Virulence and immune response induced by Mycobacterium avium complex strains in a model of progressive pulmonary tuberculosis and subcutaneous infection in BALB/c mice

Effect of IL-17A on the immune response to pulmonary tuberculosis induced by high- and low-virulence strains of Mycobacterium bovis

Tuberculosis (TB) is an infectious, chronic, and progressive disease occurring globally. Human TB is caused mainly by Mycobacterium tuberculosis (M. tuberculosis), while the main causative agent of bovine TB is Mycobacterium bovis (M. bovis). The latter is one of the most important cattle pathogens and is considered the main cause of zoonotic TB worldwide. The mechanisms responsible for tissue damage (necrosis) during post-primary TB remain elusive. Recently, IL-17A was reported to be important for protection against M. tuberculosis infection, but it is also related to the production of an intense inflammatory response associated with necrosis. We used two M. bovis isolates with different levels of virulence and high IL-17A production to study this important cytokine's contrasting functions in a BALB/c mouse model of pulmonary TB. In the first part of the study, the gene expression kinetics and cellular sources of IL-17A were determined by real time PCR and immunohistochemistry respectively. Non-infected lungs showed low production of IL-17A, particularly by the bronchial epithelium, while lungs infected with the low-virulence 534 strain showed high IL-17A expression on Day 3 post-infection, followed by a decrease in expression in the early stage of the infection and another increase during late infection, on Day 60, when very low bacillary burdens were found. In contrast, infection with the highly virulent strain 04-303 induced a peak of IL-17A expression on Day 14 of infection, 1 week before extensive pulmonary necrosis was seen, being lymphocytes and macrophages the most important sources. In the second part of the study, the contribution of IL-17A to immune protection and pulmonary necrosis was evaluated by suppressing IL-17A via the administration of specific blocking antibodies. Infection with M. bovis strain 534 and treatment with IL-17A neutralizing antibodies did not affect mouse survival but produced a significant increase in bacillary load and a non-significant decrease in inflammatory infiltrate and granuloma area. In contrast, mice infected with the highly virulent 04-303 strain and treated with IL-17A blocking antibodies showed a significant decrease in survival, an increase in bacillary loads on Day 24 post-infection, and significantly more and earlier necrosis. Our results suggest that high expression of IL-17A is more related to protection than necrosis in a mouse model of pulmonary TB induced by M. bovis strains.

Comparative genome analysis reveals high-level drug resistance markers in a clinical isolate of Mycobacterium fortuitum subsp. fortuitum MF GZ001

Introduction

Infections caused by non-tuberculosis mycobacteria are significantly worsening across the globe. M. fortuitum complex is a rapidly growing pathogenic species that is of clinical relevance to both humans and animals. This pathogen has the potential to create adverse effects on human healthcare.

Methods

The MF GZ001 clinical strain was collected from the sputum of a 45-year-old male patient with a pulmonary infection. The morphological studies, comparative genomic analysis, and drug resistance profiles along with variants detection were performed in this study. In addition, comparative analysis of virulence genes led us to understand the pathogenicity of this organism.

Results

Bacterial growth kinetics and morphology confirmed that MF GZ001 is a rapidly growing species with a rough morphotype. The MF GZ001 contains 6413573 bp genome size with 66.18 % high G+C content. MF GZ001 possesses a larger genome than other related mycobacteria and included 6156 protein-coding genes. Molecular phylogenetic tree, collinearity, and comparative genomic analysis suggested that MF GZ001 is a novel member of the M. fortuitum complex. We carried out the drug resistance profile analysis and found single nucleotide polymorphism (SNP) mutations in key drug resistance genes such as rpoB, katG, AAC(2')-Ib, gyrA, gyrB, embB, pncA, blaF, thyA, embC, embR, and iniA. In addition, the MF GZ001strain contains mutations in iniA, iniC, pncA, and ribD which conferred resistance to isoniazid, ethambutol, pyrazinamide, and para-aminosalicylic acid respectively, which are not frequently observed in rapidly growing mycobacteria. A wide variety of predicted putative potential virulence genes were found in MF GZ001, most of which are shared with well-recognized mycobacterial species with high pathogenic profiles such as M. tuberculosis and M. abscessus.

