Non-tuberculous mycobacterial skin and soft tissue infections in the Northern Territory, Australia, 1989-2021

The gut-lung axis and microbiome dysbiosis in non-tuberculous mycobacterial infections: immune mechanisms, clinical implications, and therapeutic frontiers

Non-tuberculous mycobacteria (NTM) are emerging pathogens of global concern, particularly in regions with declining tuberculosis rates. This review synthesizes current evidence on the epidemiology, immune pathogenesis, and microbiome interactions underlying NTM infections. The rising incidence of NTM is driven by environmental factors, immunocompromised populations, and advanced diagnostics. Clinically, NTM manifests as pulmonary, lymphatic, skin/soft tissue, or disseminated disease, with Mycobacterium avium complex (MAC) and M. abscessus being predominant pathogens. Host immunity, particularly Th1 responses mediated by IL-12/IFN-γ and TLR2 signaling, is critical for controlling NTM, while dysregulated immunity (e.g., elevated Th2 cytokines, PD-1/IL-10 pathways) exacerbates susceptibility. Emerging research highlights the gut-lung axis as a pivotal mediator of disease, where microbiome dysbiosis-marked by reduced Prevotella and Bifidobacterium-impairs systemic immunity and promotes NTM progression. Short-chain fatty acids (SCFAs) and microbial metabolites like inosine modulate macrophage and T-cell responses, offering therapeutic potential. Studies reveal distinct airway microbiome signatures in NTM patients, characterized by enriched Streptococcus and Prevotella, and reduced diversity linked to worse outcomes. Despite advances, treatment remains challenging due to biofilm formation, antibiotic resistance, and relapse rates. This review underscores the need for microbiome-targeted therapies, personalized medicine, and longitudinal studies to unravel causal relationships between microbial ecology and NTM pathogenesis.

Targeting Autophagy as a Strategy for Developing New Host-Directed Therapeutics Against Nontuberculous Mycobacteria

Nontuberculous mycobacteria (NTMs) are increasingly being recognized as opportunistic pathogens in clinical practice because of their innate resistance to antimicrobial treatment and the widespread increase in multidrug-resistant strains on a global scale. NTMs pose a tremendous infection management challenge, especially in individuals with pre-existing lung conditions, as well as those who are immunocompromised. NTMs' capability to evade or suppress the immune responses of their host is a key feature that makes them a cause of persistent chronic infection. Autophagy, an essential cellular defense mechanism that delivers and breaks down intracellular materials in lysosomes, protects the host from mycobacterial infection. Initial studies have revealed encouraging therapeutic strategies that augment endogenous autophagic mechanisms or block harmful host responses, thus having the potential to decrease intracellular mycobacterial infection, including that caused by multidrug-resistant strains. This review discusses how NTMs can evade autophagic mechanisms and considers the possibilities of using autophagy-inducing agents to develop novel therapeutic strategies to combat NTM infection.

Nontuberculosis Mycobacterium Infections in Orthopaedic Surgery: Review of the Epidemiology, Pathogenesis, Diagnosis, and Treatment Guidelines

Nontuberculosis Mycobacterium infections are rare but devastating infections in orthopaedic surgery. The complexity of treatment and the high rate of treatment failure for nontuberculosis Mycobacterium infections illustrate their unique pathogenesis and success at evading normal immune responses. To date, there is no formal treatment algorithm developed for managing these infections in orthopaedic surgery. Successful eradication relies on prolonged culture-specific antibiotic therapies coupled with surgical resection, implant/prosthesis removal, and occasionally amputations. These multidrug therapies often have a high rate of complications, drug-drug interactions, and poor tolerance, further increasing the complexity of treatment. Outlining the epidemiology, pathogenesis, diagnosis, and treatment guidelines of these rare but detrimental infections is essential to improving treatment success.

