had transient or persistent infection but not active NTM disease. Subjects who developed active NTM disease were distinguished from those with transient or persistent infection, respectively, by FEV1 at the time of first positive NTM culture (72% vs. 84 or 86%; P = 0.02) and FEV1 decline in the prior year (-5.8%/yr vs. -0.7%/yr [P = 0.009] or -0.4%/yr [P = 0.001]).

CONCLUSIONS

The majority of patients with CF with a first positive NTM culture do not progress to active disease. Lower lung function and accelerated lung function decline appear to be indicators of the significance of an initial positive NTM culture.

In vivo assessment of drug efficacy against Mycobacterium abscessus using the embryonic zebrafish test system

Mycobacterium abscessus is responsible for a wide spectrum of clinical syndromes and is one of the most intrinsically drug-resistant mycobacterial species. Recent evaluation of the in vivo therapeutic efficacy of the few potentially active antibiotics against M. abscessus was essentially performed using immunocompromised mice. Herein, we assessed the feasibility and sensitivity of fluorescence imaging for monitoring the in vivo activity of drugs against acute M. abscessus infection using zebrafish embryos. A protocol was developed where clarithromycin and imipenem were directly added to water containing fluorescent M. abscessus-infected embryos in a 96-well plate format. The status of the infection with increasing drug concentrations was visualized on a spatiotemporal level. Drug efficacy was assessed quantitatively by measuring the index of protection, the bacterial burden (CFU), and the number of abscesses through fluorescence measurements. Both drugs were active in infected embryos and were capable of significantly increasing embryo survival in a dose-dependent manner. Protection from bacterial killing correlated with restricted mycobacterial growth in the drug-treated larvae and with reduced pathophysiological symptoms, such as the number of abscesses within the brain. In conclusion, we present here a new and efficient method for testing and compare the in vivo activity of two clinically relevant drugs based on a fluorescent reporter strain in zebrafish embryos. This approach could be used for rapid determination of the in vivo drug susceptibility profile of clinical isolates and to assess the preclinical efficacy of new compounds against M. abscessus.

Shifting paradigms of nontuberculous mycobacteria in cystic fibrosis

Important paradigms of pulmonary disease with nontuberculous mycobacteria (NTM) are currently shifting based on an increasing attention within the field of cystic fibrosis (CF). These shifts are likely to benefit the management of all patients with pulmonary NTM, regardless of underlying pathology. Currently several key areas are being revised: The first outbreak of human NTM transmission has been proven and new evidence of biofilm growth in vivo has been demonstrated. A better understanding of the clinical impact of NTM infection has led to increased diagnostic vigilance and new recommendations for lung transplantation are under way. While recent changes have reinvigorated the interest in NTM disease, the challenge remains, whether such advances can be successfully translated into improved management and care.

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.

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.

Molecular longitudinal tracking of Mycobacterium abscessus spp. during chronic infection of the human lung

The Mycobacterium abscessus complex is an emerging cause of chronic pulmonary infection in patients with underlying lung disease. The M. abscessus complex is regarded as an environmental pathogen but its molecular adaptation to the human lung during long-term infection is poorly understood. Here we carried out a longitudinal molecular epidemiological analysis of 178 M. abscessus spp. isolates obtained from 10 cystic fibrosis (CF) and 2 non CF patients over a 13 year period. Multi-locus sequence and molecular typing analysis revealed that 11 of 12 patients were persistently colonized with the same genotype during the course of the infection while replacement of a M. abscessus sensu stricto strain with a Mycobacterium massiliense strain was observed for a single patient. Of note, several patients including a pair of siblings were colonized with closely-related strains consistent with intra-familial transmission or a common infection reservoir. In general, a switch from smooth to rough colony morphology was observed during the course of long-term infection, which in some cases correlated with an increasing severity of clinical symptoms. To examine evolution during long-term infection of the CF lung we compared the genome sequences of 6 sequential isolates of Mycobacterium bolletii obtained from a single patient over an 11 year period, revealing a heterogeneous clonal infecting population with mutations in regulators controlling the expression of virulence factors and complex lipids. Taken together, these data provide new insights into the epidemiology of M. abscessus spp. during long-term infection of the CF lung, and the molecular transition from saprophytic organism to human pathogen.

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.