Discussion

Our identified novel features of a pathogenic member of the M. fortuitum complex will provide the foundation for further investigation of mycobacterial pathogenicity and effective treatment.

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.

Factors Associated with Treatment Outcome in Patients with Nontuberculous Mycobacterial Pulmonary Disease: A Large Population-Based Retrospective Cohort Study in Shanghai

Infectious diseases caused by nontuberculous mycobacteria (NTM) are increasingly common. This retrospective cohort study examined factors associated with outcomes in patients from Shanghai who had NTM pulmonary disease (NTMPD) from January 2014 to December 2018. The causative bacterial species, drug susceptibility test results, treatment outcomes, sputum culture conversion rate, and risk factors associated with treatment failure were determined. The most common species were Mycobacterium avium complex (MAC) (50%), M. abscessus (28%), and M. kansasii (15%). Over five years, the proportions of M. kansasii and M. abscessus increased, and that of MAC decreased. The treatment success rate was significantly greater for patients infected with M. kansasii (89.9%) than MAC (65.0%, p < 0.001) and M. abscessus (36.1%, p < 0.001). Multivariate analysis indicated the risk factors for treatment failure were pathogenic NTM species (M. abscessus: aOR = 9.355, p < 0.001; MAC: aOR = 2.970, p < 0.001), elevated ESR (>60 mm/h: aOR = 2.658, p < 0.001), receipt of retreatment (aOR = 2.074, p < 0.001), and being middle-aged or elderly (>60 years-old: aOR = 1.739, p = 0.021; 45-60 years-old: aOR = 1.661, p = 0.034). The main bacterial species responsible for NTMPD were MAC, M. abscessus, and M. kansasii. Patients who were infected by M. abscessus or MAC, with elevated ESR, received retreatment, and were middle-aged or elderly had an increased risk of treatment failure.

Mutation on lysX from Mycobacterium avium hominissuis impacts the host-pathogen interaction and virulence phenotype

The lysX gene from Mycobacterium avium hominissuis (MAH) is not only involved in cationic antimicrobial resistance but also regulates metabolic activity. An MAH lysX deficient mutant was shown to exhibit a metabolic shift at the extracellular state preadapting the bacteria to the conditions inside host-cells. It further showed stronger growth in human monocytes. In the present study, the LysX activity on host-pathogen interactions were analyzed. The lysX mutant from MAH proved to be more sensitive toward host-mediated stresses such as reactive oxygen species. Further, the lysX mutant exhibited increased inflammatory response in PBMC and multinucleated giant cell (MGC) formation in human macrophages during infection studies. Coincidentally, the lysX mutant strain revealed to be more reproductive in the Galleria mellonella infection model. Together, these data demonstrate that LysX plays a role in regulating the bacillary load in host organisms and the lack of lysX gene facilitates MAH adaptation to intracellular host-habitat, thereby suggesting an essential role of LysX in the modulation of host-pathogen interaction.

Characterization of integrated prophages within diverse species of clinical nontuberculous mycobacteria

BACKGROUND

Nontuberculous mycobacterial (NTM) infections are increasing in prevalence, with current estimates suggesting that over 100,000 people in the United States are affected each year. It is unclear how certain species of mycobacteria transition from environmental bacteria to clinical pathogens, or what genetic elements influence the differences in virulence among strains of the same species. A potential mechanism of genetic evolution and diversity within mycobacteria is the presence of integrated viruses called prophages in the host genome. Prophages may act as carriers of bacterial genes, with the potential of altering bacterial fitness through horizontal gene transfer. In this study, we quantify the frequency and composition of prophages within mycobacteria isolated from clinical samples and compare them against the composition of PhagesDB, an environmental mycobacteriophage database.

METHODS

Prophages were predicted by agreement between two discovery tools, VirSorter and Phaster, and the frequencies of integrated prophages were compared by growth rate. Prophages were assigned to PhagesDB lettered clusters. Bacterial virulence gene frequency was calculated using a combination of the Virulence Factor Database (VFDB) and the Pathosystems Resource Integration Center virulence database (Patric-VF) within the gene annotation software Prokka. CRISPR elements were discovered using CRT. ARAGORN was used to quantify tRNAs.

