Overexpression of proinflammatory TLR-2-signalling lipoproteins in hypervirulent mycobacterial variants

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.

Surface-exposed proteins of pathogenic mycobacteria and the role of cu-zn superoxide dismutase in macrophages and neutrophil survival

Pathogenic mycobacteria are important agents causing human disease. Mycobacterium avium subsp. hominissuis (M. avium) is a species of recalcitrant environmental pathogen. The bacterium forms robust biofilms that allow it to colonize and persist in austere environments, such as residential and commercial water systems. M. avium is also an opportunistic pathogen that is a significant source of mortality for immune-compromised individuals. Proteins exposed at the bacterial surface play a central role in mediating the relationship between the bacterium and its environment. The processes underlying both biofilm formation and pathogenesis are directly dependent on this essential subset of the bacterial proteome. Therefore, the characterization of the surface-exposed proteome is an important step towards an improved understanding of the mycobacterial biology and pathogenesis. Here we examined the complement of surface exposed proteins from Mycobacterium avium 104, a clinical isolate and reference strain of Mycobacterium avium subsp. hominissuis. To profile the surface-exposed proteins of viable M. avium 104, bacteria were covalently labeled with a membrane impermeable biotinylation reagent and labeled proteins were affinity purified via the biotin-streptavidin interaction. The results provide a helpful snapshot of the surface-exposed proteome of this frequently utilized reference strain of M. avium. A Cu-Zn SOD knockout mutant, MAV_2043, a surface identified protein, was evaluated regarding its role in the survival in both macrophages and neutrophils.

Increased phagocytosis of Mycobacterium marinum mutants defective in lipooligosaccharide production: a structure-activity relationship study

Mycobacterium marinum is a waterborne pathogen responsible for tuberculosis-like infections in ectotherms and is an occasional opportunistic human pathogen. In the environment, M. marinum also interacts with amoebae, which may serve as a natural reservoir for this microorganism. However, the description of mycobacterial determinants in the early interaction with macrophages or amoebae remains elusive. Lipooligosaccharides (LOSs) are cell surface-exposed glycolipids capable of modulating the host immune system, suggesting that they may be involved in the early interactions of M. marinum with macrophages. Herein, we addressed whether LOS composition affects the uptake of M. marinum by professional phagocytes. Mutants with various truncated LOS variants were generated, leading to the identification of several previously uncharacterized biosynthetic genes (wbbL2, MMAR_2321, and MMAR_2331). Biochemical and structural approaches allowed resolving the structures of LOS precursors accumulating in this set of mutants. These strains with structurally defined LOS profiles were then used to infect both macrophages and Acanthamoebae. An inverse correlation between LOS completeness and uptake of mycobacteria by phagocytes was found, allowing the proposal of three mutant classes: class I (papA4), devoid of LOS and highly efficiently phagocytosed; class II, accumulating only early LOS intermediates (wbbL2 and MMAR_2331) and efficiently phagocytosed but less than class I mutants; class III, lacking LOS-IV (losA, MMAR_2319, and MMAR_2321) and phagocytosed similarly to the control strain. These results indicate that phagocytosis is conditioned by the LOS pattern and that the LOS pathway used by M. marinum in macrophages is conserved during infection of amoebae.

Structure and function of mycobacterium glycopeptidolipids from comparative genomics perspective

Glycopeptidolipids (GPLs) attached to the outer surface of the greasy cell envelope, are a class of important glycolipids synthesized by several non-tuberculosis mycobacteria. The deletion or structure change of GPLs confers several phenotypical changes including colony morphology, hydrophobicity, aggregation, sliding motility, and biofilm formation. In addition, GPLs, particular serovar specific GPLs, are important immunomodulators. This review aims to summarize the advance on the structure, function and biosynthesis of mycobacterium GPLs.

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.

Mycobacterium abscessus bacteremia after receipt of intravenous infusate of cytokine-induced killer cell therapy for body beautification and health boosting

BACKGROUND

We report the first series of Mycobacterium abscessus bacteremia after cytokine-induced killer cell therapy for body beautification and health boosting.

METHODS

The clinical manifestations, laboratory and radiological investigations, cytokine/chemokine profiles, and outcomes were described and analyzed.

