Coinfection by Mycobacterium marinum and Mycolicibacterium fortuitum in a captive adult diamondback water snake causing disseminated mycobacteriosis with acute cutaneous ulceration.

An adult male captive diamondback water snake (Nerodia rhombifer) was found dead after a 1-d history of lethargy and cutaneous ulcers. The snake had eaten 2 sunfish (Mola spp.) 5 d before death. Gross examination revealed white-to-tan nodules in the lung and liver and segmental intestinal impactions with digested fish. Histopathology confirmed disseminated granulomas with numerous intrahistiocytic acid-fast bacteria in the skin, skeletal muscle, lung, liver, and intestines. Mycobacterium marinum and Mycolicibacterium fortuitum were identified by culture of the hepatic granuloma, followed by PCR and rpoB gene sequencing. To our knowledge, this is the first description of M. marinum and M. fortuitum coinfection in this species. Although M. fortuitum has been isolated from reptiles, lesions associated with its presence in tissues have not been described previously. Interestingly, the mineralization within granulomas that we observed in our case is not reported in mycobacterial infection in reptiles, whereas this finding is common in mammals.

Temporal and cellular analysis of granuloma development in mycobacterial infected adult zebrafish.

Because granulomas are a hallmark of tuberculosis pathogenesis, the study of the dynamic changes in their cellular composition and morphological character can facilitate our understanding of tuberculosis pathogenicity. Adult zebrafish infected with Mycobacterium marinum form granulomas that are similar to the granulomas in human patients with tuberculosis and therefore have been used to study host-mycobacterium interactions. Most studies of zebrafish granulomas, however, have focused on necrotic granulomas, while a systematic description of the different stages of granuloma formation in the zebrafish model is lacking. Here, we characterized the stages of granulomas in M. marinum-infected zebrafish, including early immune cell infiltration, nonnecrotizing granulomas, and necrotizing granulomas, using corresponding samples from patients with pulmonary tuberculosis as references. We combined hematoxylin and eosin staining and in situ hybridization to identify the different immune cell types and follow their spatial distribution in the different stages of granuloma development. The macrophages in zebrafish granulomas were shown to belong to distinct subtypes: epithelioid macrophages, foamy macrophages, and multinucleated giant cells. By defining the developmental stages of zebrafish granulomas and the spatial distribution of the different immune cells they contain, this work provides a reference for future studies of mycobacterial granulomas and their immune microenvironments.

An Oxygen Supply Strategy for Sonodynamic Therapy in Tuberculous Granuloma Lesions Using a Catalase-Loaded Nanoplatform.

Purpose: Tuberculosis (TB) is a chronic disease caused by Mycobacterium tuberculosis (MTB) that remains a major global health challenge. One of the main obstacles to effective treatment is the heterogeneous microenvironment of TB granulomas. This study aimed to investigate the potential of a hypoxic remission-based strategy to enhance the outcome of tuberculosis treatment when implemented in combination with ultrasound. Methods: A PLGA nanoparticle (LEV@CAT-NPs) loaded with levofloxacin (LEV) and catalase (CAT) was fabricated by a double emulsification method, and its physical characteristics, oxygen production capacity, drug release capacity, and biosafety were thoroughly investigated. The synergistic therapeutic effects of ultrasound (US)-mediated LEV@CAT-NPs were evaluated using an experimental mouse model of subcutaneous tuberculosis granuloma induced by Bacille Calmette-Guérin (BCG) as a substitute for MTB. Results: LEV@CAT-NPs exhibited excellent oxygen production capacity, biosafety, and biocompatibility. Histological analysis revealed that ultrasound-mediated LEV@CAT-NPs could effectively remove bacteria from tuberculous granulomas, significantly alleviate the hypoxia state, reduce the necrotic area and inflammatory cells within the granuloma, and increase the penetration of dyes in granuloma tissues. The combined treatment also reduced the serum levels of inflammatory cytokines (eg, TNF-α, IL-6, and IL-8), and significantly downregulated the expression of hypoxia-inducible factor 1α (HIF-1α) and vascular endothelial growth factor (VEGF). These results suggested that the synergistic treatment of ultrasound-mediated LEV@CAT-NPs effectively eradicated the bacterial infection and reversed the hypoxic microenvironment of tuberculous granulomas, further promoting tissue repair. Conclusion: This study provides a non-invasive and new avenue for treating refractory tuberculosis infections. The potential role of regulating hypoxia within infected lesions as a therapeutic target for infection deserves further exploration in future studies.