RESULTS

Rapidly growing mycobacteria (RGM) were more likely to contain prophage than slowly growing mycobacteria (SGM). CRISPR elements were not associated with prophage abundance in mycobacteria. The abundance of tRNAs was enriched in SGM compared to RGM. We compared the abundance of bacterial virulence genes within prophage genomes from clinical isolates to mycobacteriophages from PhagesDB. Our data suggests that prophages from clinical mycobacteria are enriched for bacterial virulence genes relative to environmental mycobacteriophage from PhagesDB.

CONCLUSION

Prophages are present in clinical NTM isolates. Prophages are more likely to be present in RGM compared to SGM genomes. The mechanism and selective advantage of this enrichment by growth rate remain unclear. In addition, the frequency of bacterial virulence genes in prophages from clinical NTM is enriched relative to the PhagesDB environmental proxy. This suggests prophages may act as a reservoir of genetic elements bacteria could use to thrive within a clinical environment.

A case report of disseminated Mycobacterium colombiense infection in an HIV patient

Mycobacterium colombiense is a newly recognized member of the Mycobacterium avium complex, and only a few cases of infections caused by this pathogen have been reported. We present an imported case of disseminated disease caused by M. colombiense in an HIV patient in early February 2017.

Circulation of M. tuberculosis Beijing genotype in Latin America and the Caribbean

Lineage 2 (East Asian), which includes the Beijing genotype, is one of the most prevalent lineages of Mycobacterium tuberculosis (Mtb) throughout the world. The Beijing family is associated to hypervirulence and drug-resistant tuberculosis. The study of this genotype's circulation in Latin America is crucial for achieving total control of TB, the goal established by the World Health Organization, for the American sub-continent, before 2035. In this sense, the present work presents an overview of the status of the Beijing genotype for this region, with a bibliographical review, and data analysis of MIRU-VNTRs for available Beijing isolates. Certain countries present a prevalent trend of <5%, suggesting low transmissibility for the region, with the exception of Cuba (17.2%), Perú (16%) and Colombia (5%). Minimum Spanning Tree analysis, obtained from MIRU-VNTR data, shows distribution of specific clonal complex strains in each country. From this data, in most countries, we found that molecular epidemiology has not been a tool used for the control of TB, suggesting that the Beijing genotype may be underestimated in Latin America. It is recommended that countries with the highest incidence of the Beijing genotype use effective control strategies and increased care, as a requirement for public health systems.

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.

Dual role of hypoxia-inducible factor 1 α in experimental pulmonary tuberculosis: its implication as a new therapeutic target

AIM

Investigate the role of hypoxia-inducible factor-1α (HIF-1α) in pulmonary tuberculosis (TB).

METHODS & RESULTS

A model of progressive pulmonary TB in BALB/c mice, immunohistochemistry and digital pathology were used. High HIF-1α expression was observed during early TB in activated macrophages. During late TB, even higher HIF-1α expression was observed in foamy macrophages, which are resistant to apoptosis. Blocking HIF-1α during early infection with 2-methoxyestradiol worsened the disease, while during late TB, it induced macrophage apoptosis and decreased bacillary loads.

CONCLUSION

HIF-1α has a dual role in experimental TB. This finding could have therapeutic implications because combined treatment with 2-methoxyestradiol and antibiotics appeared to eliminate mycobacteria more efficiently than conventional chemotherapy during advanced disease.

Natural history of Mycobacterium avium complex lung disease in untreated patients with stable course

Little is known about the long-term natural history of Mycobacterium avium complex lung disease (MAC-LD) in untreated patients with stable course.The aim of this study was to investigate the natural course of untreated stable MAC-LD, with a focus on factors associated with clinical deterioration, spontaneous sputum conversion and prognosis.Of 488 patients diagnosed with MAC-LD between 1998 and 2011, 305 patients (62.5%) showed progressive MAC-LD resulting in treatment initiation within 3 years of diagnosis and 115 patients (23.6%) exhibited stable MAC-LD for at least 3 years with a median follow-up duration of 5.6 years. Patients with stable MAC-LD were more likely to have higher body mass index and less systemic symptoms at initial diagnosis compared with patients with progressive MAC-LD, while positive sputum acid-fast bacilli smear, fibrocavitary type and more extensive disease in radiological findings were more associated with progressive MAC-LD. Of the untreated patients with stable MAC-LD, 51.6% underwent spontaneous sputum conversion, with younger age, higher body mass index and negative sputum acid-fast bacilli smear at initial diagnosis found to be predictors of this occurrence.Advanced age, fibrocavitary type and abnormal pulmonary function were negative prognostic factors for survival in patients with stable MAC-LD.

