Host immune response to rapidly growing mycobacteria, an emerging cause of chronic lung disease

Exploring the Role of a Putative Secondary Metabolite Biosynthesis Pathway in Mycobacterium abscessus Pathogenesis Using a Xenopus laevis Tadpole Model

Mycobacterium abscessus (Mab) is an emerging human pathogen that has a high rate of incidence in immunocompromised individuals. We have found a putative secondary metabolite pathway within Mab, which may be a key factor in its pathogenesis. This novel pathway is encoded in a gene cluster spanning MAB_0284c to 0305 and is related to Streptomyces pathways, producing the secondary metabolites streptonigrin and nybomycin. We constructed an in-frame deletion of the MAB_0295 (phzC) gene and tested it in our Xenopus laevis animal model. We have previously shown that X. laevis tadpoles, which have functional lungs and T cells, can serve as a reliable comparative model for persistent Mab infection and pathogenesis. Here, we report that tadpoles intraperitoneally infected with the ∆phzC mutant exhibit early decreased bacterial loads and significantly increased survival compared with those infected with WT Mab. ∆phzC mutant Mab also induced lower transcript levels of several pro-inflammatory cytokines (IL-1β, TNF-α, iNOS, IFN-γ) than those of WT Mab in the liver and lungs. In addition, there was impaired macrophage recruitment and decreased macrophage infection in tadpoles infected with the ∆phzC mutant, by tail wound inoculation, compared to those infected with the WT bacteria, as assayed by intravital confocal microscopy. These data underline the relevance and usefulness of X. laevis tadpoles as a novel comparative animal model to identify genetic determinants of Mab immunopathogenesis, suggesting a role for this novel and uncharacterized pathway in Mab pathogenesis and macrophage recruitment.

Nitric oxide-releasing prodrug for the treatment of complex Mycobacterium abscessus infections

Non-tuberculosis mycobacteria (NTM) can cause severe respiratory infection in patients with underlying pulmonary conditions, and these infections are extremely difficult to treat. In this report, we evaluate a nitric oxide (NO)-releasing prodrug [methyl tris diazeniumdiolate (MD3)] against a panel of NTM clinical isolates and as a treatment for acute and chronic NTM infections in vivo. Its efficacy in inhibiting growth or killing mycobacteria was explored in vitro alongside evaluation of the impact to primary human airway epithelial tissue. Airway epithelial tissues remained viable after exposure at concentrations of MD3 needed to kill mycobacteria, with no inherent toxic effect from drug scaffold after NO liberation. Resistance studies conducted via serial passage with representative Mycobacterium abscessus isolates demonstrated no resistance to MD3. When administered directly into the lung via intra-tracheal administration in mice, MD3 demonstrated significant reduction in M. abscessus bacterial load in both acute and chronic models of M. abscessus lung infection. In summary, MD3 is a promising treatment for complex NTM pulmonary infection, specifically those caused by M. abscessus, and warrants further exploration as a therapeutic.

Massive and Lengthy Clonal Nosocomial Expansion of Mycobacterium abscessus subsp. massiliense among Patients Who Are Ventilator Dependent without Cystic Fibrosis

Nontuberculous mycobacterial infections are generally believed to be independently acquired from the environment. Although person-to-person transmission of nontuberculous mycobacteria, especially Mycobacterium abscessus subsp. massiliense, is a serious concern among individuals with cystic fibrosis (CF), evidence of its spread among patients without CF has never been established. We unexpectedly found a number of M. abscessus subsp. massiliense cases among patients without CF in a hospital. This study aimed to define the mechanism of M. abscessus subsp. massiliense infection among patients who were ventilator dependent and without CF who had progressive neurodegenerative diseases in our long-term care wards from 2014 to 2018 during suspected nosocomial outbreaks. We conducted whole-genome sequencing of M. abscessus subsp. massiliense isolates from 52 patients and environmental samples. Potential opportunities for in-hospital transmission were analyzed using epidemiological data. M. abscessus subsp. massiliense was isolated from one air sample obtained near a patient without CF who was colonized with M. abscessus subsp. massiliense but not from other potential sources. Phylogenetic analysis of the strains from these patients and the environmental isolate revealed clonal expansion of near-identical M. abscessus subsp. massiliense isolates, with the isolates generally differing by fewer than 22 single nucleotide polymorphisms (SNPs). Approximately half of the isolates differed by fewer than nine SNPs, indicating interpatient transmission. Whole-genome sequencing revealed a potential nosocomial outbreak among patients who were ventilator dependent and without CF. IMPORTANCE The isolation of M. abscessus subsp. massiliense from the air, but not from environmental fluid samples, may suggest airborne transmission. This was the first report to demonstrate person-to-person transmission of M. abscessus subsp. massiliense, even among patients without CF. M. abscessus subsp. massiliense may spread among patients who are ventilator dependent without CF through direct or indirect in-hospital transmission. The current infection control measures should address potential transmission among patients without CF, particularly in facilities that treat patients who are ventilator dependent and patients with preexisting chronic pulmonary diseases, such as CF.

M ycobacterium avium complex genomics and transmission in a London hospital

BACKGROUND

Non-tuberculous mycobacteria (NTM) are environmental microorganisms and opportunistic pathogens in individuals with pre-existing lung conditions such as cystic fibrosis (CF) and non-CF bronchiectasis. While recent studies of Mycobacterium abscessus have identified transmission within single CF centres as well as nationally and globally, transmission of other NTM species is less well studied.

METHODS

To investigate the potential for transmission of the Mycobacterium avium complex (MAC) we sequenced 996 isolates from 354 CF and non-CF patients at the Royal Brompton Hospital (London, UK; collected 2013-2016) and analysed them in a global context. Epidemiological links were identified from patient records. Previously published genomes were used to characterise global population structures.

RESULTS

We identified putative transmission clusters in three MAC species, although few epidemiological links could be identified. For M. avium, lineages were largely limited to single countries, while for Mycobacterium chimaera, global transmission clusters previously associated with heater-cooler units (HCUs) were found. However, the immediate ancestor of the lineage causing the major HCU-associated outbreak was a lineage already circulating in patients.

CONCLUSIONS

CF and non-CF patients shared transmission chains, although the lack of epidemiological links suggested that most transmission is indirect and may involve environmental intermediates or asymptomatic carriage in the wider population.

Preclinical murine models to study lung infection with Mycobacterium abscessus complex

Mycobacterium abscessus is a non-tuberculous mycobacterium (NTM) able to cause invasive pulmonary infections, named NTM pulmonary disease. The therapeutic approaches are limited, and infections are difficult to treat due to antibiotic resistance conferred by an impermeable cell wall, drug efflux pumps, or drug-modifying enzymes. The development of new therapeutics, intended as antimicrobials or drug limiting immunopathology, is urgently necessary. In this context, the preclinical murine models of M. abscessus represent a useful tool to validate and translate in vitro-proofed concepts. These in vivo models are essential for developing new targets and drugs, ameliorating our knowledge in combinatorial regimens of current existing antibiotic treatments, and repurposing existing drugs for new therapeutic options against M. abscessus infection. Thus, this review aims at providing an overview of the current state of the art of preclinical murine models to study M. abscessus lung infection and its exploitation for new therapeutic approaches. This review discusses the murine models available focusing on the different bacterial challenges (aerosol, intranasal, intratracheal, and intravenous administrations), murine genetic background, and additional bacterial related factors. Then, we discuss the successful preclinical models for M. abscessus respiratory infection exploited to study the efficacy and safety of new antimicrobials or to determine the best dosage and route of administration of existing drugs. Finally, we present the current murine models exploited to develop new therapeutic approaches to modulate the host immune response and limit immunopathological damage during M. abscessus lung disease. In conclusion, our review article provides an overview of current and available murine models to characterize acute or chronic infections and to study the outcome of new therapeutic strategies against M. abscessus lung infection.