Mycobacterium abscessus induces a limited pattern of neutrophil activation that promotes pathogen survival

Mycobacterium abscessus is a rapidly growing mycobacterium increasingly detected in the neutrophil-rich environment of inflamed tissues, including the cystic fibrosis airway. Studies of the immune reaction to M. abscessus have focused primarily on macrophages and epithelial cells, but little is known regarding the neutrophil response despite the predominantly neutrophillic inflammation typical of these infections. In the current study, human neutrophils released less superoxide anion in response to M. abscessus than to Staphylococcus aureus, a pathogen that shares common sites of infection. Exposure to M. abscessus induced neutrophil-specific chemokine and proinflammatory cytokine genes. Although secretion of these protein products was confirmed, the quantity of cytokines released, and both the number and level of gene induction, was reduced compared to S. aureus. Neutrophils mediated killing of M. abscessus, but phagocytosis was reduced when compared to S. aureus, and extracellular DNA was detected in response to both bacteria, consistent with extracellular trap formation. In addition, M. abscessus did not alter cell death compared to unstimulated cells, while S. aureus enhanced necrosis and inhibited apoptosis. However, neutrophils augment M. abscessus biofilm formation. The response of neutrophils to M. abscessus suggests that the mycobacterium exploits neutrophil-rich settings to promote its survival and that the overall neutrophil response was reduced compared to S. aureus. These studies add to our understanding of M. abscessus virulence and suggest potential targets of therapy.

Current dilemmas in antimicrobial therapy in cystic fibrosis

The majority of cystic fibrosis (CF)-related morbidity and mortality is caused by pulmonary damage due to recurrent and chronic infections. Considerable improvements in the survival of individuals with CF have been achieved in recent decades, some of which may be due to better management of common pathogens such as Staphylococcus aureus and Pseudomonas aeruginosa. While the search continues for the optimal approach for prophylaxis, eradication and maintenance treatment of infections, there are several unanswered questions, posing dilemmas related to various therapeutic choices. Microbes pose additional challenges by adapting to CF lungs and developing treatment resistance. Several new, highly antimicrobial-resistant pathogens have emerged. Their pathogenic role in the progression of CF lung disease is not yet clear and effective treatment approaches have not been defined. There is an urgent need for well-designed comparative clinical trials of new antibiotic strategies.

Cord-forming mycobacteria induce DNA meshwork formation by human peripheral blood mononuclear cells

Mononuclear phagocytes, that is, monocytes and macrophages, are central in the defense against mycobacteria. Mycobacterium abscessus is an opportunistic mycobacterial species able to cause chronic pulmonary infections in patients with cystic fibrosis but also soft tissue infections in immunocompetent individuals. Pathogenic isolates of M. abscessus with rough colony morphology form cord-like aggregates. In this study, we investigated the in vitro response of human peripheral blood mononuclear cells (PBMCs) from healthy blood donors to cord-forming M. abscessus strains from cystic fibrosis patients with clinical lung infection. Microscopic examination revealed that the PBMCs produced a coarse fibrous meshwork containing DNA and histones, which surrounded the mycobacterial cords. Thus, the bacterial cord formations were entrapped by monocytes and lymphocytes aggregated onto the DNA-rich meshwork fibers. Mycobacterium abscessus strains with smooth colony morphology, which do not form cords and are readily phagocytosed, did not induce any meshwork formation in PBMCs. The chromatin meshwork may represent a defense mechanism against nondigestible invaders.

Genomic Analysis of Mycobacterium massiliense strain M115, an isolate from human sputum

We report the draft genome sequence of a clinical isolate, strain M115, identified as Mycobacterium massiliense, a member of the newly created taxon of Mycobacterium abscessus subspecies bolletii comb. nov.

Progressive dyspnoea following the treatment of Mycobacterium abscessus infection in an individual with relapsing granulamatosis with polyangitis (Wegener's), complicated by hearing loss requiring cochlear implantation

Backgound

Granulomatosis with polyangitis (Wegener’s) is a vasculitic disease predominantly affecting the lungs, skin, kidneys, ears, nose and throat. Mycobacterium abscessus is an uncommon rapidly growing mycobacterium causing sporadic lung disease. This is the first report of both GPA and Mycobacterium abscessus pulmonary disease reported in literature.

Case Presentation

We present a case report of a 33 year old Caucasian man with relapsing disease complicated by pulmonary infection with Mycobacterium abscessus. He subsequently required bilateral cochlear implantation for progressive sensori-neural hearing loss. His M. abscessus was treated successfully with a prolonged course of antimicrobial therapy. His Granulomatosis with polyangitis (Wegener’s) relapsed towards the end of antimicrobial therapy and required treatment. Shortly after completing his antimicrobial therapy and relapse, he developed progressive dyspnea due to pulmonary fibrosis.

Conclusion

The potential causes of his progressive dyspnoea are discussed including the potential role of his underlying disease and treatment.