Clinical presentation and treatment outcomes of extrapulmonary nontuberculous mycobacterial infections with rapid and slow growth rates in Cali, Colombia

INTRODUCTION

The increasing prevalence of extrapulmonary nontuberculous mycobacterial (NTM) infections poses significant challenges in clinical management due to their inherent drug resistance, the need for prolonged antibiotic regimens and the complexities associated with surgical management. Although these infections are infrequent in daily clinical practice, detailed information on associated clinical outcomes is lacking in the local literature.

MATERIALS AND METHODS

This descriptive observational study examined 17 patients with extrapulmonary NTM infection from the General Mycobacteria Registry of Fundación Valle del Lili University Hospital (FVL), a leading reference care center located in Cali, a city in southwestern Colombia. Notably, Cali is classified as a high-risk area for tuberculosis. The study reviewed a total of 391 patients between 2007 and 2021.

RESULTS

A predominance of women with a history of cosmetic surgery was observed, with the skin being the most common site of involvement, especially for M. fortuitum complex and M. abscessus complex. Clarithromycin based therapy was given to 14/18 (82.3%) of the patients. The mean duration of treatment was 4-6 months, for a cure rate of 15/17 (88.2%).

CONCLUSION

The treatment regimens implemented mostly align with the literature recommendations. However, it is essential to note that while the observed cure rate exceeds 80%, this assertion is tempered by the limitation imposed by the lack of confirmatory imaging in some cases. A contributing factor to the higher cure rate observed in this study may be the use of more extensive surgical interventions, with some patients undergoing more than one procedure. Given the limited number of case series on extrapulmonary nontuberculous mycobacterial infections, these findings emphasize the potential importance of surgical management in achieving higher cure rates. The observed cure rate suggests potentially better clinical management of these infections in our region and underscores the need for future research to understand the factors contributing to this comparative therapeutic success.

Application of surgical management combined with photodynamic therapy in the treatment of nontuberculous mycobacterial infections after cosmetic surgery

BACKGROUND

In recent years, the number of patients with nontuberculous mycobacteria (NTM) infections caused by invasive procedures such as cosmetic surgery has been increasing. However, treating NTM infections presents significant challenges, with no standardized diagnostic or treatment guidelines currently available.

METHODS

This study included 10 patients diagnosed with skin and soft tissue NTM infections following cosmetic surgery. Each patient underwent surgical treatment, followed by Photodynamic therapy (PDT) after debridement. PDT was performed using topical 20 % 5-aminolevulinic acid (ALA, 2 mL: 10 mg) applied to the wound periphery (2 cm margin), followed by a 3-hour incubation under light occlusion and activation with a 635 nm diode laser at an energy density of 120 J/cm². Exposure durations were dynamically adjusted (20-40 min) based on real-time pain tolerance. Weekly PDT sessions were administered, with total treatment duration individualized according to wound healing progression. Post-procedural pain was assessed using the Facial Expression Pain Scale (FEPS) and managed through a tiered protocol: ice compression for mild-to-moderate pain (FEPS 2-4) and NSAIDs/opioids for severe pain (FEPS >4). Antibiotics were selected based on the results of drug susceptibility testing.

RESULTS

All ten patients achieved clinical cure, with a notable reduction in the duration of therapy. All patients were followed for over six months without recurrence of infection. Post-PDT pain was universally in all patients, with FEPS scores ranging from 2 to 7, and managed effectively by the final treatment. Transient adverse events included erythema (n = 10) and pruritus (n = 2), resolving spontaneously within 48 h. No chronic complications were observed.

CONCLUSION

The combination of surgical intervention and PDT, along with appropriate antibiotic therapy, may be a safe and effective approach for treating skin and soft tissue NTM infections after cosmetic surgery.