Rough and smooth variants of Mycobacterium abscessus are differentially controlled by host immunity during chronic infection of adult zebrafish

Prevalence of Mycobacterium abscessus infections is increasing in patients with respiratory comorbidities. After initial colonisation, M. abscessus smooth colony (S) variants can undergo an irreversible genetic switch into highly inflammatory, rough colony (R) variants, often associated with a decline in pulmonary function. Here, we use an adult zebrafish model of chronic infection with R and S variants to study M. abscessus pathogenesis in the context of fully functioning host immunity. We show that infection with an R variant causes an inflammatory immune response that drives necrotic granuloma formation through host TNF signalling, mediated by the tnfa, tnfr1 and tnfr2 gene products. T cell-dependent immunity is stronger against the R variant early in infection, and regulatory T cells associate with R variant granulomas and limit bacterial growth. In comparison, an S variant proliferates to high burdens but appears to be controlled by TNF-dependent innate immunity early during infection, resulting in delayed granuloma formation. Thus, our work demonstrates the applicability of adult zebrafish to model persistent M. abscessus infection, and illustrates differences in the immunopathogenesis induced by R and S variants during granulomatous infection.

The pathogen Mycobacterium abscessus can switch from a smooth colony form (S) into a highly inflammatory, rough colony form (R) during infection. Here, Kam et al. use an adult zebrafish model of M. abscessus chronic infection to illustrate differences in the immunopathogenesis induced by R and S variants.

Increased Virulence of Outer Membrane Porin Mutants of Mycobacterium abscessus

Chronic pulmonary infections caused by non-tuberculous mycobacteria of the Mycobacterium abscessus complex (MABSC) are emerging as a global health problem and pose a threat to susceptible individuals with structural lung disease such as cystic fibrosis. The molecular mechanisms underlying the pathogenicity and intrinsic resistance of MABSC to antibiotics remain largely unknown. The involvement of Msp-type porins in the virulence and biocide resistance of some rapidly growing non-tuberculous mycobacteria and the finding of deletions and rearrangements in the porin genes of serially collected MABSC isolates from cystic fibrosis patients prompted us to investigate the contribution of these major surface proteins to MABSC infection. Inactivation by allelic replacement of the each of the two Msp-type porin genes of M. abscessus subsp. massiliense CIP108297, mmpA and mmpB, led to a marked increase in the virulence and pathogenicity of both mutants in murine macrophages and infected mice. Neither of the mutants were found to be significantly more resistant to antibiotics. These results suggest that adaptation to the host environment rather than antibiotic pressure is the key driver of the emergence of porin mutants during infection.

Subunit vaccine protects against a clinical isolate of Mycobacterium avium in wild type and immunocompromised mouse models

The nontuberculous mycobacteria (NTM) Mycobacterium avium is a clinically significant pathogen that can cause a wide range of maladies, including tuberculosis-like pulmonary disease. An immunocompromised host status, either genetically or acutely acquired, presents a large risk for progressive NTM infections. Due to this quietly emerging health threat, we evaluated the ability of a recombinant fusion protein ID91 combined with GLA-SE [glucopyranosyl lipid adjuvant, a toll like receptor 4 agonist formulated in an oil-in-water stable nano-emulsion] to confer protection in both C57BL/6 (wild type) and Beige (immunocompromised) mouse models. We optimized an aerosol challenge model using a clinical NTM isolate: M. avium 2-151 smt, observed bacterial growth kinetics, colony morphology, drug sensitivity and histopathology, characterized the influx of pulmonary immune cells, and confirmed the immunogenicity of ID91 in both mouse models. To determine prophylactic vaccine efficacy against this M. avium isolate, mice were immunized with either ID91 + GLA-SE or bacillus Calmette-Guérin (BCG). Immunocompromised Beige mice displayed a delayed influx of innate and adaptive immune cells resulting in a sustained and increased bacterial burden in the lungs and spleen compared to C57BL/6 mice. Importantly, both ID91 + GLA-SE and BCG vaccines significantly reduced pulmonary bacterial burden in both mouse strains. This work is a proof-of-concept study of subunit vaccine-induced protection against NTM.

The double-edged sword of Tregs in M tuberculosis, M avium, and M absessus infection

Immunity against different Mycobacteria species targeting the lung requires distinctly different pulmonary immune responses for bacterial clearance. Many parameters of acquired and regulatory immune responses differ quantitatively and qualitatively from immunity during infection with Mycobacteria species. Nontuberculosis Mycobacteria species (NTM) Mycobacterium avium- (M avium), Mycobacterium abscessus-(M abscessus), and the Mycobacteria species Mycobacterium tuberculosis-(Mtb). Herein, we discuss the potential implications of acquired and regulatory immune responses in the context of animal and human studies, as well as future directions for efforts to treat Mycobacteria diseases.

Developing Tadpole Xenopus laevis as a Comparative Animal Model to Study Mycobacterium abscessus Pathogenicity

Mycobacterium abscessus (Mab) is an emerging, nontuberculosis mycobacterium (NTM) that infects humans. Mab has two morphotypes, smooth (S) and rough (R), related to the production of glycopeptidolipid (GPL), that differ in pathogenesis. To further understand the pathogenicity of these morphotypes in vivo, the amphibian Xenopus laevis was used as an alternative animal model. Mab infections have been previously modeled in zebrafish embryos and mice, but Mab are cleared early from immunocompetent mice, preventing the study of chronic infection, and the zebrafish model cannot be used to model a pulmonary infection and T cell involvement. Here, we show that X. laevis tadpoles, which have lungs and T cells, can be used as a complementary model for persistent Mab infection and pathogenesis. Intraperitoneal (IP) inoculation of S and R Mab morphotypes disseminated to tadpole tissues including liver and lungs, persisting for up to 40 days without significant mortality. Furthermore, the R morphotype was more persistent, maintaining a higher bacterial load at 40 days postinoculation. In contrast, the intracardiac (IC) inoculation with S Mab induced significantly greater mortality than inoculation with the R Mab form. These data suggest that X. laevis tadpoles can serve as a useful comparative experimental organism to investigate pathogenesis and host resistance to M. abscessus.

Non-Tuberculous Mycobacteria Interference with BCG-Current Controversies and Future Directions

The global tuberculosis (TB) epidemic caused by the bacterial pathogen Mycobacterium tuberculosis (M.tb) continues unabated. The Mycobacterium bovis bacillus Calmette–Guérin (BCG) vaccination is widely utilized worldwide to protect against infection with M.tb. BCG vaccine protection against TB has had widely varying results for reasons that are not well understood. BCG vaccine interference by non-tuberculosis (NTM) mycobacterial species has been implicated as the potential cause of reduced BCG vaccine efficacy against M.tb. Ongoing efforts to develop new vaccines for TB requires a thorough understanding of the effect of NTM exposure on BCG vaccine efficacy, which may ultimately be a critical determinant of success. We reviewed the conflicting reports on whether NTM interferes with the BCG vaccine, potential explanations to help resolve the controversy, and strategies for developing better animal models. Further studies are needed to longitudinally track the effects of NTM exposure on BCG vaccine-induced host-protective anti-TB immunity.