Monitoring the immune response of macrophages in tuberculous granuloma through the expression of CD68, iNOS and HLA-DR in naturally infected beef cattle.

Bovine tuberculosis still represents a universal threat that creates a wider range of public and animal health impacts. One of the most important steps in the pathogenesis of this disease and granuloma formation is the phagocytosis of tuberculous bacilli by macrophages. Mycobacteria replicate in macrophages, which are crucial to the pathophysiology of mycobacterial infections; however, scarce information is available about the dynamics of the granuloma-stage immunological response. Therefore, immunohistochemistry was used in this work to evaluate the expression of CD68, iNOS, and HLA-DR in different stages of TB granulomas from naturally infected cattle with tuberculosis. Two thousand, one hundred and fifty slaughtered beef cattle were examined during the period from September 2020 to March 2022. Sixty of them showed gross tuberculous pulmonary lesions and samples were collected from all of them for histopathological examination, Ziehl-Neelsen (ZN) staining, and bacteriological culturing. Selected samples that yielded a positive result for ZN and mycobacterial culturing were subjected to an immunohistochemical study of CD68, iNOS, and HLA-DR expression by macrophages according to granuloma stages. Immunohistochemical analysis revealed that the immunolabeling of CD68+, iNOS+, and HLA-DR+ macrophages significantly reduced as the stage of granuloma increased from stage I to stage IV (P < 0.003, P < 0.002, and P < 0.002, respectively). The distribution of immunolabeled macrophages was similar for the three markers, with immunolabeled macrophages distributed throughout early-stage granulomas (I, II), and surrounding the necrotic core in late-stage granulomas (III, IV). Our results suggest a polarization to the pro-inflammatory environment and increased expression of CD68+, iNOS+, and HLA-DR+ macrophages in the early stages of granulomas (I, II), which may play a protective role in the immune response of naturally infected beef cattle with tuberculosis.

Evaluation of incidence, predictive factors and treatment considerations for asymptomatic genitourinary granulomas after intravesical bacillus Calmette-Guérin therapy.

INTRODUCTION AND OBJECTIVES: Although the complications of intravesical BCG treatment are well described, asymptomatic genitourinary granulomas after BCG therapy have rarely been reported and management strategy for these conditions remains controversial. The objective of this study is to evaluate the incidence rate of asymptomatic genitourinary granuloma formation mimicking bladder cancer recurrence after intravesical bacillus Calmette-Guérin (BCG) therapy and to identify the diagnostic and treatment strategies according to patient conditions. PATIENTS AND METHODS: A retrospective review was conducted on 162 patients who underwent intravesical BCG therapy. For patients who developed granulomas, we evaluated the time interval between BCG instillation and the development of granuloma, the presence of acid-fast bacteria on pathology specimens, culture/polymerase chain reaction results, management strategies for the lesions, and clinical outcomes. RESULTS: Asymptomatic genitourinary masses developed in 14 patients, of whom 5 underwent histological examinations and all were confirmed to have granulomatous inflammation. The affected organs included the kidney, bladder, prostate, and penis. While four of the five patients did not receive treatment for their granulomas, one patient was administered antituberculous medication to prevent worsening of the lesion during the perioperative period of the scheduled cystoprostatectomy. None of the patients experienced worsening or recurrence of granulomatous lesions. Patients who developed asymptomatic masses (n = 14) were significantly younger than those who did not (p = 0.0076) and multivariate analysis also showed that younger age was independently associated with the development of clinically suspicious lesions (p = 0.032); however, none of the parameters were associated with histologically confirmed granuloma formation. CONCLUSIONS: Genitourinary granulomas mimicking recurrence of carcinoma may develop in nearly 10% of patients after intravesical BCG therapy. Most patients can be managed without potentially toxic antituberculosis therapy.

Canine leproid granuloma caused by a member of the Mycobacterium tuberculosis complex.

