Genetic Involvement of Mycobacterium avium Complex in the Regulation and Manipulation of Innate Immune Functions of Host Cells

Development of a silkworm infection model for evaluating the virulence of Mycobacterium intracellulare subspecies estimated using phylogenetic tree analysis based on core gene data

Non-tuberculous mycobacteria (NTM) cause skin infections, respiratory diseases, and disseminated infections. Mycobacterium avium and Mycobacterium intracellulare, which are slow grown Mycobacterium, are main agents of those NTM diseases. A silkworm infection model with Mycobacterium abscessus, a rapidly growing Mycobacterium species, was established to quantitatively evaluate its virulence within a short period. However, a silkworm infection model to quantitatively evaluate the virulence of M. intracellulare has not yet been developed. In this study, we determined the virulence of M. intracellulare subspecies within 4 days using a silkworm infection model. The subspecies of M. intracellulare strains used in this study were estimated by phylogenetic tree analysis using core gene data. The median lethal dose (LD50) values, which are the dose of a pathogen required to kill half of the silkworms in a group, were determined 4 days after infection. The LD50 value of M. intracellulare subsp. chimaera DSM44623 was higher than that of M. intracellulare subsp. intracellulare ATCC13950. These results suggest that the virulence of M. intracellulare subspecies can be compared using a silkworm model within 4 days.

Genetic and chemical control of tuberculostearic acid production in Mycobacterium avium subspecies paratuberculosis

Tuberculostearic acid (TBSA) is a fatty acid unique to mycobacteria and some corynebacteria and has been studied due to its diagnostic value, biofuel properties, and role in membrane dynamics. In this study, we demonstrate that TBSA production can be abrogated either by addition of pivalic acid to mycobacterial growth cultures or by a bfaA gene knockout encoding a flavin adenine dinucleotide (FAD)-binding oxidoreductase. Mycobacterium avium subspecies paratuberculosis (Map) growth and TBSA production were inhibited in 0.5-mg/mL pivalic acid-supplemented cultures, but higher concentrations were needed to have a similar effect in other mycobacteria, including Mycobacterium smegmatis. While Map C-type strains, isolated from cattle and other ruminants, will produce TBSA in the absence of pivalic acid, the S-type Map strains, typically isolated from sheep, do not produce TBSA in any condition. A SAM-dependent methyltransferase encoded by bfaB and FAD-binding oxidoreductase are both required in the two-step biosynthesis of TBSA. However, S-type strains contain a single-nucleotide polymorphism in the bfaA gene, rendering the oxidoreductase enzyme vestigial. This results in the production of an intermediate, termed 10-methylene stearate, which is detected only in S-type strains. Fatty acid methyl ester analysis of a C-type Map bfaA knockout revealed the loss of TBSA production, but the intermediate was present, similar to the S-type strains. Collectively, these results demonstrate the subtle biochemical differences between two primary genetic lineages of Map and other mycobacteria as well as explain the resulting phenotype at the genetic level. These data also suggest that TBSA should not be used as a diagnostic marker for Map.IMPORTANCEBranched-chain fatty acids are a predominant cell wall component among species belonging to the Mycobacterium genus. One of these is TBSA, which is a long-chain middle-branched fatty acid used as a diagnostic marker for Mycobacterium tuberculosis. This fatty acid is also an excellent biolubricant. Control of its production is important for industrial purposes as well as understanding the biology of mycobacteria. In this study, we discovered that a carboxylic acid compound termed pivalic acid inhibits TBSA production in mycobacteria. Furthermore, Map strains from two separate genetic lineages (C-type and S-type) showed differential production of TBSA. Cattle-type strains of Mycobacterium avium subspecies paratuberculosis produce TBSA, while the sheep-type strains do not. This important phenotypic difference is attributed to a single-nucleotide deletion in sheep-type strains of Map. This work sheds further light on the mechanism used by mycobacteria to produce tuberculostearic acid.