Mycobacterium abscessus Clearance by Neutrophils Is Independent of Autophagy

Mycobacterium abscessus, a rapidly growing nontuberculous mycobacterium, is increasingly prevalent in chronic lung disease, including cystic fibrosis, and infections are characterized by neutrophil-dominated environments. However, mechanisms of immune control are poorly understood. Azithromycin, a macrolide antibiotic with immunomodulatory effects, is used to treat M. abscessus infections. Recently, inhibition of macrophage bactericidal autophagy was described for azithromycin, which could be detrimental to the host. Therefore, we explored the role of autophagy in mycobactericidal neutrophils. Azithromycin did not affect M. abscessus-induced neutrophil reactive oxygen species formation, phagocytosis, or cytokine secretion, and neutrophils treated with azithromycin killed M. abscessus equally as well as untreated neutrophils from either healthy or cystic fibrosis subjects. One clinical isolate was killed more effectively in azithromycin-treated neutrophils, suggesting that pathogen-specific factors may interact with an azithromycin-sensitive pathway. Chloroquine and rapamycin, an inhibitor and an activator of autophagy, respectively, also failed to affect mycobactericidal activity, suggesting that autophagy was not involved. However, wortmannin, an inhibitor of intracellular trafficking, inhibited mycobactericidal activity, but as a result of inhibiting phagocytosis. The effects of these autophagy-modifying agents and azithromycin in neutrophils from healthy subjects were similar between the smooth and rough morphotypes of M. abscessus However, in cystic fibrosis neutrophils, wortmannin inhibited killing of a rough clinical isolate and not a smooth isolate, suggesting that unique host-pathogen interactions exist in cystic fibrosis. These studies increase our understanding of M. abscessus virulence and of neutrophil mycobactericidal mechanisms. Insight into the immune control of M. abscessus may provide novel targets of therapy.

Characteristics of Circulating CD4+ T Cell Subsets in Patients with Mycobacterium avium Complex Pulmonary Disease

Although prevalence of Mycobacterium avium complex pulmonary disease (MAC-PD) is increasing, limited data are available regarding vulnerability to Mycobacterium avium complex (MAC) infections. To understand the pathobiology of interaction between MAC and host-immunity, it is important to understand the characteristics for circulating T cells in terms of the immunological phenotype and functional correlates in MAC-PD. We aimed to characterize immunophenotype, cytokine profile, and immune inhibitory receptors of circulating CD4⁺ T cells in MAC-PD patients. We enrolled 71 MAC-PD and 20 control individuals. Flow cytometric analysis was performed to determine T cell subsets and immune checkpoint markers. Ex vivo cytokine productions in response to MAC were determined using enzyme-linked immunosorbent assay. The frequencies of CD4⁺ T cells and CD4⁺IL-17⁺ T cells decreased, while CD4⁺IL-4⁺ T cells and CD4⁺CD25⁺Foxp3⁺ T cells increased in peripheral blood mononuclear cells (PBMCs) of MAC-PD individuals upon MAC stimulation compared with those cells in healthy donor-PBMCs. Additionally, we found increased PD-1, CTLA-4, and TIM-3-expressing T cells in MAC- PD individuals in response to MAC-stimulation, indicating that suppressed T cell-mediated response is associated with the susceptibility to MAC infection. These results may help to explain impaired T cell-mediated responses and pave the way for better strategies to achieve protective immunity against MAC infection.

Repurposing drugs for treatment of Mycobacterium abscessus: a view to a kill

BACKGROUND

The current treatment regimens recommended for Mycobacterium abscessus subspecies abscessus (Mab) pulmonary disease are not effective. We identified 16 drugs with potential to build new regimens, translating to 560 possible three-drug combination regimens.

OBJECTIVES

To determine MICs and efficacy of drugs from different antibiotic classes for treatment against Mab, in order to winnow down the potential drugs for combination therapy to tractable numbers, for future use in hollow-fibre studies.

METHODS

The MICs of levofloxacin, minocycline, meropenem, imipenem, tedizolid, bedaquiline, azithromycin, clarithromycin, amikacin, vancomycin, delafloxacin, tebipenem/avibactam and omadacycline were determined for 20 Mab isolates. In addition, concentration-response studies with tedizolid, bedaquiline, clarithromycin, amikacin, tebipenem/avibactam, cefdinir, faropenem, omadacycline and daunorubicin were performed and data were fitted to the inhibitory sigmoid Emax model. Efficacy was defined as maximal kill, expressed as cfu/mL kill below day 0 burden.

RESULTS

The lowest MICs among the 13 antibiotics were of bedaquiline, tebipenem/avibactam and omadacycline. The antibiotics that killed Mab below the day 0 burden were the anticancer agent daunorubicin (3.36 log10 cfu/mL), cefdinir (1.85 log10 cfu/mL), faropenem (2.48 log10 cfu/mL) and tebipenem/avibactam (1.71 log10 cfu/mL kill). The EC50 values of these drugs were 11.67, 9.52, 48.2 and 0.33 mg/L, respectively, below peak concentrations of these drugs.

CONCLUSIONS

The low MICs and efficacy at clinically achievable concentrations mean that tebipenem/avibactam, daunorubicin, omadacycline and bedaquiline give a view of components of a three-drug regimen likely to effectively kill Mab. We propose pharmacokinetic/pharmacodynamic studies to identify such a regimen and the doses to be combined.

The Peroxisome Proliferator-Activated Receptor α- Agonist Gemfibrozil Promotes Defense Against Mycobacterium abscessus Infections

Peroxisome proliferator-activated receptor α (PPARα) shows promising potential to enhance host defenses against Mycobacterium tuberculosis infection. Herein we evaluated the protective effect of PPARα against nontuberculous mycobacterial (NTM) infections. Using a rapidly growing NTM species, Mycobacterium abscessus (Mabc), we found that the intracellular bacterial load and histopathological damage were increased in PPARα-null mice in vivo. In addition, PPARα deficiency led to excessive production of proinflammatory cytokines and chemokines after infection of the lung and macrophages. Notably, administration of gemfibrozil (GEM), a PPARα activator, significantly reduced the in vivo Mabc load and inflammatory response in mice. Transcription factor EB was required for the antimicrobial response against Mabc infection. Collectively, these results suggest that manipulation of PPARα activation has promising potential as a therapeutic strategy for NTM disease.

Non-tuberculous mycobacterial pulmonary disease

Nontuberculous mycobacterial pulmonary disease (NTM-PD) is a challenging infection which is becoming increasingly prevalent, particularly in the elderly, for reasons which are unknown. While underlying lung disease is a well-established risk factor for NTM-PD, it may also occur in apparently healthy individuals. No single common genetic or immunological defect has been identified in this group, and it is likely that multiple pathways contribute towards host susceptibility to NTM-PD which further interact with environmental and microbiological factors leading to the development of disease.The diagnosis of NTM-PD relies on the integration of clinical, radiological and microbiological results. The clinical course of NTM-PD is heterogeneous, with some patients remaining stable without the need for treatment and others developing refractory disease associated with considerable mortality and morbidity. Treatment regimens are based on the identity of the isolated species, drug sensitivity testing (for some agents) and the severity of disease. Multiple antibiotics are typically required for prolonged periods of time and treatment is frequently poorly tolerated. Surgery may be beneficial in selected cases. In some circumstances cure may not be attainable and there is a pressing need for better regimens to treat refractory and drug-resistant NTM-PD.This review summarises current knowledge on the epidemiology, aetiology and diagnosis of NTM-PD and discusses the treatment of two of the most clinically significant species, the M. avium and M. abscessus complexes, with a focus on refractory disease and novel therapies.