Canine leproid granuloma (CLG) is a chronic form of dermatitis that has been associated with nontuberculous mycobacterial infections in Africa, Oceania, the Americas, and Europe. We report here a case of CLG associated with a member of the Mycobacterium tuberculosis complex (MTBC), which could be of public health concern. An 8-y-old pet dog developed 0.5-1-cm diameter, raised, firm, nonpruritic, alopecic, painless skin nodules on the external aspects of both pinnae. Histologic examination revealed severe pyogranulomatous dermatitis with intracellular Ziehl-Neelsen-positive bacilli that were immunoreactive by immunohistochemistry using a polyclonal primary antibody that recognizes tuberculous and nontuberculous Mycobacterium species. DNA extracted from formalin-fixed, paraffin-embedded skin sections was tested by a Mycobacterium genus-specific nested PCR assay targeting the 16S rRNA gene. BLAST sequence analysis of 214-bp and 178-bp amplicons showed 99.5% identity with members of the MTBC; however, the agent could not be identified at the species level. Although CLG has been associated traditionally with nontuberculous mycobacterial infections, the role of Mycobacterium spp. within the MTBC as a cause of this condition, and the role of dogs with CLG as possible sources of MTBC to other animals and humans, should not be disregarded given its zoonotic potential.

Spatial multiomic profiling reveals the novel polarization of foamy macrophages within necrotic granulomatous lesions developed in lungs of C3HeB/FeJ mice infected with Mycobacterium tuberculosis.

Infection with Mycobacterium tuberculosis leads to the development of tuberculosis (TB) with the formation of granulomatous lesions. Foamy macrophages (FM) are a hallmark of TB granulomas, because they provide the primary platform of M. tuberculosis proliferation and the main source of caseous necrosis. In this study, we applied spatial multiomic profiling to identify the signatures of FM within the necrotic granulomas developed in a mouse model resembling human TB histopathology. C3HeB/FeJ mice were infected with M. tuberculosis to induce the formation of necrotic granulomas in the lungs. Using laser microdissection, necrotic granulomas were fractionated into three distinct regions, including the central caseous necrosis, the rim containing FM, and the peripheral layer of macrophages and lymphocytes, and subjected to proteomic and transcriptomic analyses. Comparison of proteomic and transcriptomic analyses of three distinct granulomatous regions revealed that four proteins/genes are commonly enriched in the rim region. Immunohistochemistry confirmed the localization of identified signatures to the rim of necrotic granulomas. We also investigated the localization of the representative markers for M1 macrophages in granulomas because the signatures of the rim included M2 macrophage markers. The localization of both macrophage markers suggests that FM in necrotic granulomas possessed the features of M1 or M2 macrophages. Gene set enrichment analysis of transcriptomic profiling revealed the upregulation of genes related to M2 macrophage activation and mTORC1 signaling in the rim. These results will provide new insights into the process of FM biogenesis, leading to further understanding of the pathophysiology of TB granulomas.

Muscular pseudotumor revealing a mycobacterial granuloma after bacillus Calmette-Guérin therapy.

INTRODUCTION: The Bacillus Calmette-Guérin (BCG) is a live attenuated strain of Mycobacterium bovis. Intravesical therapy with BCG has long been proved to be effective in treating early-stage bladder carcinoma. CASE REPORT: A 81-year-old male patient with former history of BCG instillations for bladder cancer two years ago was admitted in February 2020 to our department for a pulsatile and painful tumefaction of the right thigh that lasted for 6 months, due to a muscular M. bovis granuloma leading to femoral artery erosion. Emergency vascular surgery associated with prolonged antibiotherapy provided full recovery. DISCUSSION: Late infectious complications of intravesical BCG instillations are classical but rare. Isolated muscular involvement is exceptional. CONCLUSION: Mycobacterial infection should be carefully screened face to a granuloma presenting as muscular pseudotumor. A history of BCG therapy, even decades earlier, enhances this hypothesis and should lead to enforce microbiological testing, especially molecular test.

Different modalities of host cell death and their impact on Mycobacterium tuberculosis infection.

Mycobacterium tuberculosis (Mtb) is the pathogen that causes tuberculosis (TB), a leading infectious disease of humans worldwide. One of the main histopathological hallmarks of TB is the formation of granulomas comprised of elaborately organized aggregates of immune cells containing the pathogen. Dissemination of Mtb from infected cells in the granulomas due to host and mycobacterial factors induces multiple cell death modalities in infected cells. Based on molecular mechanism, morphological characteristics, and signal dependency, there are two main categories of cell death: programmed and nonprogrammed. Programmed cell death (PCD), such as apoptosis and autophagy, is associated with a protective response to Mtb by keeping the bacteria encased within dead macrophages that can be readily phagocytosed by arriving in uninfected or neighboring cells. In contrast, non-PCD necrotic cell death favors the pathogen, resulting in bacterial release into the extracellular environment. Multiple types of cell death in the PCD category, including pyroptosis, necroptosis, ferroptosis, ETosis, parthanatos, and PANoptosis, may be involved in Mtb infection. Since PCD pathways are essential for host immunity to Mtb, therapeutic compounds targeting cell death signaling pathways have been experimentally tested for TB treatment. This review summarizes different modalities of Mtb-mediated host cell deaths, the molecular mechanisms underpinning host cell death during Mtb infection, and its potential implications for host immunity. In addition, targeting host cell death pathways as potential therapeutic and preventive approaches against Mtb infection is also discussed.