Epidemiology and clinical outcomes in skin and soft tissue nontuberculous mycobacteria infections: A retrospective study

BACKGROUND

Nontuberculous mycobacteria (NTM) are emerging pathogens responsible for increasing skin and soft tissue infections (SSTIs) globally. However, the diagnosis and treatment of NTM SSTIs face significant challenges due to the lack of standardized guidelines. This study reviewed the clinical characteristics, diagnostic challenges, and treatment outcomes of NTM SSTIs in a large cohort from a tertiary referral center in Beijing, China.

METHODS

We retrospectively reviewed 142 patients diagnosed with NTM SSTIs at a tertiary hospital from 2014 to 2023. Data collected included clinical presentation, microbiologic and histopathologic findings, diagnostic methods, treatment regimens, and outcomes. The patients were categorized based on NTM species, and immunocompromised status.

RESULTS

The cohort included patients with various NTM species, with M. marinum, M. avium complex (MAC), and M. abscessus complex (MABC) being the most common. The number of patients with NTM infections increased annually (p < 0.01). Fifty-four patients (38.0 %) were immunocompromised. The likelihood of immunosuppression was significantly higher in the MAC group (90.0 %, p = 0.02) and M. kansasii group (80.0 %). The highest proportion of sporotrichosis-pattern lesions was observed in M. marinum infections (p = 0.03). MAC primarily caused extracutaneous disseminated infections (p = 0.05), and immunosuppressed patients were more likely to have extracutaneous infections (79.6 %, p = 0.01). Of the 41 disseminated infection cases, 17.1 % had prior pulmonary NTM infections later disseminated to the skin and had a significantly worse prognosis (p < 0.01). Most misdiagnosed cases (82.6 %) were initially considered skin tuberculosis and bacterial infections. Amikacin was the most consistently effective antibiotic, while resistance to cefoxitin and imipenem was common in MABC and M. chelonae. The MABC strains exhibited 40 % resistance to clarithromycin. Drug side effects occurred in 30.3 % of patients, with 8.5 % switching medications due to adverse impacts. The longest treatment duration was in M. kansasii cases (371.4 days, p = 0.03). Immunosuppressed patients received more drugs (Mean ± SD: 3.0 ± 0.9 vs 2.8 ± 0.7, p = 0.02), whereas showed a nonsignificant trend toward longer treatment durations.

CONCLUSIONS

The study highlighted significant challenges in differentiating NTM infections from other conditions and managing their diverse clinical manifestations. Enhanced diagnostic tools and standardized treatment guidelines are essential to improve patient outcomes and manage the increasing burden of NTM SSTIs.

Management of Mycobacterium ulcerans infection (Buruli ulcer) in Australia: consensus statement

INTRODUCTION

Buruli ulcer, caused by Mycobacterium ulcerans, is increasing in incidence and spreading to new areas in southeast Australia. With increasing experience and emerging evidence, this consensus statement considers contemporary data to provide up-to-date recommendations to clinicians who may encounter this disease. The emergence of Buruli ulcer in previously non-endemic areas highlights the importance of increasing clinician and community awareness of this disease. Main recommendations and changes in management as a result of this consensus statement: Buruli ulcer is a notifiable disease in Victoria, the Northern Territory and Queensland. Cases identified in other states or territories should be discussed with relevant health authorities. We call for Buruli ulcer to be made nationally notifiable to monitor for its potential emergence in non-endemic regions. Diagnosis using polymerase chain reaction is sensitive and specific if performed correctly; a dry swab under the undermined edge of ulcers or a tissue sample via punch biopsy if the lesion is not ulcerated is recommended. If swabs are incorrectly performed or performed on non-ulcerated skin, they can give a false negative result. There is high quality evidence to support treatment of eight weeks' duration using rifampicin-based dual oral antibiotic therapy, in combination with clarithromycin or a fluoroquinolone; relapse is very rare but can occur in people with risk factors. There is emerging evidence for shorter durations of treatment (six weeks) in individuals with small lesions who are at low risk of relapse and in those who have undergone surgical excision of the lesion (four weeks). Patients should be warned that ulcers typically enlarge with antibiotic treatment, will not have healed by completion of antibiotics, and take a median of four to five months to heal. Surgical management is usually not required, but may be beneficial to reduce healing times, avoid or reduce the duration of antibiotics, and manage paradoxical reactions. Early identification and treatment of paradoxical reactions is important, as they are associated with increased tissue necrosis and delayed wound healing. Good wound care is critical in successful treatment of Buruli ulcer, as it enhances healing and prevents secondary bacterial infection. Compared with adults, children have a higher proportion of non-ulcerative and severe lesions, are less likely to experience adverse antibiotic effects, but have higher rates of paradoxical reactions; specialist referral is recommended.