Anticancer and Antibacterial Properties of Curcumin-Loaded Mannosylated Solid Lipid Nanoparticles for the Treatment of Lung Diseases

Lung cancer and Mycobacterium avium complex infection are lung diseases associated with high incidence and mortality rates. Most conventional anticancer drugs and antibiotics have certain limitations, including high drug resistance rates and adverse effects. Herein, we aimed to synthesize mannose surface-modified solid lipid nanoparticles (SLNs) loaded with curcumin (Man-CUR SLN) for the effective treatment of lung disease. The synthesized Man-CUR SLNs were analyzed using various instrumental techniques for structural and physicochemical characterization. Loading curcumin into SLNs improved the encapsulation efficiency and drug release capacity, as demonstrated by high-performance liquid chromatography analysis. Furthermore, we characterized the anticancer effect of curcumin using the A549 lung cancer cell line. Cells treated with Man-CUR SLN exhibited an increased cellular uptake and cytotoxicity. Moreover, treatment with free CUR could more effectively reduce cancer migration than treatment with Man-CUR SLNs. Similarly, free curcumin elicited a stronger apoptosis-inducing effect than that of Man-CUR SLNs, as demonstrated by reverse transcription-quantitative PCR analysis. Finally, we examined the antibacterial effects of free curcumin and Man-CUR SLNs against Mycobacterium intracellulare (M.i.) and M.i.-infected macrophages, revealing that Man-CUR SLNs exerted the strongest antibacterial effect. Collectively, these findings indicate that mannose-receptor-targeted curcumin delivery using lipid nanoparticles could be effective in treating lung diseases. Accordingly, this drug delivery system can be used to target a variety of cancers and immune cells.

Mycobacterial Interspersed Repeat Unit-Variable Number Tandem Repeat Typing of Mycobacterium avium Strains Isolated from the Lymph Nodes of Free-Living Carnivorous Animals in Poland

Non-tuberculous mycobacteria (NTM) are ubiquitous organisms, of which some, especially those of the Mycobacterium avium complex (MAC), may be opportunistic animal and human pathogens. Infection with NTM can interfere with tuberculosis (TB) diagnosis and induce zoonoses, especially in immunocompromised individuals. Diseases caused by NTM have become more readily recognized; however, they are likely still underestimated. In this study, we identified and genotyped Mycobacterium avium strains that were isolated during TB monitoring among free-living carnivorous animals from southeastern Poland. In 2011-2020, lymph node samples from 192 such animals were tested for mycobacteria. A total of 41 isolates of M. avium strains were detected with the use of IS901, IS900, IS1245, and mycobacterial interspersed repeat unit-variable number tandem repeat (MIRU-VNTR) identification. Thirty-three were identified as M. avium subsp. avium. These strains were derived from 1 beech marten (Martes foina), 1 common buzzard (Buteo buteo), 2 European badgers (Meles meles), 3 wolves (Canis lupus), and 26 red foxes (Vulpes vulpes). One strain isolated from a wolf was identified as M. avium subsp. hominissuis. The results show the widespread occurrence of MAC bacilli in the studied environment and additionally comprise new data on the molecular characteristics of M. avium subspecies carried by free-living southeastern Polish carnivores.

Targeted and efficient delivery of rifampicin to macrophages involved in non-tuberculous mycobacterial infection via mannosylated solid lipid nanoparticles

Non-tuberculous mycobacterial infections are representative difficult-to-cure lung diseases with high incidence. Conventional treatments have several limitations such as negative side effects and increased drug resistance due to long-term administration. To overcome these limitations, there is a growing need for more stable drug delivery systems. Among the various drug delivery platforms developed thus far, solid lipid nanoparticles can be effectively loaded with hydrophobic substances and their physicochemical properties can be easily manipulated through surface modification, which makes them highly suitable drug delivery materials. Recent studies have reported the successful development of nanoparticles capable of selectively delivering drugs by targeting lectin-like receptors overexpressed on the surface of immune cells. Among these lectin-like receptors, the mannose receptor is a promising target because it is expressed on the surface of macrophages and is involved in immune activity. This study sought to synthesize rifampicin-loaded mannose surface-modified solid lipid nanoparticles (Man-RIF SLNs). The Man-RIF SLN synthesis process was first optimized, after which the characteristics of the synthesized particles were analyzed using dynamic light scattering (DLS), nanoparticle tracking analysis (NTA), and transmission electron microscopy (TEM). The surface modification with mannose was confirmed through FT-IR analysis. More importantly, the synthesized Man-RIF SLNs exhibited antibacterial and anti-biofilm properties against Mycobacterium intracellulare, a causative agent of non-tuberculous lung disease. Therefore, this study demonstrated that mannose receptor-targeted rifampicin delivery through solid lipid nanoparticles can be effectively applied to the treatment of non-tuberculous lung disease. Moreover, Man-RIF SLNs could also be used for the targeted delivery of drugs to several types of carcinoma cells or immune cells, as well as to treat lung diseases.