IP-10 contributes to the inhibition of mycobacterial growth in an ex vivo whole blood assay

Interferon-γ inducible protein 10 (IP-10), is a potent chemoattractant that promotes migration of monocytes and activated T-cells to inflammation foci. IP-10 is elevated in serum of patients with chronic hepatitis C virus (HCV) and tuberculosis (TB) infections, although it remains to be determined the contribution of IP-10 in restricting Mycobacterium tuberculosis (Mtb) replication. Here, we investigated the impact of IP-10 on mycobacteria replication using the ex vivo model of human whole-blood (WB) assay. In particular, we compared the levels of IP-10 upon infection with different Mtb clinical strains and species of non-tuberculous mycobacteria (NTM) and evaluated how IP-10 may contain bacterial replication. Interestingly, we observed that the inhibition of the host enzyme dipeptidyl peptidase IV (DPP-IV), which inactivates IP-10 through cleavage of two amino acids at the chemokine N-terminus, restricted mycobacterial persistence in WB, supporting the critical role of full length IP-10 in mediating an anti-Mtb response. Addition of recombinant IP-10 expressed in eukaryotic cells enhanced the anti-mycobacterial activity in WB, although no differences were observed when IP-10 containing different proportions of cleaved and non-cleaved forms of the chemokine were added. Moreover, recombinant IP-10 did not exert a direct anti-mycobacterial effect. Our results underscore the clinical relevance of IP-10 in mycobacteria pathogenesis and support the potential outcomes that may derive by targeting the IP-10/CXCR3 pathway as host directed therapies for the treatment of Mtb or NTM infections.

Sodium Hyaluronate Nanocomposite Respirable Microparticles to Tackle Antibiotic Resistance with Potential Application in Treatment of Mycobacterial Pulmonary Infections

Tuberculosis resistant cases have been estimated to grow every year. Besides Mycobacterium tuberculosis, other mycobacterial species are responsible for an increasing number of difficult-to-treat infections. To increase efficacy of pulmonary treatment of mycobacterial infections an inhalable antibiotic powder targeting infected alveolar macrophages (AMs) and including an efflux pump inhibitor was developed. Low molecular weight sodium hyaluronate sub-micron particles were efficiently loaded with rifampicin, isoniazid and verapamil, and transformed in highly respirable microparticles (mean volume diameter: 1 μm) by spray drying. These particles were able to regenerate their original size upon contact with aqueous environment with mechanical stirring or sonication. The in vitro drugs release profile from the powder was characterized by a slow release rate, favorable to maintain a high drug level inside AMs. In vitro antimicrobial activity and ex vivo macrophage infection assays employing susceptible and drug resistant strains were carried out. No significant differences were observed when the powder, which did not compromise the AMs viability after a five-day exposure, was compared to the same formulation without verapamil. However, both preparations achieved more than 80% reduction in bacterial viability irrespective of the drug resistance profile. This approach can be considered appropriate to treat mycobacterial respiratory infections, regardless the level of drug resistance.

Mycobacterium avium Infection in a C3HeB/FeJ Mouse Model

Infections caused by Mycobacterium avium complex (MAC) species are increasing worldwide, resulting in a serious public health problem. Patients with MAC lung disease face an arduous journey of a prolonged multidrug regimen that is often poorly tolerated and associated with relatively poor outcome. Identification of new animal models that demonstrate a similar pulmonary pathology as humans infected with MAC has the potential to significantly advance our understanding of nontuberculosis mycobacteria (NTM) pathogenesis as well as provide a tractable model for screening candidate compounds for therapy. One new mouse model is the C3HeB/FeJ which is similar to MAC patients in that these mice can form foci of necrosis in granulomas. In this study, we evaluated the ability of C3HeB/FeJ mice exposure to an aerosol infection of a rough strain of MAC 2285 to produce a progressive infection resulting in small necrotic foci during granuloma formation. C3HeB/FeJ mice were infected with MAC and demonstrated a progressive lung infection resulting in an increase in bacterial burden peaking around day 40, developed micronecrosis in granulomas and was associated with increased influx of CD4⁺ Th1, Th17, and Treg lymphocytes into the lungs. However, during chronic infection around day 50, the bacterial burden plateaued and was associated with the reduced influx of CD4⁺ Th1, Th17 cells, and increased numbers of Treg lymphocytes and necrotic foci during granuloma formation. These results suggest the C3HeB/FeJ MAC infection mouse model will be an important model to evaluate immune pathogenesis and compound efficacy.

The complexities and challenges of preventing and treating nontuberculous mycobacterial diseases

Seemingly innocuous nontuberculous mycobacteria (NTM) species, classified by their slow or rapid growth rates, can cause a wide range of illnesses, from skin ulceration to severe pulmonary and disseminated disease. Despite their worldwide prevalence and significant disease burden, NTM do not garner the same financial or research focus as Mycobacterium tuberculosis. In this review, we outline the most abundant of over 170 NTM species and inadequacies of diagnostics and treatments and weigh the advantages and disadvantages of currently available in vivo animal models of NTM. In order to effectively combat this group of mycobacteria, more research focused on appropriate animal models of infection, screening of chemotherapeutic compounds, and development of anti-NTM vaccines and diagnostics is urgently needed.

Development of a loop-mediated isothermal amplification coupled lateral flow dipstick targeting erm(41) for detection of Mycobacterium abscessus and Mycobacterium massiliense

Mycobacterium abscessus (M. abscessus) and Mycobacterium massiliense (M. massiliense) are major pathogens that cause post-surgical wound infection and chronic pulmonary disease. Although they are closely related subspecies of M. abscessus complex, their infections are associated with different drug-resistance and cure rate. In the present study, a loop-mediated isothermal amplification (LAMP) coupled with lateral flow dipstick (LFD) method was developed to simultaneous detect M. abscessus and M. massiliense, via specific erm(41) gene. The amplification was carried out at 65 °C for only 60 min, and the results could be visualized on a lateral flow strip. Positive results only occurred in M. abscessus and M. massiliense, no cross-reaction with other mycobacterial species was observed. Therefore, the cost-effective MABC (M. abscessus complex)–LAMP–LFD method developed here was able to correct the diagnose of M. abscessus and M. massiliense infection in a short time. Thus, this method could be used to guide clinicians in treatment of M. abscessus group infections.

Hydroalcoholic Extract and Ethyl Acetate Fraction of Bixa orellana Leaves Decrease the Inflammatory Response to Mycobacterium abscessus Subsp. massiliense

The incidence of infections caused by rapidly growing mycobacteria (RGM), especially Mycobacterium abscessus subsp. massiliense (Mabs), is increasing worldwide. Severe infections are associated with abscess formation and strong inflammatory response. This study evaluated the antimicrobial and anti-inflammatory activities of a hydroalcoholic extract (BoHE) and ethyl acetate fraction (BoEA) of Bixa orellana leaves. Antimicrobial activity was evaluated by broth microdilution to determine the minimum inhibitory (MIC) and the minimum bactericidal (MBC) concentrations. Cytotoxicity was evaluated using erythrocytes and RAW 264.7 cells. Nitric oxide (NO) was assayed in stimulated RAW 264.7 cells, and inflammatory cell migration and acute toxicity were evaluated in a Mabs-induced peritonitis mouse model. The compounds present in BoEA were identified by high performance liquid chromatography and mass spectrometry (HPLC-MS). The MIC and MBC values were 2.34 mg/mL and 37.5 mg/mL for BoHE and 0.39 mg/mL and 6.25 mg/mL for BoEA. The extracts did not induce significant toxicity in erythrocytes and RAW 264.7 cells. High levels of NO induced by Mabs were decreased by treatment with both extracts. The anti-inflammatory activity was confirmed in vivo by significant reduction of the cell migration to the peritoneum following BoHE and BoEA pretreatment. Animals treated with BoHE or BoEA did not show signs of acute toxicity in stomach, liver, and kidney. The chemical characterization of BoEA (the most active extract) revealed that kaempferol-3-O-coumaroyl glucose is its major component. The extract of B. orellana may be effective for treating infections caused by Mabs.