Mycobacterium fortuitum : A Rare Cause of Surgical Site Infection

Mycobacterium fortuitum is a rapidly growing nontuberculous mycobacterium mainly associated with skin, soft tissue and surgical site infections. We report an unusual outbreak of 6 cases of surgical site infection following spinal surgery. Patients received combined intravenous antibiotics, including amikacin, followed by an extended period of oral therapy with favorable clinical outcomes. No instrumentation replacement was performed in any case.

Mycobacterium heraklionense: An emerging cause of hand tenosynovitis

Misdiagnosis of Mycobacterium heraklionense tenosynovitis is common due to the challenging identification and perceived rarity of the disease. This can result in delayed therapy initiation and potentially irreversible consequences. In this report, we present an additional case of hand tenosynovitis, which highlights the diagnostic and management challenges of Mycobacterium heraklionense tenosynovitis and provides further evidence of its emergence as a cause of tenosynovitis. Additionally, we provide a comprehensive summary of published case reports that describe Mycobacterium heraklionense tenosynovitis.

High-resolution 2D solid-state NMR provides insights into nontuberculous mycobacteria

We present a high-resolution magic-angle spinning (MAS) solid-state NMR (ssNMR) study to characterize nontuberculous mycobacteria (NTM). We studied two different NTM strains, Mycobacterium smegmatis, a model, non-pathogenic strain, and Mycobacterium abscessus, an emerging and important human pathogen. Hydrated NTM samples were studied at natural abundance without isotope-labelling, as whole-cells versus cell envelope isolates, and native versus fixed sample preparations. We utilized 1D13C and 2D 1H-13C ssNMR spectra and peak deconvolution to identify NTM cell-wall chemical sites. More than ∼100 distinct 13C signals were identified in the ssNMR spectra. We provide tentative assignments for ∼30 polysaccharides by using well resolved 1H/13C chemical shifts from the 2D INEPT-based 1H-13C ssNMR spectrum. The signals originating from both the flexible and rigid fractions of the whole-cell bacteria samples were selectively analyzed by utilizing either CP or INEPT based 13C ssNMR spectra. CP buildup curves provide insights into the dynamical similarity of the cell-wall components for NTM strains. Signals from peptidoglycan, arabinogalactan and mycolic acid were identified. The majority of the 13C signals were not affected by fixation of the whole cell samples. The isolated cell envelope NMR spectrum overlap with the whole-cell spectrum to a large extent, where the latter has more signals. As an orthogonal way of characterizing these bacteria, electron microscopy (EM) was used to provide spatial information. ssNMR and EM data suggest that the M. abscessus cell-wall is composed of a smaller peptidoglycan layer which is more flexible compared to M. smegmatis, which may be related to its higher pathogenicity. Here in this work, we used high-resolution 2D ssNMR first time to characterize NTM strains and identify chemical sites. These results will aid the development of structure-based approaches to combat NTM infections.

Metagenomic next-generation sequencing may assist diagnosis of osteomyelitis caused by Mycobacterium houstonense: A case report

BACKGROUND

Mycobacterium houstonense (M. houstonense) belongs to the nontuberculous mycobacterium group. Infection caused by M. houstonense is prone to recurrence.