Extracellular matrix proteins (fibronectin, collagen III, and collagen I) immunoexpression in goat tuberculous granulomas (Mycobacterium caprae).

The lesion resulting from the interaction between Mycobacterium and the host immune response is the tuberculous granuloma. Tuberculous granulomas, except in incipient stages, are partially or totally encapsulated by connective tissue. The aim of this study was to assess the immunoexpression of the extracellular matrix proteins fibronectin, collagen III, and collagen I in granulomas caused by Mycobacterium caprae in goats (Capra aegagrus hircus) to understand capsule development at different granuloma stages. For this purpose, a retrospective study of 56 samples of tuberculous granulomas in lung (n = 30) and mediastinal lymph node (n = 26) from 17 goats naturally infected with M. caprae in stages I (n = 15), II (n = 14) and III (n = 27) was carried out. Fibronectin immunoreaction was extracellular, fibrillar-reticular in the center of stage I, II and III granulomas and peripheral in stages II and III granulomas. Collagen III immunoexpression was extracellular and fibrillar in the center of stages I, II and III tuberculous granulomas in lung and mediastinal lymph node, and progressive expression was observed in the periphery of stages II and III granulomas. Finally, collagen I immunoexpression was extracellular and fibrillar, showing a progressive loss of central expression and an increase in peripheral expression in stage III granulomas compared to stage I granulomas. Immunoexpression of these extracellular matrix proteins could help understand fibrogenesis and dating in tuberculous granuloma in both animal models and humans.

Tuberculosis in free-ranging and captive wild animals: Pathological and molecular diagnosis with histomorphological differentiation of granulomatous lesions.

Tuberculosis (TB) is a serious zoonotic threat, impacting the human-livestock-wildlife interface globally. Here, we evaluated the status and histomorphological differentiation of TB lesions in 89 morbid cases of wild animals (bovids, cervids, carnivores, non-human primates, and pachyderms) in India. Histomorphological and molecular studies were done using Ziehl-Neelsen (ZN) staining, immunohistochemistry, and polymerase chain reaction (PCR), whereas cultural isolation was performed on selected samples. A total of 32 (35.95%) cases were confirmed as TB, comprising of 12 carnivores, 09 bovids, 06 cervids, 04 non-human primates, and a pachyderm. The TB lesions in the lungs, liver, and lymph nodes varied from the large-sized caseous nodules filled with dry cheesy material in bovids and cervids to variable-sized cavitations containing liquefied caseum in carnivores' lungs. The lungs, livers, and spleens of non-human primates exhibited small to medium-sized nodules. Histologically, lesions were divided into four categories (Types I, II, III, and IV) based on the extent of necrosis, the presence of mineralization, giant cells, and fibrous encapsulation. Extensive caseous necrosis with calcification, abundant giant cells, and thick fibroblastic encapsulation were consistent findings in the lungs, livers, and lymph nodes of bovids and cervids, whereas airway impaction with cellular exudate containing a teeming number of acid-fast bacilli and, at times, alveolar rupture leading to cavity formation was present in the lungs of carnivores. Absence of calcification and fibrous encapsulation was recorded in lungs of non-human primates. Immunohistochemical labelling with anti-early secretory antigenic target-6 (ESAT-6) and culture filtrate protein-10 (CFP-10) antibodies showed mild, moderate, and intense positive reactions in type II and III, type I, and type IV granulomatous lesions, respectively. Molecular detection by PCR revealed Mycobacterium tuberculosis (12 carnivores, 02 non-human primates and 01 pachyderm), M. bovis (02 cervids and 01 bovid) and M. orygis (02 cervids and 01 bovid). Cultural isolation confirmed M. tuberculosis in 03 carnivores and M. orygis in 02 cervids and 01 bovid. Our findings imply that TB is quite prevalent in the wildlife of India and there are considerable differences in the histomorphological lesions induced by distinct Mycobacterium species in different wild animals. The circulation of TB organisms in wild animals warrants a strict surveillance programme to identify the carrier status of these animals so that effective TB control strategies can be formulated to prevent spillover and spillback incidences at the human-livestock-wildlife interface.