Deciphering the virulence factors of the opportunistic pathogen Mycobacterium colombiense

Mycobacterium avium complex (MAC) contains clinically important nontuberculous mycobacteria worldwide and is the second largest medical complex in the Mycobacterium genus after the Mycobacterium tuberculosis complex. MAC comprises several species that are closely phylogenetically related but diverse regarding their host preference, course of disease, virulence and immune response. In this study we provided immunologic and virulence-related insights into the M. colombiense genome as a model of an opportunistic pathogen in the MAC. By using bioinformatic tools we found that M. colombiense has deletions in the genes involved in p-HBA/PDIM/PGL, PLC, SL-1 and HspX production, and loss of the ESX-1 locus. This information not only sheds light on our understanding the virulence mechanisms used by opportunistic MAC pathogens but also has great potential for the designing of species-specific diagnostic tools.

Inverse correlation between salt tolerance and host-adaptation in mycobacteria

BACKGROUND

The genus Mycobacterium includes host-adapted organisms regarded as obligate and opportunistic pathogens and environmental organisms. Factors contributing to this wide range of adaptations are poorly known.

RESULTS

We studied the salt tolerance of 46 Mycobacterium species of medical interest. Representative strains of the Mycobacterium tuberculosis complex, Mycobacterium avium complex, Mycobacterium chelonae-abscessus complex, Mycobacterium ulcerans, Mycobacterium marinum, Mycobacterium lentiflavum, Mycobacterium fortuitum and Mycobacterium conceptionense were inoculated on Middlebrook 7H10 medium supplemented with 0-10% sodium chloride. Colonies were counted after 2-4 week incubation at the appropriate 30-37 °C temperature depending on the tested strain. Further comparative genomics was done on 15 Mycobacterium strains representing the spectrum of salt-tolerance of mycobacteria. Based on the results the different species were grouped according to their salt tolerance into a "salt-sensitive" group (growth up to ≤3% salt) containing the M. tuberculosis complex, Mycobacterium chelonae, Mycobacterium lentiflavum, Mycobacterium ulcerans and Mycobacterium marinum; a "salt-intermediate" group (growth between 4 and 6% salt) comprising Mycobacterium avium, Mycobacterium intracellulare, Mycobacterium chimaera and a "salt-resistant" group (growth up to >6%) comprising Mycobacterium homonissuis, Mycobacterium bolettii, Mycobacterium fortuitum and Mycobacterium conceptionense. Genomic analysis revealed that 290 genes were unique to species belonging to the salt-sensitive group; and that 15% were annotated as being functionally associated with the ESX secretion systems Pro-Glu and Pro-Pro-Glu family proteins.

CONCLUSIONS

In this work we found an inverse correlation between salt tolerance and host adaptation. We thus propose that salinity is one of the multiple factors determining the ecological niches of mycobacteria.

A novel role of Yin-Yang-1 in pulmonary tuberculosis through the regulation of the chemokine CCL4

Mycobacterium tuberculosis (M. tb) is the etiological agent of pulmonary tuberculosis (TB); this disease remains a worldwide health problem. Yin-Yang-1 (YY1) plays a major role in the maintenance and progression of some pulmonary diseases, including pulmonary fibrosis. However, the role of YY1 in TB remains unknown. The aim of this study was to elucidate the role of YY1 in the regulation of CCL4 and its implication in TB. We determined whether YY1 regulates CCL4 using reporter plasmids, ChIP and siRNA assays. Immunohistochemistry and digital pathology were used to measure the expression of YY1 and CCL4 in a mouse model of TB. A retrospective comparison of patients with TB and control subjects was used to measure the expression of YY1 and CCL4 using tissue microarrays. Our results showed that YY1 regulates the transcription of CCL4; moreover, YY1, CCL4 and TGF-β were overexpressed in the lung tissues of mice with TB during the late stages of the disease and the tissues of TB patients. The expression of CCL4 and TGF-β correlated with YY1 expression. In conclusion, YY1 regulates CCL4 transcription; moreover, YY1 is overexpressed in experimental and human TB and is positively correlated with CCL4 and TGF-β expression. Therefore, treatments that decrease YY1 expression may be a new therapeutic strategy against TB.