CASE SUMMARY

We present a patient who was diagnosed with osteomyelitis caused by M. houstonense and treated with a combination of cefoxitin, and amikacin combined with linezolid.

CONCLUSION

The emergence of metagenomic next-generation sequencing (NGS) has brought new hope for the diagnosis and treatment of listeria meningitis. NGS can analyze a large number of nucleic acid sequences in a short time and quickly determine the pathogen species in the sample. Compared with traditional cerebrospinal fluid culture, NGS can greatly shorten the diagnosis time and provide strong support for the timely treatment of patients. Regarding treatment, NGS can also play an important role. Rapid and accurate diagnosis can enable patients to start targeted treatment as soon as possible and improve the treatment effect. At the same time, by monitoring the changes in pathogen resistance, the treatment plan can be adjusted in time to avoid treatment failure.

Primary cutaneous infections with non-tuberculous mycobacteria: a report of 6 cases

BACKGROUND

The incidence of non-tuberculous mycobacterium infection has shown a gradual increasing trend in recent years, among which cutaneous manifestations as an important aspect. This study aimed to describe the clinical features and microbiological findings in 6 cases of primary cutaneous nontuberculous mycobacterium infection.

METHODS

In this retrospective study from June 2021 to June 2022, the clinical data and microbiological results of six cases diagnosed with primary cutaneous non-tuberculous mycobacterium infection in department of dermatology, Hangzhou Third People's Hospital were analyzed.

RESULTS

All six cases were primary cutaneous non-tuberculous mycobacterium infections, four of which had a history of trauma or exposure, and two had an underlying disease that could lead to compromised immunity. All patients presented with erythema nodular skin lesions, four on the upper or lower extremities, one on the face, and one on the right hip. The histopathological findings of five patients who underwent biopsy were granulomatous inflammatory changes with mixed infiltration. Laboratory cultures using tissue or tissue fluid were all successful, including four Mycobacterium marinum, one Mycobacterium abscessus, and one Mycobacterium avium. Metagenomics next-generation sequencing detected results consistent with culture colonies in only two cases. With the exception of case 4, all patients responded well to oral medication, with a course of treatment ranging from 4 months to 1 year, and the prognosis was good.

CONCLUSIONS

The clinical features of primary cutaneous non-tuberculous mycobacterium infection are often lacking in specificity, and the identification of related strains is difficult for a variety of reasons. Although the results of metagenomics next-generation sequencing are useful for pathogen spectrum identification, its diagnostic value should be carefully reevaluated under certain circumstances. Patients with suspected triggers who do not respond well to conventional treatments should be suspected as atypical infection and potential immunosuppression. If diagnosed and treated promptly, the prognosis of primary cutaneous non-tuberculous mycobacterium infection is generally good.

Buruli ulcer surveillance in south-eastern Australian possums: Infection status, lesion mapping and internal distribution of Mycobacterium ulcerans

Buruli ulcer (BU) is a neglected tropical disease of skin and subcutaneous tissues caused by Mycobacterium ulcerans. BU-endemic areas are highly focal, and M. ulcerans transmission dynamics vary by setting. In Victoria, Australia, BU is an endemic vector-borne zoonosis, with mosquitoes and native possums implicated in transmission, and humans incidental hosts. Despite the importance of possums as wildlife reservoirs of M. ulcerans, knowledge of BU in these animals is limited. Opportunistic necropsy-based and active trap-and-release surveillance studies were conducted across Melbourne and Geelong, Victoria, to investigate BU in possums. Demographic data and biological samples were collected, and cutaneous lesions suggestive of BU were mapped. Samples were tested for the presence of M. ulcerans DNA by IS2404 qPCR. The final dataset included 26 possums: 20 necropsied; 6 trapped and released. Most possums (77%) were common ringtails from inner Melbourne. Nine had ulcers, ranging from single and mild, to multiple and severe, exposing bones and tendons in three cases. M. ulcerans was confirmed in 73% (19/26) of examined possums: 8 with lesions and 11 without. Oral swabs were most frequently indicative of M. ulcerans infection status. Severely ulcerated possums had widespread systemic internal bacterial dissemination and were shedding M. ulcerans in faeces. The anatomical distribution of ulcers and PCR positivity of biological samples suggests possums may contract BU from bites of M. ulcerans-harbouring mosquitoes, traumatic skin wounds, ingestion of an unknown environmental source, and/or during early development in the pouch. Ringtail possums appear highly susceptible to infection with M. ulcerans and are important bacterial reservoirs in Victoria. Oral swabs should be considered for diagnosis or surveillance of infected possums. A One Health approach is needed to design and implement integrated interventions that reduce M. ulcerans transmission in Victoria, thereby protecting wildlife and humans from this emerging zoonotic disease.