Nontuberculous Mycobacterial Pulmonary Infection in Patients with Cystic Fibrosis

The prevalence of nontuberculous mycobacteria (NTM) recovered from patients with cystic fibrosis (CF) appears to be increasing, probably related to improved surveillance and microbiological procedures and an increase in the life expectancy of patients with CF. The distinction between active lung infection and colonization is often difficult to assess in patients with CF because of the marked overlap in the clinical and radiological presentation of CF lung disease and lung disease caused by NTM infection. The possibility of active NTM lung infection should be considered in those patients with compatible radiographic changes and/or progressive deterioration in lung function who do not improve with specific antibiotic therapy and who have repeatedly positive sputum cultures and smears for NTM. Patients with repeatedly positive results of acid-fast smears are more likely to be infected than colonized. Pseudomonas overgrowth may confuse the results of sputum and bronchoalveolar lavage fluid cultures. Decontamination of respiratory samples from patients with CF with 5% oxalic acid results in improved bacteriological recovery of NTM. Skin tests are of limited value as a screening tool for NTM. Since the course of NTM lung infection is often slow, careful follow-up with repeated sputum cultures, chest radiographs and computed tomography (CT) scans may be needed. Treatment of NTM lung disease in patients with CF presents great difficulties because of abnormal gastrointestinal drug absorption and pharmacokinetics in this patient population. Treatment varies according to the mycobacterial species isolated. Long-term multidrug regimens including rifampin (rifampicin) and ethambutol are usually required. Monitoring serum drug levels is a useful indicator of correct dosage in order to prevent adverse effects due to potential drug interactions and altered pharmacokinetics in patients with CF.

Acquisition of clarithromycin resistance mutations in the 23S rRNA gene of Mycobacterium abscessus in the presence of inducible erm(41)

OBJECTIVES

Antibiotic therapy of pulmonary Mycobacterium abscessus infection is based on a combination treatment including clarithromycin. Recent data demonstrated that M. abscessus may carry a chromosomal, inducible erm gene coding for the ribosomal methylase Erm(41). The purpose of this study was to investigate whether in patients with chronic M. abscessus infection undergoing clarithromycin therapy, M. abscessus acquires clarithromycin resistance mutations in the rrl gene in addition to the presence of an inducible Erm(41) methylase.

METHODS

We determined clarithromycin MICs, erm(41) and rrl sequences for 29 clinical M. abscessus subsp. abscessus isolates of five different patients. The isolates were obtained between 2007 and 2011 covering a longitudinal observation period of 2-4 years for the individual patients.

RESULTS

In three out of five patients with an initial rrl wild-type isolate, follow-up isolates demonstrated acquisition of resistance mutations in the rrl gene in addition to the presence of an inducible Erm methylase.

CONCLUSIONS

Our results show that in M. abscessus, clarithromycin resistance mutations in the 23S rRNA peptidyltransferase region provide an additional selective advantage independent of a functional erm(41) gene.

Phagocytosis and cytokine response to rough and smooth colony variants of Mycobacterium abscessus by human peripheral blood mononuclear cells

Mycobacterium abscessus is a non-tuberculous mycobacteria able to cause opportunistic infections in selected patient groups. During the last decades it has emerged as a cause of chronic pulmonary infection in patients with cystic fibrosis (CF). M. abscessus strains exhibit either smooth or rough colony morphology. Strains exhibiting the rough phenotype more often cause pulmonary infections in CF patients than did the smooth ones. Here, we examined phagocytosis and production of cytokines by human peripheral blood mononuclear cells, in response to M. abscessus strains with smooth and rough colony phenotype. The rough isolates all formed multicellular cords, similar to what is observed in Mycobacterium tuberculosis. Monocytes were generally unable to internalize these rough cord isolates, in contrast with the smooth ones. Furthermore, the rough M. abscessus strains induced a distinct cytokine profile differing from that induced by the smooth ones. Rough isolates induced significantly less IL-10 and tumour necrosis factor compared to smooth strains, but more IL-1β. Both varieties induced equal amounts of IFN-γ, IL-17, IL-23, IL-6, IL-8 and equally little IL-12. The ability to withstand phagocytosis might be a virulence factor contributing to the capacity of rough M. abscessus strains to give persistent pulmonary infections.

Antimicrobial susceptibility testing, drug resistance mechanisms, and therapy of infections with nontuberculous mycobacteria

Within the past 10 years, treatment and diagnostic guidelines for nontuberculous mycobacteria have been recommended by the American Thoracic Society (ATS) and the Infectious Diseases Society of America (IDSA). Moreover, the Clinical and Laboratory Standards Institute (CLSI) has published and recently (in 2011) updated recommendations including suggested antimicrobial and susceptibility breakpoints. The CLSI has also recommended the broth microdilution method as the gold standard for laboratories performing antimicrobial susceptibility testing of nontuberculous mycobacteria. This article reviews the laboratory, diagnostic, and treatment guidelines together with established and probable drug resistance mechanisms of the nontuberculous mycobacteria.