Local assessment of the immunohistochemical expression of Foxp3+ regulatory T lymphocytes in the different pathological forms associated with bovine paratuberculosis.

BACKGROUND: Mycobacterium avium subsp. paratuberculosis infected animals show a variety of granulomatous lesions, from focal forms with well-demarcated granulomas restricted to the gut-associated lymphoid tissue (GALT), that are seen in the initial phases or latency stages, to a diffuse granulomatous enteritis, with abundant (multibacillary) or scant (paucibacillary) bacteria, seen in clinical stages. Factors that determine the response to the infection, responsible for the occurrence of the different types of lesion, are still not fully determined. It has been seen that regulatory T cells (Treg) play an important role in various diseases where they act on the limitation of the immunopathology associated with the immune response. In the case of paratuberculosis (PTB) the role of Treg lymphocytes in the immunity against Map is far away to be completely understood; therefore, several studies addressing this subject have appeared recently. The aim of this work was to assess, by immunohistochemical methods, the presence of Foxp3+ T lymphocytes in intestinal samples with different types of lesions seen in cows with PTB. METHODS: Intestinal samples of twenty cows showing the different pathological forms of PTB were evaluated: uninfected controls (n = 5), focal lesions (n = 5), diffuse paucibacillary (n = 5) and diffuse multibacillary (n = 5) forms. Foxp3+ lymphocyte distribution was assessed by differential cell count in intestinal lamina propria (LP), gut-associated lymphoid tissue (GALT) and mesenteric lymph node (MLN). RESULTS: A significant increase in the number of Foxp3+ T cells was observed in infected animals with respect to control group, regardless of the type of lesion. However, when the different categories of lesion were analyzed independently, all individuals with PTB lesions showed an increase in the amount of Foxp3+ T lymphocytes compared to the control group but this increase was only significant in cows with focal lesions and, to a lesser extent, in animals with diffuse paucibacillary forms. The former showed the highest numbers, significantly different from those found in cows with diffuse lesions, where no differences were noted between the two forms. No specific distribution pattern was observed within the granulomatous lesions in any of the groups. CONCLUSIONS: The increase of Foxp3+ T cells in focal forms, that have been associated with latency or resistance to infection, suggest an anti-inflammatory action of these cells at these stages, helping to prevent exacerbation of the inflammatory response, as occurs in diffuse forms, responsible for the appearance of clinical signs.

Canine Leproid Granuloma (CLG) Caused by Mycobacterial Species Closely Related to Members of Mycobacterium Simiae Complex in a Dog in Brazil.

This report describes the clinical features and molecular diagnosis of a case of canine leproid granuloma (CLG) caused by mycobacterial strains of the Mycobacterium simiae complex in Brazil. A 12-year-old non-neutered male Labrador Retriever dog was presented with a 2-week history of progressive painless cutaneous lesions. Ulcerated nodules with hematic crusts were observed on the dorsal surface of the right and left pinna and on the metacarpal, metatarsal, and digits. Complete blood count, serum biochemistry, aspiration cytology of cutaneous lesions, biopsy for histopathological evaluation, culture for aerobic and anaerobic bacteria, polymerase chain reaction and DNA sequencing to identify mycobacterial species were performed. According to the clinical and histopathological findings, a diagnosis of CLG was established. Despite the negative result of the bacterial culture, mycobacterial identification was made by sequencing the hsp65 gene. Our findings highlight that mycobacterial species closely related to members of the M simiae clade can be causative agents of CLG.

WhiB4 Is Required for the Reactivation of Persistent Infection of Mycobacterium marinum in Zebrafish.