Mortality Rate and Cause of Death in Adults with Extrapulmonary Nontuberculous Mycobacteria Infection, Denmark

Evidence on mortality rates and causes of death associated with extrapulmonary nontuberculous mycobacteria (NTM) infection is limited. This nationwide register-based study in Denmark used diagnostic codes to match adult patients with extrapulmonary NTM infection 1:4 to controls. During 2000–2017, we identified 485 patients, who had significantly more comorbidities than controls. The 5-year mortality rate for patients was 26.8% (95% CI 23.1%–31.0%) and for controls, 10.9% (95% CI 9.6%–12.4%). The median age at death was 76 (interquartile range 63–85) years for patients and 84 (interquartile range 73–90) years for controls. The adjusted hazard rate of death for patients was 1.34 (95% CI 1.10–1.63; p = 0.004). Patients and controls mainly died of cardiovascular disease and solid malignant neoplasms. Hematologic malignancies and HIV were more frequently causes of death in patients. Mortality rates are substantial among patients with extrapulmonary NTM infection, predominantly caused by underlying conditions.

Nationwide Increasing Incidence of Nontuberculous Mycobacterial Diseases Among Adults in Denmark: Eighteen Years of Follow-Up

BACKGROUND

The epidemiology of nontuberculous mycobacteria (NTM) infections is not well described. In this study, we sought to determine the incidence and prevalence of NTM infections and focus on social risk factors. In addition, we describe people with pulmonary and extrapulmonary NTM.

RESEARCH QUESTION

What are the incidence and prevalence of NTM in Denmark, and what are the characteristics of the affected patients?

STUDY DESIGN AND METHODS

This is a nationwide retrospective register-based cohort study in Denmark. Adult patients in the Danish national registers who received a diagnosis of NTM disease from 2000 to 2017 were classified as having either pulmonary or extrapulmonary NTM disease.

RESULTS

We identified 1,146 adults with an NTM diagnosis. Of these, 661 patients had pulmonary NTM, of whom 50.4% were male, whereas 485 had extrapulmonary NTM, of whom 59.6% were male. The median age (interquartile range) was 66 (18) years and 57 (32) years, respectively. The yearly incidence rate per 100,000 increased between 2000 and 2017 for both pulmonary NTM (0.4 to 1.3) and extrapulmonary NTM (0.3 to 0.6). The annual prevalence per 100,000 inhabitants increased from 0.4 to 3.5 for pulmonary NTM and from 0.3 to 1.0 for extrapulmonary NTM. The incidence rate increased with age. The incidence of pulmonary NTM was highest among those who were aged 70 years or older (19.3 per 100,000 inhabitants). Compared with patients with pulmonary NTM, patients with extrapulmonary NTM were more likely to be employed and had a higher educational level.

INTERPRETATION

This study indicates that the prevalence of NTM disease in Denmark increased between 2000 and 2017. We found that patients with pulmonary NTM and patients with extrapulmonary NTM represent two distinct groups that differ in age, sex, education, and employment status. Increased suspicion of pulmonary NTM disease is warranted in older adults after exclusion of more common lung infections.