Mycobacterium abscessus Infections in Children: A Review of Current Literature

There is limited literature on Mycobacterium abscessus infections in children and limited data about its diagnosis and management. The incidence of infections due to M abscessus appears to be increasing in certain populations and can be a significant cause of morbidity and mortality.Management of these infections is challenging and relies on combination antimicrobial therapy and debridement of diseased tissue, depending on the site and extent of disease. Treatment regimens often are difficult to tolerate, and the antimicrobials used can cause significant adverse effects, particularly given the long duration of therapy needed.This review summarizes the literature and includes information from our own institution's experience on pediatric M abscessus infections including the epidemiology, transmission, clinical manifestations, and the management of these infections. Adult data have been used where there are limited pediatric data. Further studies regarding epidemiology and risk factors, clinical presentation, optimal treatment, and outcomes in children are necessary.

Anomalies in T Cell Function Are Associated With Individuals at Risk of Mycobacterium abscessus Complex Infection

The increasing global incidence and prevalence of non-tuberculous mycobacteria (NTM) infection is of growing concern. New evidence of person-to-person transmission of multidrug-resistant NTM adds to the global concern. The reason why certain individuals are at risk of NTM infections is unknown. Using high definition flow cytometry, we studied the immune profiles of two groups that are at risk of Mycobacterium abscessus complex infection and matched controls. The first group was cystic fibrosis (CF) patients and the second group was elderly individuals. CF individuals with active M. abscessus complex infection or a history of M. abscessus complex infection exhibited a unique surface T cell phenotype with a marked global deficiency in TNFα production during mitogen stimulation. Importantly, immune-based signatures were identified that appeared to predict at baseline the subset of CF individuals who were at risk of M. abscessus complex infection. In contrast, elderly individuals with M. abscessus complex infection exhibited a separate T cell phenotype underlined by the presence of exhaustion markers and dysregulation in type 1 cytokine release during mitogen stimulation. Collectively, these data suggest an association between T cell signatures and individuals at risk of M. abscessus complex infection, however, validation of these immune anomalies as robust biomarkers will require analysis on larger patient cohorts.

TNF-α-mediated ER stress causes elimination of Mycobacterium fortuitum reservoirs by macrophage apoptosis

Mycobacterium fortuitum (MF), a rapidly growing nontuberculosis mycobacterium, is recognized as an important human pathogen. We investigated whether the endoplasmic reticulum (ER) stress response is associated with the apoptosis of MF-infected macrophages. The expression of ER molecular chaperones was significantly induced by MF infection. We found that MF-induced reactive oxygen species (ROS) generation plays a critical role in the induction of ER stress-mediated apoptosis. Excess TNF-α in the ER led to ER stress-mediated apoptosis during MF infection. The intracellular survival of MF was significantly increased by TNF-α knockdown compared with the control. This is the first report of MF-induced TNF-α as a cause of ER stress in macrophages. Furthermore, we found that TLR2-mediated ER stress response contributed to the elimination of intracellular MF in vivo. These results suggest that TNF-α-mediated ER stress during MF infection contributes to the suppression of intracellular survival of MF in macrophages. Our findings provide new insight into the importance of ER stress in mycobacterial infection.-Oh, S.-M., Lim, Y.-J., Choi, J.-A., Lee, J., Cho, S.-N., Go, D., Kim, S.-H., Song, C.-H. TNF-α-mediated ER stress causes elimination of Mycobacterium fortuitum reservoirs by macrophage apoptosis.

Mycobacterium abscessus Smooth and Rough Morphotypes Form Antimicrobial-Tolerant Biofilm Phenotypes but Are Killed by Acetic Acid

Mycobacterium abscessus has emerged as an important pathogen in people with chronic inflammatory lung diseases such as cystic fibrosis, and recent reports suggest that it may be transmissible by fomites. M. abscessus exhibits two major colony morphology variants: a smooth morphotype (Ma^Sm ) and a rough morphotype (Ma^Rg ). Biofilm formation, prolonged intracellular survival, and colony variant diversity can each contribute to the persistence of M. abscessus and other bacterial pathogens in chronic pulmonary diseases. A prevailing paradigm of chronic M. abscessus infection is that Ma^Sm is a noninvasive, biofilm-forming, persistent phenotype and Ma^Rg an invasive phenotype that is unable to form biofilms. We show that Ma^Rg is hyperaggregative and forms biofilm-like aggregates, which, like Ma^Sm biofilm aggregates, are significantly more tolerant than planktonic variants to acidic pHs, hydrogen peroxide (H₂O₂), and treatment with amikacin or azithromycin. We further show that both variants are recalcitrant to antibiotic treatment inside human macrophage-like cells and that Ma^Rg is more refractory than Ma^Sm to azithromycin. Our results indicate that biofilm-like aggregation and protracted intracellular survival may each contribute to the persistence of this problematic pathogen in the face of antimicrobial agents regardless of morphotype. Biofilms of each M. abscessus variant are rapidly killed, however, by acetic acid, which may help to prevent local fomite transmission.

Epidemiology and Predictors of NTM Pulmonary Infection in Taiwan - a Retrospective, Five-Year Multicenter Study

Multicenter, longitudinal studies on nontuberculous mycobacteria (NTM) pulmonary infection (PI) are lacking. This study provides a 5-year epidemiological overview of NTM-PI in Taiwan and investigated its predictors. The clinical relevance of each respiratory NTM isolate in six hospitals between 2008 and 2014 was determined according to current guidelines. Recurrent episodes were judged by serial bacteriological results. New episodes of NTM-PI and pulmonary colonization (PC) occurring since 2010 were analyzed. Logistic regression analysis was performed to identify the predictors of NTM-PI. Between 2010 and 2014, the incidence rate of NTM-PI was 46.0 episodes per 100,000 hospital-based patient-years. Mycobacterium avium intracellulare complex (MAC) was predominant in Northern Taiwan, whereas MAC and M. abscessus were copredominant in Southern Taiwan. Multiple episodes occurred in 9.5% of NTM-PI patients. No female predominance was observed, except for MAC-PI. Previous pulmonary tuberculosis and chronic obstructive pulmonary disease (COPD) were the most common pulmonary comorbidities and independent risk factors for NTM-PI. Other risk factors included M. kansasii, M. abscessus, and southern Taiwan. Geographical variation of NTM-PI exists in Taiwan. Clinicians should keep a high suspicion on NTM-PI in the risk population. In endemic area of tuberculosis and COPD, there may be no female predominance in NTM-PI.