RESULTS

Four patients were admitted, and 3 patients had septic shock. Chest radiographs showed pulmonary infiltrates in all patients. Three patients developed peripheral gangrene, and 1 patient required lower limb and finger amputations. Patient 1 also developed disseminated infection including meningitis and urinary tract infection. Postmortem examination of patient 1 showed focal areas of pulmonary hemorrhage and diffuse alveolar damage, splenic infarct, adrenal necrosis, and hemorrhage, and acid-fast bacilli (AFB) were seen in the lung, liver, kidney, and adrenal gland. Patient 2 developed inguinal granulomatous lymphadenitis about 40 days after onset of lower limb gangrene. Wedge-shaped pulmonary infarcts were found in patient 3, and retinitis and subcutaneous lesions developed in patient 4. Patients in septic shock had dysregulated cytokine/chemokine profiles. Patient 4 with relatively milder presentation had increasing levels of interleukin 17 and cytokines in the interferon-γ/interleukin 12 pathway. All survivors required prolonged intravenous antibiotics. Blood cultures grew M. abscessus for all patients, and admission peripheral blood smear revealed AFB for 3 patients. Mycobacterium abscessus was also isolated from respiratory specimens (2 patients), urine (1 patient), and cerebrospinal fluid (1 patient). Time to initial blood culture positivity (patients 1, 2, and 3: ≤52 hours; patient 4: 83 hours) appeared to correlate with disease severity.

CONCLUSIONS

Empirical coverage for rapidly growing mycobacteria should be considered in patients with sepsis following cosmetic procedures.

Clinical significance of respiratory isolates for Mycobacterium abscessus complex from pediatric patients

Mycobacterium abscessus complex is the most virulent of rapidly growing mycobacteria causing invasive lung disease. To better delineate clinical pediatric experience and outcomes with M. abscessus complex, we retrospectively gathered 5-year data on M. abscessus complex infection and outcomes in a large, hospital-based pediatric pulmonary center. Patients were selected from the database of the microbiology department at Miller Children's Hospital in Long Beach, CA. Patients had at least one positive pulmonary isolate for M. abscessus complex from February 2006 to May 2011. Treatment modality data were collected and successful therapy of disease was determined as clearance of M. abscessus complex infection after antibiotics proven by culture negative respiratory isolate within at least 12 months of therapy initiation. Two cystic fibrosis patients with M. abscessus complex were identified, one with failed therapy and the other with stable pulmonary status despite persistent isolation. One primary ciliary dyskinesia patient had successful clearance of M. abscessus complex, however is now growing M. avium intracellulare. A patient with no prior medical history was successfully treated with antimycobacterial therapy. Eleven patients with neuromuscular disorders had tracheal aspirates positive for M. abscessus complex. None were treated due to stable lung status and all but two had spontaneous clearance of the mycobacteria. The two remaining persist with sporadic isolation of M. abscessus complex without clinical significance. We concluded that patients with tracheostomy associated M. abscessus complex infections do not appear to require treatment and often have spontaneous resolution. Cystic fibrosis or primary ciliary dyskinesia patients may have clinical disease warranting treatment, but current antimycobacterial therapy has not proven to be completely successful. As M. abscessus complex gains prevalence, standardized guidelines for diagnosis and therapy are needed in the pediatric population. Multicenter cohort analysis is necessary to achieve such guidelines.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Regulation of oxidative stress by Nrf2 in the pathophysiology of infectious diseases

The innate immune system, including phagocytic cells, is the first line of defense against pathogens. During infection by microorganisms such as viruses, bacteria, or parasites, phagocytic cells produce an excess of oxidants, a crucial process for the clearance of pathogens. This increase in oxidants creates an imbalance between oxidants and endogenous antioxidants. Left unchecked, this acute or chronic oxidative stress can lead to apoptotic cell-death and oxidative stress-induced diseases including neurodegenerative and cardiovascular disorders, premature aging, secondary infections, and cancer. The activation of nuclear factor E2-related factor 2 (Nrf2) is an efficient antioxidant defensive mechanism used by host cells to counteract oxidative stress. The transcription factor Nrf2 has been identified as the master regulator of several hundred of genes involved in the antioxidant defense response. The review objectives were to collect recent findings on the contribution of oxidative stress to complications of infection, and to highlight the beneficial impact of antioxidants in reducing inflammation and oxidant-related tissue damage. Furthermore, a direct relationship between infection and decline in Nrf2 activity has been demonstrated. Thus, an interesting therapeutic approach in disease prevention and treatment of stress-related diseases may consist in optimizing antibiotic or antiviral therapy with a combination of Nrf2 inducer treatment.