Granulomas are the pathological hallmark of tuberculosis (TB). In individuals with latent TB infection, Mycobacterium tuberculosis cells reside within granulomas in a nonreplicating dormant state, and a portion of them will develop active TB. Little is known on the bacterial mechanisms/factors involved in this process. In this study, we found that WhiB4, an oxygen sensor and a transcription factor, plays a critical role in disease progression and reactivation of Mycobacterium marinum (M. marinum) infection in zebrafish. We show that the whiB4::Tn mutant of M. marinum caused persistent infection in adult zebrafish, which is characterized by the lower but stable bacterial loads, constant number of nonnecrotized granulomas in fewer organs, and reduced inflammation compared to those of zebrafish infected with the wild-type bacteria or the complemented strain. The mutant bacteria in zebrafish were also less responsive to antibiotic treatments. Moreover, the whiB4::Tn mutant was defective in resuscitation from hypoxia-induced dormancy and the DosR regulon was dysregulated in the mutant. Taken together, our results suggest that WhiB4 is a major driver of reactivation from persistent infection. IMPORTANCE About one-quarter of the world's population has latent TB infection, and 5 to 10% of those individuals will fall ill with TB. Our finding suggests that WhiB4 is an attractive target for the development of novel therapeutics, which may help to prevent the reactivation of latent infection, thereby reducing the incidences of active TB.

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.

Immunological aspects of host-pathogen crosstalk in the co-pathogenesis of diabetes and latent tuberculosis.

Introduction: Diabetes is a potent risk factor for the activation of latent tuberculosis and worsens the tuberculosis (TB) treatment outcome. The major reason for mortality and morbidity in diabetic patients is due to their increased susceptibility to TB. Thus, the study was conducted to understand the crosstalk between M. tuberculosis and its host upon latent tuberculosis infection and under hyperglycemic conditions or diabetes. Methods: An animal model was employed to study the relationship between latent tuberculosis and diabetes. BCG immunization was done in mice before infection with M. tuberculosis, and latency was confirmed by bacillary load, histopathological changes in the lungs and gene expression of hspX, tgs1, tgs3 and tgs5. Diabetes was then induced by a single high dose of streptozotocin (150 mg/kg body weight). Host factors, like various cytokines and MMPs (Matrix metalloproteinases), which play an important role in the containment of mycobacterial infection were studied in vivo and in vitro. Results: A murine model of latent TB was developed, which was confirmed by CFU counts (<104 in the lungs and spleen) and granuloma formation in lungs in the latent TB group. Also, the gene expression of hspX, tgs1, and tgs5 was upregulated, and after diabetes induction, blood glucose levels were >200 mg/dl. An in vitro study employing a THP-1 macrophage model of latent and active tuberculosis under normal and high glucose conditions showed that dormant bacilli were better contained in the presence of 5.5 mM glucose concentration as compared with active bacilli. However, the killing and restriction efficiency of macrophages decreased, and CFU counts increased significantly with an increase in glucose concentration. Discussion: The decreased levels of MCP-1, decreased expression of mmp-9, and increased expression of mmp-1 in the latent group at high glucose concentrations could explain the failure of granuloma formation at high glucose conditions.

Interleukin-13-Overexpressing Mice Represent an Advanced Preclinical Model for Detecting the Distribution of Antimycobacterial Drugs within Centrally Necrotizing Granulomas.

The Mycobacterium tuberculosis-harboring granuloma with a necrotic center surrounded by a fibrous capsule is the hallmark of tuberculosis (TB). For a successful treatment, antibiotics need to penetrate these complex structures to reach their bacterial targets. Hence, animal models reflecting the pulmonary pathology of TB patients are of particular importance to improve the preclinical validation of novel drug candidates. M. tuberculosis-infected interleukin-13-overexpressing (IL-13tg) mice develop a TB pathology very similar to patients and, in contrast to other mouse models, also share pathogenetic mechanisms. Accordingly, IL-13tg animals represent an ideal model for analyzing the penetration of novel anti-TB drugs into various compartments of necrotic granulomas by matrix-assisted laser desorption/ionization-mass spectrometry imaging (MALDI-MS imaging). In the present study, we evaluated the suitability of BALB/c IL-13tg mice for determining the antibiotic distribution within necrotizing lesions. To this end, we established a workflow based on the inactivation of M. tuberculosis by gamma irradiation while preserving lung tissue integrity and drug distribution, which is essential for correlating drug penetration with lesion pathology. MALDI-MS imaging analysis of clofazimine, pyrazinamide, and rifampicin revealed a drug-specific distribution within different lesion types, including cellular granulomas, developing in BALB/c wild-type mice, and necrotic granulomas in BALB/c IL-13tg animals, emphasizing the necessity of preclinical models reflecting human pathology. Most importantly, our study demonstrates that BALB/c IL-13tg mice recapitulate the penetration of antibiotics into human lesions. Therefore, our workflow in combination with the IL-13tg mouse model provides an improved and accelerated evaluation of novel anti-TB drugs and new regimens in the preclinical stage.