Causative species of nontuberculous mycobacterial lung disease and comparative investigation on clinical features of Mycobacterium abscessus complex disease: A retrospective analysis for two major hospitals in a subtropical region of Japan

Nontuberculous mycobacteria (NTM) lung disease is increasing globally. Although the etiological epidemiology of NTM is different across regions, Mycobacterium avium complex (MAC) is the leading cause of NTM lung disease in most countries, including mainland Japan. Okinawa is located in the southernmost region of Japan and is the only prefecture categorized as a subtropical region in Japan, it is therefore likely the etiological epidemiology of NTM lung disease is different from mainland Japan. From 2009 to 2015, the medical records of patients, with respiratory specimens positive for NTMs, visiting or admitted to two Okinawan hospitals, were retrospectively analyzed. NTM lung disease cases were defined according to the American Thoracic Society criteria and patient epidemiology and clinical information were evaluated. Results indicate four hundred sixteen patients had bacterial cultures positive for NTM. The most common NTM was M. abscessus complex (MABC) (n = 127; 30.5%), followed by M. intracellulare (n = 85; 20.4%). NTM lung disease was diagnosed in 114 patients. Of these cases, MABC was most common (n = 41; 36.0%), followed by M. intracellulare (n = 31; 27.2%). Chronic obstructive pulmonary disease (COPD) and tracheostomy patients were more likely to develop MABC than MAC lung disease. Multivariate analysis showed a probable association between COPD and MABC lung disease. Chest computed tomography (CT) evaluation revealed bronchiectasis, nodules, and consolidation were less frequently observed in MABC patients compared with MAC patients. Our data suggests Okinawa may be one of the few places where MABC is the predominant pathogen causing NTM lung disease and our results add new insight to MABC lung disease, which is not yet well understood.

galK-based suicide vector mediated allelic exchange in Mycobacterium abscessus

Mycobacterium abscessus is a fast-growing environmental organism and an important emerging pathogen. It is highly resistant to many antibiotics and undergoes a smooth to rough colony morphology change that appears to be important for pathogenesis. Smooth environmental strains have a glycopeptidolipid (GPL) on the surface, while certain types of clinical strains are often rough and lack this GPL, due to mutations in biosynthetic genes or the mmpL4b transporter gene. We report here the development and evaluation of an allelic exchange system for unmarked alleles in M. abscessus ATCC19977, using a suicide vector bearing the E. coli galK gene and 2-deoxygalactose counterselection. We describe here two variant galK suicide vectors, and demonstrate their utility in constructing a variety of mutants with deletion alleles of the mmpL4b GPL transporter gene, the mbtH GPL biosynthesis gene, the known β-lactamase gene MAB_2875 and a putative β-lactamase gene, MAB_2833. We also show that a novel allele of the E. coli aacC4 gene, conferring apramycin resistance (aacC41), can be used as a selectable marker in M. abscessus ATCC19977 at single copy.

US Cystic Fibrosis Foundation and European Cystic Fibrosis Society consensus recommendations for the management of non-tuberculous mycobacteria in individuals with cystic fibrosis

Non-tuberculous mycobacteria (NTM) are ubiquitous environmental organisms that can cause chronic pulmonary infection, particularly in individuals with pre-existing inflammatory lung disease such as cystic fibrosis (CF). Pulmonary disease caused by NTM has emerged as a major threat to the health of individuals with CF but remains difficult to diagnose and problematic to treat. In response to this challenge, the US Cystic Fibrosis Foundation (CFF) and the European Cystic Fibrosis Society (ECFS) convened an expert panel of specialists to develop consensus recommendations for the screening, investigation, diagnosis and management of NTM pulmonary disease in individuals with CF. Nineteen experts were invited to participate in the recommendation development process. Population, Intervention, Comparison, Outcome (PICO) methodology and systematic literature reviews were employed to inform draft recommendations. An anonymous voting process was used by the committee to reach consensus. All committee members were asked to rate each statement on a scale of: 0, completely disagree, to 9, completely agree; with 80% or more of scores between 7 and 9 being considered ‘good’ agreement. Additionally, the committee solicited feedback from the CF communities in the USA and Europe and considered the feedback in the development of the final recommendation statements. Three rounds of voting were conducted to achieve 80% consensus for each recommendation statement. Through this process, we have generated a series of pragmatic, evidence-based recommendations for the screening, investigation, diagnosis and treatment of NTM infection in individuals with CF as an initial step in optimising management for this challenging condition.

Mycobacterium fortuitum induces A20 expression that impairs macrophage inflammatory responses

Mycobacterium fortuitum is a rapidly growing mycobacterium that has been regarded as an etiological agent of a variety of human infections. However, little is known about the host inflammatory responses and the molecular mechanisms by which MF-induced inflammation is regulated in macrophages. In this study, we report that MF infection leads to the induction of an anti-inflammatory molecule, A20 (also known as TNFAIP3), which is essential for the regulation of MF-induced inflammatory responses in murine bone marrow-derived macrophages (BMDMs). MF triggered the expression of tumor necrosis factor-α and interleukin-6 in BMDMs through signaling of the Toll-like receptor 2 (TLR2)-myeloid differentiation primary response gene 88. Additionally, MF rapidly induced the expression of A20, which inhibited proinflammatory cytokine expression and nuclear factor (NF)-κB reporter gene activities in BMDMs. Notably, MF-induced activation of NF-κB signaling was required for A20 expression and proinflammatory responses in BMDMs. Furthermore, the rough morphotype of the MF clinical strain induced a higher level of proinflammatory signaling activation, but less A20 induction in BMDMs, compared to the smooth morphotype. Taken together, these results suggest that MF-induced activation of host proinflammatory responses is negatively regulated through TLR2-dependent A20 expression.

Middle-aged to elderly women have a higher asymptomatic infection rate with Mycobacterium avium complex, regardless of body habitus

Mycobacterium avium complex (MAC) pulmonary disease is prevalent in middle-aged to elderly women with a thin body habitus. By comparing the rate of serologically diagnosed asymptomatic MAC infection and body mass index among 1033 healthy subjects, we find that middle-aged to elderly women became infected with MAC, regardless of their body habitus.

Innate signaling mechanisms controlling Mycobacterium chelonae-mediated CCL2 and CCL5 expression in macrophages

Mycobacterium chelonae (Mch) is an atypical rapidly growing mycobacterium (RGM) that belongs to the M. chelonae complex, which can cause a variety of human infections. During this type of mycobacterial infection, macrophage-derived chemokines play an important role in the mediation of intracellular communication and immune surveillance by which they orchestrate cellular immunity. However, the intracellular signaling pathways involved in the macrophage-induced chemokine production during Mch infections remain unknown. Thus, the present study aimed to determine the molecular mechanisms by which Mch activates the gene expressions of chemokine (C-C motif) ligand 2 (CCL2) and CCL5 in murine bone marrow-derived macrophages (BMDMs) and in vivo mouse model. Toll-like receptor 2 (TLR2)-deficient mice showed increased bacterial burden in spleen and lung and decreased protein expression of CCL2 and CCL5 in serum. Additionally, Mch infection triggered the mRNA and protein expression of CCL2 and CCL5 in BMDMs via TLR2 and myeloid differentiation primary response gene 88 (MyD88) signaling and that it rapidly activated nuclear factor (NF)-κB signaling, which is required for the Mch-induced expressions of CCL2 and CCL5 in BMDMs. Moreover, while the innate receptor Dectin-1 was only partly involved in the Mch-induced expression of the CCL2 and CCL5 chemokines in BMDMs, the generation of intracellular reactive oxygen species (ROS) was an important contributor to these processes. Taken together, the present data indicate that the TLR2, MyD88, and NF-κB pathways, Dectin-1 signaling, and intracellular ROS generation contribute to the Mch-mediated expression of chemokine genes in BMDMs.

Molecular Identification of Clinical Isolates of Mycobacterium fortuitum by Random Amplified Polymorphic DNA (RAPD) Polymerase Chain Reaction and ERIC PCR

BACKGROUNDS

Non tuberculous mycobacteria (NTM) are of importance now-a-days due to their increasing virulence outbreaks and emerging antibiotic resistance. Since the most common NTM in Iran is reportedly Mycobacterium fortuitum, the present study was designed with the aim of molecular identification of clinical isolates of M. foruitum to analyse their heterogeneity.