Additive Effects of Cyclic Peptide [R4W4] When Added Alongside Azithromycin and Rifampicin against Mycobacterium avium Infection

Mycobacterium avium (M. avium), a type of nontuberculous mycobacteria (NTM), poses a risk for pulmonary infections and disseminated infections in immunocompromised individuals. Conventional treatment consists of a 12-month regimen of the first-line antibiotics rifampicin and azithromycin. However, the treatment duration and low antibiotic tolerability present challenges in the treatment of M. avium infection. Furthermore, the emergence of multidrug-resistant mycobacterium strains prompts a need for novel treatments against M. avium infection. This study aims to test the efficacy of a novel antimicrobial peptide, cyclic [R4W4], alongside the first-line antibiotics azithromycin and rifampicin in reducing M. avium survival. Colony-forming unit (CFU) counts were assessed after treating M. avium cultures with varying concentrations of cyclic [R4W4] alone or in conjunction with azithromycin or rifampicin 3 h and 4 days post-treatment. M. avium growth was significantly reduced 4 days after cyclic [R4W4] single treatment. Additionally, cyclic [R4W4]-azithromycin and cyclic [R4W4]-rifampicin combination treatments at specific concentrations significantly reduced M. avium survival 3 h and 4 days post-treatment compared with single antibiotic treatment alone. These findings demonstrate cyclic [R4W4] as a potent treatment method against M. avium and provide insight into novel therapeutic approaches against mycobacterium infections.

Specificity of the innate immune responses to different classes of non-tuberculous mycobacteria

Mycobacterium avium is the most common nontuberculous mycobacterium (NTM) species causing infectious disease. Here, we characterized a M. avium infection model in zebrafish larvae, and compared it to M. marinum infection, a model of tuberculosis. M. avium bacteria are efficiently phagocytosed and frequently induce granuloma-like structures in zebrafish larvae. Although macrophages can respond to both mycobacterial infections, their migration speed is faster in infections caused by M. marinum. Tlr2 is conservatively involved in most aspects of the defense against both mycobacterial infections. However, Tlr2 has a function in the migration speed of macrophages and neutrophils to infection sites with M. marinum that is not observed with M. avium. Using RNAseq analysis, we found a distinct transcriptome response in cytokine-cytokine receptor interaction for M. avium and M. marinum infection. In addition, we found differences in gene expression in metabolic pathways, phagosome formation, matrix remodeling, and apoptosis in response to these mycobacterial infections. In conclusion, we characterized a new M. avium infection model in zebrafish that can be further used in studying pathological mechanisms for NTM-caused diseases.

In vitro assessment of 17 antimicrobial agents against clinical Mycobacterium avium complex isolates

Background

Recently, Mycobacterium avium complex (MAC) infections have been increasing, especially in immunocompromised and older adults. The rapid increase has triggered a global health concern due to limited therapeutic strategies and adverse effects caused by long-term medication. To provide more evidence for the treatment of MAC, we studied the in vitro inhibitory activities of 17 antimicrobial agents against clinical MAC isolates.

Results

A total of 111 clinical MAC isolates were enrolled in the study and they were identified as M. intracellulare, M. avium, M. marseillense, M. colombiense, M. yongonense, and two isolates could not be identified at the species level. MAC strains had relatively low (0–21.6%) resistance to clarithromycin, amikacin, bedaquiline, rifabutin, streptomycin, and clofazimine, and the resistant rates to isoniazid, rifampin, linezolid, doxycycline, and ethionamide were very high (72.1–100%). In addition, M. avium had a significantly higher resistance rate than that of M. intracellulare for ethambutol (92.3% vs 40.7%, P < 0.001), amikacin (15.4% vs 1.2%, P = 0.049), and cycloserine (69.2% vs 25.9%, P = 0.004).

Conclusions

Our results supported the current usage of macrolides, rifabutin, and aminoglycosides in the regimens for MAC infection, and also demonstrated the low resistance rate against new drugs, such as clofazimine, tedizolid, and bedaquiline, suggesting the possible implementation of these drugs in MAC treatment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-022-02582-2.

In silico analysis of promoter regions to identify regulatory elements in TetR family transcriptional regulatory genes of Mycobacterium colombiense CECT 3035

Background

Mycobacterium colombiense is an acid-fast, non-motile, rod-shaped mycobacterium confirmed to cause respiratory disease and disseminated infection in immune-compromised patients, and lymphadenopathy in immune-competent children. It has virulence mechanisms that allow them to adapt, survive, replicate, and produce diseases in the host. To tackle the diseases caused by M. colombiense, understanding of the regulation mechanisms of its genes is important. This paper, therefore, analyzes transcription start sites, promoter regions, motifs, transcription factors, and CpG islands in TetR family transcriptional regulatory (TFTR) genes of M. colombiense CECT 3035 using neural network promoter prediction, MEME, TOMTOM algorithms, and evolutionary analysis with the help of MEGA-X.