Abnormal high-density lipoprotein induces endothelial dysfunction via activation of Toll-like receptor-2

Endothelial injury and dysfunction (ED) represent a link between cardiovascular risk factors promoting hypertension and atherosclerosis, the leading cause of death in Western populations. High-density lipoprotein (HDL) is considered antiatherogenic and known to prevent ED. Using HDL from children and adults with chronic kidney dysfunction (HDL(CKD)), a population with high cardiovascular risk, we have demonstrated that HDL(CKD) in contrast to HDL(Healthy) promoted endothelial superoxide production, substantially reduced nitric oxide (NO) bioavailability, and subsequently increased arterial blood pressure (ABP). We have identified symmetric dimethylarginine (SDMA) in HDL(CKD) that causes transformation from physiological HDL into an abnormal lipoprotein inducing ED. Furthermore, we report that HDL(CKD) reduced endothelial NO availability via toll-like receptor-2 (TLR-2), leading to impaired endothelial repair, increased proinflammatory activation, and ABP. These data demonstrate how SDMA can modify the HDL particle to mimic a damage-associated molecular pattern that activates TLR-2 via a TLR-1- or TLR-6-coreceptor-independent pathway, linking abnormal HDL to innate immunity, ED, and hypertension.

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.

Differential trafficking of TLR1 I602S underlies host protection against pathogenic mycobacteria

We recently identified I602S as a frequent single-nucleotide polymorphism of human TLR1 that greatly inhibits cell surface trafficking, confers hyporesponsiveness to TLR1 agonists, and protects against the mycobacterial diseases leprosy and tuberculosis. Because mycobacteria are known to manipulate the TLR system to their advantage, we hypothesize that the hyporesponsive 602S variant may confer protection by enabling the host to overcome this immune subversion. We report that primary human monocytes and macrophages from homozygous TLR1 602S individuals are resistant to mycobacterial-induced downregulation of macrophage MHC class II, CD64, and IFN-γ responses compared with individuals who harbor the TLR1 602I variant. Additionally, when challenged with mycobacterial agonists, macrophages from TLR1 602S/S individuals resist induction of host arginase-1, an enzyme that depletes cellular arginine stores required for the production of antimicrobial reactive nitrogen intermediates. The differences in cell activation mediated by TLR1 602S and TLR1 602I are observed upon stimulation with soluble mycobacterial-derived agonists but not with whole mycobacterial cells. Taken together, these results suggest that the TLR1 602S variant protects against mycobacterial disease by preventing soluble mycobacterial products, perhaps released from granulomas, from disarming myeloid cells prior to their encounter with whole mycobacteria.

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.

Conditional gene expression in Mycobacterium abscessus

Mycobacterium abscessus is an emerging human pathogen responsible for lung infections, skin and soft-tissue infections and disseminated infections in immunocompromised patients. It may exist either as a smooth (S) or rough (R) morphotype, the latter being associated with increased pathogenicity in various models. Genetic tools for homologous recombination and conditional gene expression are desperately needed to allow the study of M. abscessus virulence. However, descriptions of knock-out (KO) mutants in M. abscessus are rare, with only one KO mutant from an S strain described so far. Moreover, of the three major tools developed for homologous recombination in mycobacteria, only the one based on expression of phage recombinases is working. Several conditional gene expression tools have recently been engineered for Mycobacterium tuberculosis and Mycobacterium smegmatis, but none have been tested yet in M. abscessus. Based on previous experience with genetic tools allowing homologous recombination and their failure in M. abscessus, we evaluated the potential interest of a conditional gene expression approach using a system derived from the two repressors system, TetR/PipOFF. After several steps necessary to adapt TetR/PipOFF for M. abscessus, we have shown the efficiency of this system for conditional expression of an essential mycobacterial gene, fadD32. Inhibition of fadD32 was demonstrated for both the S and R isotypes, with marginally better efficiency for the R isotype. Conditional gene expression using the dedicated TetR/PipOFF system vectors developed here is effective in S and R M. abscessus, and may constitute an interesting approach for future genetic studies in this pathogen.

Characteristics of Mycobacterium smegmatis J15cs strain lipids

Mycobacterium smegmatis is a rapidly growing, non-pathogenic mycobacterium, and M. smegmatis strain mc(2)155 in particular has been used as a tool for molecular analysis of mycobacteria because of its high rate of transformation. We examined another strain, M. smegmatis J15cs, which has the advantage of surviving for six days in murine macrophages. The J15cs strain produces a rough dry colony, and we hypothesized that the long survival of the J15cs strain was correlated with its cell wall components. Therefore, the lipid compositions of these two strains were compared. The subclasses and carbon species of the mycolic acids were very similar, and the major glycolipids and phospholipids were expressed in both strains. However, apolar glycopeptidolipids were deleted only in the J15cs strain. The presence of apolar glycopeptidolipids gives the cell wall a different structure. Moreover, the apolar glycopeptidolipids were recognized by macrophages via toll-like receptor 2, but not 4. We concluded that the absence of apolar glycopeptidolipids is a definitive feature of the J15cs strain, and affects its morphology and survival in host cells.