MATERIALS AND METHODS

A total of 81 isolates of NTM isolated from various samples were collected. The clinical isolates were assigned to species M. fortuitum by using conventional and molecular methods. The DNA banding patterns of ERIC- PCR and RAPD- PCR were analysed by using Bionumeric 7.5 software.

RESULTS

Out of 81 tested NTM, 36 strains of M. fortuitum were identified. 33 isolates were selected for molecular typing in this study. Based on RAPD and ERIC analysis, M. fortuitum isolates were divided into 3 and 6 clusters, respectively. Most of the isolates were distributed into types of II RAPD (20 members/ 60.6 %) and V (14 members/ 42.4% with sub cluster I & II) of ERIC. In RAPD analysis, the major fragments were 300 bp, followed by fragment 1000. In ERIC analysis, the major fragments were 280 bp followed by fragment 1200 bp.

CONCLUSION

In conclusion, though the results from this study represented higher discriminatory power of ERIC, however the combination of RAPD and ERIC analysis were able to sufficiently discriminate the genotypic diversity, infection control, and gain useful epidemiological information regarding M. fortuitum isolates.

Susceptibility of Mycobacterium abscessus to antimycobacterial drugs in preclinical models

Over the last 10 years, Mycobacterium abscessus group strains have emerged as important human pathogens, which are associated with significantly higher fatality rates than any other rapidly growing mycobacteria. These opportunistic pathogens are widespread in the environment and can cause a wide range of clinical diseases, including skin, soft tissue, central nervous system, and disseminated infections; by far, the most difficult to treat is the pulmonary form. Infections with M. abscessus are often multidrug-resistant (MDR) and require prolonged treatment with various regimens and, many times, result in high mortality despite maximal therapy. We report here the evaluation of diverse mouse infection models for their ability to produce a progressive high level of infection with M. abscessus. The nude (nu/nu), SCID (severe combined immunodeficiency), gamma interferon knockout (GKO), and granulocyte-macrophage colony-stimulating factor (GMCSF) knockout mice fulfilled the criteria for an optimal model for compound screening. Thus, we set out to assess the antimycobacterial activity of clarithromycin, clofazimine, bedaquiline, and clofazimine-bedaquiline combinations against M. abscessus-infected GKO and SCID murine infection models. Treatment of GKO and SCID mice with a combination of clofazimine and bedaquiline was the most effective in decreasing the M. abscessus organ burden.

Gallium Compounds Exhibit Potential as New Therapeutic Agents against Mycobacterium abscessus

The rapidly growing nontuberculous mycobacterial species Mycobacterium abscessus has recently emerged as an important pathogen in patients with cystic fibrosis (CF). Treatment options are limited because of the organism's innate resistance to standard antituberculous antibiotics, as well as other currently available antibiotics. New antibiotic approaches to the treatment of M. abscessus are urgently needed. The goal of the present study was to assess the growth-inhibitory activity of different Ga compounds against an American Type Culture Collection (ATCC) strain and clinical isolates of M. abscessus obtained from CF and other patients. In our results, using Ga(NO3)3 and all of the other Ga compounds tested inhibited the growth of ATCC 19977 and clinical isolates of M. abscessus. Inhibition was mediated by disrupting iron uptake, as the addition of exogenous iron (Fe) restored basal growth. There were modest differences in inhibition among the isolates for the same Ga chelates, and for most Ga chelates there was only a slight difference in potency from Ga(NO3)3. In contrast, Ga-protoporphyrin completely and significantly inhibited the ATCC strain and clinical isolates of M. abscessus at much lower concentrations than Ga(NO3)3. In in vitro broth culture, Ga-protoporphyrin was more potent than Ga(NO3)3. When M. abscessus growth inside the human macrophage THP-1 cell line was assessed, Ga-protoporphyrin was >20 times more active than Ga(NO3)3. The present work suggests that Ga exhibits potent growth-inhibitory capacity against the ATCC strain, as well as against antibiotic-resistant clinical isolates of M. abscessus, including the highly antibiotic-resistant strain MC2638. Ga-based therapy offers the potential for further development as a novel therapy against M. abscessus.

Essential engagement of Toll-like receptor 2 in initiation of early protective Th1 response against rough variants of Mycobacterium abscessus

Although Mycobacterium abscessus (M. abscessus) is becoming more prevalent in patients without overt immunodeficiency, little is known about the factors that contribute to disease susceptibility. This study was undertaken to investigate how Toll-like receptor 2 (TLR2) functionally contributes to the generation of protective immunity against M. abscessus in a morphotype-specific manner. We found that Tlr2-/- mice were extremely susceptible to an intravenous (i.v.) model of infection by M. abscessus rough variants, displaying uncontrolled infection in the lungs and a significantly lower survival rate than with wild-type (WT) mice. This uncontrolled infection resulted from failures in the following processes: (i) production of the crucial cytokines gamma interferon (IFN-γ), tumor necrosis factor alpha (TNF-α), and interleukin 12p70 (IL-12p70); (ii) early infiltration of neutrophils, monocytes, and dendritic cells (DCs) in the lungs of Tlr2-/- mice; (iii) rapid influx of CD4+ and CD8+ T cells; and (iv) the expansion of memory/effector T cells. Notably, systemic administration of M. abscessus culture filtrate-treated syngeneic DCs from WT mice greatly strengthened immune priming in vivo, resulting in a dramatic reduction in bacterial growth and improved long-term survival in Tlr2-/- mice, with a recovery of protective immunity. Our findings demonstrate that TLR2 is an essential contributor to instructive and effector immunity during M. abscessus infection in a morphotype-specific manner.

Induction of heme oxygenase-1 contributes to survival of Mycobacterium abscessus in human macrophages-like THP-1 cells

Mycobacterium abscessus (M.abs) is a rapidly growing mycobacterial species that infects macrophages, and is an important pathogen in patients with cystic fibrosis. We studied the early stages of M.abs infection of macrophages, with emphasis on the role of heme-oxygenase-1 (HO-1) in this infection. THP-1 cells were activated using TPA into macrophage-like cells and infected with M.abs for different time points. M.abs infection robustly induced HO-1 expression in the THP-1 cells. Production of HO-1 was p38 MAPK-dependent, as p38 inhibitors suppressed HO-1 induction. Pretreatment with HO-1 inhibitors tin-protoporphyrin (SnPP) significantly inhibited M.abs growth inside macrophages. Furthermore, inhibiting HO-1 using HO-1 siRNA or the HO-1 upstream signaling molecule; Nrf2 using Nrf2 siRNA resulted in similar inhibition of M.abs. In contrast, inducing HO-1 did not increase M.abs intracellular growth above control. Products of HO-1 metabolism of heme are bilirubin, biliverdin, carbon monoxide (CO) and iron. The addition of either bilirubin or biliverdin, but not CO, completely restored the SnPP inhibitory effect and partially that with HO-1 siRNA. To understand the mechanisms, we used Syto-62 labeled M.abs to infect macrophages. Interestingly, HO-1 inhibition promoted M.abs-containing phagosome fusion with lysosomes, which should enhance M.abs killing. M.abs infection enhanced THP-1 ROS production as demonstrated by increased DHE, DCF fluorescence, and EPR signal. HO-1 inhibition further increased ROS production in infected macrophages. Our results indicate that HO-1 induction is important for M.abs growth during the early stages of infection, and that the HO-1 products bilirubin and biliverdin, perhaps through modulation of intracellular ROS levels, may be involved.

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HO-1 induction is important for Mycobacterium abscessus growth inside infected macrophages during the early stages of infection.

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Reducing HO-1 products may enhance the ability of the macrophage to control Mycobacterium abscessus infection.

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HO-1 inhibition increases phagosome–lysosome fusion and thus Mycobacterium abscessus killing.