Results

The analysis of 22 protein coding TFTR genes of M. colombiense CECT 3035 showed that 86.36% and 13.64% of the gene sequences had one and two TSSs, respectively. Using MEME, we identified five motifs (MTF1, MTF2, MTF3, MTF4, and MTF5) and MTF1 was revealed as the common promoter motif for 100% TFTR genes of M. colombiense CECT 3035 which may serve as binding site for transcription factors that shared a minimum homology of 95.45%. MTF1 was compared to the registered prokaryotic motifs and found to match with 15 of them. MTF1 serves as the binding site mainly for AraC, LexA, and Bacterial histone-like protein families. Other protein families such as MATP, RR, σ-70 factor, TetR, LytTR, LuxR, and NAP also appear to be the binding candidates for MTF1. These families are known to have functions in virulence mechanisms, metabolism, quorum sensing, cell division, and antibiotic resistance. Furthermore, it was found that TFTR genes of M. colombiense CECT 3035 have many CpG islands with several fragments in their CpG islands. Molecular evolutionary genetic analysis showed close relationship among the genes.

Conclusion

We believe these findings will provide a better understanding of the regulation of TFTR genes in M. colombiense CECT 3035 involved in vital processes such as cell division, pathogenesis, and drug resistance and are likely to provide insights for drug development important to tackle the diseases caused by this mycobacterium. We believe this is the first report of in silico analyses of the transcriptional regulation of M. colombiense TFTR genes.

The Role of NRF2 in Mycobacterial Infection

The incidence of pulmonary nontuberculous mycobacterial (NTM) infection is increasing worldwide, and its clinical outcomes with current chemotherapies are unsatisfactory. The incidence of tuberculosis (TB) is still high in Africa, and the existence of drug-resistant tuberculosis is also an important issue for treatment. To discover and develop new efficacious anti-mycobacterial treatments, it is important to understand the host-defense mechanisms against mycobacterial infection. Nuclear erythroid 2 p45-related factor-2 (NRF2) is known to be a major regulator of various antioxidant response element (ARE)-driven cytoprotective gene expressions, and its protective role has been demonstrated in infections. However, there are not many papers or reviews regarding the role of NRF2 in mycobacterial infectious disease. Therefore, this review focuses on the role of NRF2 in the pathogenesis of Mycobacterium tuberculosis and Mycobacterium avium infection.

Mycobacterium avium Subsp. hominissuis Interactions with Macrophage Killing Mechanisms

Non-tuberculosis mycobacteria (NTM) are ubiquitously found throughout the environment. NTM can cause respiratory infections in individuals with underlying lung conditions when inhaled, or systemic infections when ingested by patients with impaired immune systems. Current therapies can be ineffective at treating NTM respiratory infections, even after a long course or with multidrug treatment regimens. NTM, such as Mycobacterium avium subspecies hominissuis (M. avium), is an opportunistic pathogen that shares environments with ubiquitous free-living amoeba and other environmental hosts, possibly their evolutionary hosts. It is highly likely that interactions between M. avium and free-living amoeba have provided selective pressure on the bacteria to acquire survival mechanisms, which are also used against predation by macrophages. In macrophages, M. avium resides inside phagosomes and has been shown to exit it to infect other cells. M. avium's adaptation to the hostile intra-phagosomal environment is due to many virulence mechanisms. M. avium is able to switch the phenotype of the macrophage to be anti-inflammatory (M2). Here, we have focused on and discussed the bacterial defense mechanisms associated with the intra-phagosome phase of infection. M. avium possesses a plethora of antioxidant enzymes, including the superoxide dismutases, catalase and alkyl hydroperoxide reductase. When these defenses fail or are overtaken by robust oxidative burst, many other enzymes exist to repair damage incurred on M. avium proteins, including thioredoxin/thioredoxin reductase. Finally, M. avium has several oxidant sensors that induce transcription of antioxidant enzymes, oxidation repair enzymes and biofilm- promoting genes. These expressions induce physiological changes that allow M. avium to survive in the face of leukocyte-generated oxidative stress. We will discuss the strategies used by M. avium to infect human macrophages that evolved during its evolution from free-living amoeba. The more insight we gain about M. avium's mode of pathogenicity, the more targets we can have to direct new anti-virulence therapies toward.