Type II interferon promotes differentiation of myeloid-biased hematopoietic stem cells

Interferon gamma (IFNγ) promotes cell division of hematopoietic stem cells (HSCs) without affecting the total HSC number. We postulated that IFNγ stimulates differentiation of HSCs as part of the innate immune response. Here, we report that type II interferon signaling is required, both at baseline and during an animal model of LCMV infection, to maintain normal myeloid development. By separately evaluating myeloid-biased and lymphoid-biased HSC subtypes, we found that myeloid-biased HSCs express higher levels of IFNγ receptor and are specifically activated to divide after recombinant IFNγ exposure in vivo. While both HSC subtypes show increased expression of the transcription factor C/EBPβ after infection, only the myeloid-biased HSCs are transiently depleted from the marrow during the type II interferon-mediated immune response to Mycobacterium avium infection, as measured both functionally and phenotypically. These findings indicate that IFNγ selectively permits differentiation of myeloid-biased HSCs during an innate immune response to infection. This represents the first report of a context and a mechanism for discriminate utilization of the alternate HSC subtypes. Terminal differentiation, at the expense of self-renewal, may compromise HSC populations during states of chronic inflammation.

Molecular Identification of Mycobacterium Species of Public Health Importance in Cattle in Zimbabwe by 16S rRNA Gene Sequencing

Mycobacterium species are naturally found in the environment as well as in domestic animals such as cattle. So far, more than 150 species of Mycobacterium, some of which are pathogenic, have been identified. Laboratory isolation, detection and identification of Mycobacterium species are therefore critical if human and animal infections are to be controlled. The objective of this study was to identify Mycobacterium species isolated in cattle in Zimbabwe using 16S ribosomal RNA gene amplification and sequencing. A total of 134 cow dung samples were collected throughout Zimbabwe and mycobacteria were isolated by culture. Only 49 culture isolates that were found to be acid-fast bacilli positive by Ziehl-Neelsen staining. The 16S rRNA gene was successfully amplified by PCR in 41 (84%) of the samples. There was no amplification in 8 (16%) of the samples. Out of the 41 samples that showed amplification, 26 (63%) had strong PCR bands and were selected for DNA sequencing. Analysis of the DNA sequences showed that 7 (27%) belonged to Mycobacterium neoaurum, 6 (23%) belonged to Mycobacterium fortuitum, 3 (12%) to Mycobacterium goodii, 2 (1%) to Mycobacterium arupense, 2 (1%) to Mycobacterium peregrinum or M. septicum and 1 isolate (0.04%) to Mycobacterium elephantis. There were 5 (19%) isolates that were non-mycobacteria and identified as Gordonia terrae, a close relative of Mycobacterium. The study therefore provided a molecular basis for detection and identification of Mycobacterium species in animals and humans.

Restoration of innate immune activation accelerates Th1-cell priming and protection following pulmonary mycobacterial infection

The immune mechanisms underlying delayed induction of Th1-type immunity in the lungs following pulmonary mycobacterial infection remain poorly understood. We have herein investigated the underlying immune mechanisms for such delayed responses and whether a selected innate immune-modulating strategy can accelerate Th1-type responses. We have found that, in the early stage of pulmonary infection with attenuated Mycobacterium tuberculosis (M.tb H37Ra), the levels of infection in the lung continue to increase logarithmically until days 14 and 21 postinfection in C57BL/6 mice. The activation of innate immune responses, particularly DCs, in the lung is delayed. This results in a delay in the subsequent downstream immune responses including the migration of antigen-bearing DCs to the draining lymph node (dLN), the Th1-cell priming in dLN, and the recruitment of Th1 cells to the lung. However, single lung mucosal exposure to the TLR agonist FimH postinfection is able to accelerate protective Th1-type immunity via facilitating DC migration to the lung and draining lymph nodes, enhancing DC antigen presentation and Th1-cell priming. These findings hold implications for the development of immunotherapeutic and vaccination strategies and suggest that enhancement of early innate immune activation is a viable option for improving Th1-type immunity against pulmonary mycobacterial diseases.