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.

Importance of reciprocal balance of T cell immunity in Mycobacterium abscessus complex lung disease

Background

Little is known about the nature of the host immune response to Mycobacterium abscessus complex (MABC) infection. The aim of the present study was to investigate whether alterations in serum immunomolecule levels after treating MABC lung disease patients with antibiotics can reflect the disease-associated characteristics.

Methods

A total of 22 immunomolecules in 24 MABC lung disease patients before and after antibiotic therapy were quantitatively analyzed using a multiplex bead-based system.

Results

In general, the pre-treatment levels of T helper type 1 (Th1)-related cytokines, i.e., interferon (IFN)-γ and interleukin (IL)-12, and Th2-related cytokines, i.e., IL-4 and IL-13, were significantly decreased in patients compared with control subjects. In contrast, the pre-treatment levels of Th17-related cytokines, i.e., IL-17 and IL-23, were significantly increased in MABC patients. Interestingly, significantly higher levels of IFN-γ-induced protein (IP)-10 and monokine induced by IFN-γprotein (MIG) were detected in patients with failure of sputum conversion at post-treatment compared to patients with successful sputum conversion.

Conclusion

Reduced Th1 and Th2 responses and enhanced Th17 responses in patients may perpetuate MABC lung disease, and the immunomolecules IP-10 and MIG, induced through IFN-γ, may serve as key markers for indicating the treatment outcome.

Host response to nontuberculous mycobacterial infections of current clinical importance

The nontuberculous mycobacteria are a large group of acid-fast bacteria that are very widely distributed in the environment. While Mycobacterium avium was once regarded as innocuous, its high frequency as a cause of disseminated disease in HIV-positive individuals illustrated its potential as a pathogen. Much more recently, there is growing evidence that the incidence of M. avium and related nontuberculous species is increasing in immunocompetent individuals. The same has been observed for M. abscessus infections, which are very difficult to treat; accordingly, this review focuses primarily on these two important pathogens. Like the host response to M. tuberculosis infections, the host response to these infections is of the TH1 type but there are some subtle and as-yet-unexplained differences.

Increasing nontuberculous mycobacteria infection in cystic fibrosis

BACKGROUND

Nontuberculous mycobacteria (NTM) are emerging infections in the CF population.

AIMS

To assess NTM infection prevalence and associated features in our CF clinic population.

METHODS

Patient records, 2002-2011, were reviewed for NTM infection. FEV1, pancreatic function, sputum microbiology, and serum cytokines were compared in patients with and without NTM infection.

RESULTS

Incidence rate of NTM infection increased from 0 in 2002 to 8.7% in 2011 (p<0.001). NTM infection prevalence increased 3-fold from 5% (4/79) in 2003 to 14.5% (16/110) in 2011 (p=0.05). Prevalence of chronic NTM lung disease has decreased somewhat since a peak in 2009, with institution of aggressive triple therapy. Of NTM-infected compared to uninfected patients, 88.2% vs. 60.3% had a known 'severe' CFTR genotype (p=0.04), 88.2% vs. 58.9% were pancreatic insufficient (p=0.02); 70.6% vs. 43.8% had chronic Pseudomonas aeruginosa (p=0.06); 75% vs. 32% had Aspergillus infection (p=0.007) and 23.5% vs 2.7% had allergic bronchopulmonary aspergillosis (p=0.01). Patients infected with Mycobacterium abscessus had increased TGF-β, TNF-α, IL-1β, IL-2, IL-4 and IL-5 levels (p<0.05). There was no difference in cytokine levels for all NTM infected compared to uninfected patients. M. abscessus comprised 46% of all NTM infections. Comparing M. abscessus versus other NTM, duration was 10.5 (1-118) months versus 1 (1-70) month, median (range) (p=0.004); lung disease occurred in 69% versus 17% (p=0.0004), with sputum conversion in 4/11 versus 5/6, respectively (NS).

CONCLUSIONS

NTM incidence and prevalence have increased dramatically in our CF clinic, associated with a severe CF genotype and phenotype. M. abscessus, the most prevalent NTM, caused prolonged infection despite therapy. There has been some decrease in the prevalence of NTM lung disease since 2009.

Acetic Acid, the active component of vinegar, is an effective tuberculocidal disinfectant

Effective and economical mycobactericidal disinfectants are needed to kill both Mycobacterium tuberculosis and non-M. tuberculosis mycobacteria. We found that acetic acid (vinegar) efficiently kills M. tuberculosis after 30 min of exposure to a 6% acetic acid solution. The activity is not due to pH alone, and propionic acid also appears to be bactericidal. M. bolletii and M. massiliense nontuberculous mycobacteria were more resistant, although a 30-min exposure to 10% acetic acid resulted in at least a 6-log10 reduction of viable bacteria. Acetic acid (vinegar) is an effective mycobactericidal disinfectant that should also be active against most other bacteria. These findings are consistent with and extend the results of studies performed in the early and mid-20th century on the disinfectant capacity of organic acids. IMPORTANCE Mycobacteria are best known for causing tuberculosis and leprosy, but infections with nontuberculous mycobacteria are an increasing problem after surgical or cosmetic procedures or in the lungs of cystic fibrosis and immunosuppressed patients. Killing mycobacteria is important because Mycobacterium tuberculosis strains can be multidrug resistant and therefore potentially fatal biohazards, and environmental mycobacteria must be thoroughly eliminated from surgical implements and respiratory equipment. Currently used mycobactericidal disinfectants can be toxic, unstable, and expensive. We fortuitously found that acetic acid kills mycobacteria and then showed that it is an effective mycobactericidal agent, even against the very resistant, clinically important Mycobacterium abscessus complex. Vinegar has been used for thousands of years as a common disinfectant, and if it can kill mycobacteria, the most disinfectant-resistant bacteria, it may prove to be a broadly effective, economical biocide with potential usefulness in health care settings and laboratories, especially in resource-poor countries.

Mycobacterium massiliense induces inflammatory responses in macrophages through Toll-like receptor 2 and c-Jun N-terminal kinase

Mycobacterium massiliense (Mmass) is an emerging, rapidly growing mycobacterium (RGM) that belongs to the M. abscessus (Mabc) group, albeit clearly differentiated from Mabc. Compared with M. tuberculosis, a well-characterized human pathogen, the host innate immune response against Mmass infection is largely unknown. In this study, we show that Mmass robustly activates mRNA and protein expression of tumor necrosis factor (TNF)-α and interleukin (IL)-6 in murine bone marrow-derived macrophages (BMDMs). Toll-like receptor (TLR)-2 and myeloid differentiation primary response gene 88 (MyD88), but neither TLR4 nor Dectin-1, are involved in Mmass-induced TNF-α or IL-6 production in BMDMs. Mmass infection also activates the mitogen-activated protein kinase (MAPKs; c-Jun N-terminal kinase (JNK), ERK1/2 and p38 MAPK) pathway. Mmass-induced TNF-α and IL-6 production was dependent on JNK activation, while they were unaffected by either the ERK1/2 or p38 pathway in BMDMs. Additionally, intracellular reactive oxygen species (ROS), NADPH oxidase-2, and nuclear factor-κB are required for Mmass-induced proinflammatory cytokine generation in macrophages. Furthermore, the S morphotype of Mmass showed lower overall induction of pro-inflammatory (TNF-α, IL-6, and IL-1β) and anti-inflammatory (IL-10) cytokines than the R morphotype, suggesting fewer immunogenic characteristics for this clinical strain. Together, these results suggest that Mmass-induced activation of host proinflammatory cytokines is mediated through TLR2-dependent JNK and ROS signaling pathways.