"Mycobacterium tilburgii," a newly described, uncultivated opportunistic pathogen

Epidemiology, diagnosis & treatment of non-tuberculous mycobacterial diseases

Non-tuberculous mycobacteria (NTM) are ubiquitously present in the environment, but NTM diseases occur infrequently. NTM are generally considered to be less virulent than Mycobacterium tuberculosis, however, these organisms can cause diseases in both immunocompromised and immunocompetent hosts. As compared to tuberculosis, person-to-person transmission does not occur except with M. abscessus NTM species among cystic fibrosis patients. Lung is the most commonly involved organ, and the NTM-pulmonary disease (NTM-PD) occurs frequently in patients with pre-existing lung disease. NTM may also present as localized disease involving extrapulmonary sites such as lymph nodes, skin and soft tissues and rarely bones. Disseminated NTM disease is rare and occurs in individuals with congenital or acquired immune defects such as HIV/AIDS. Rapid molecular tests are now available for confirmation of NTM diagnosis at species and subspecies level. Drug susceptibility testing (DST) is not routinely done except in non-responsive disease due to slowly growing mycobacteria ( M. avium complex, M. kansasii) or infection due to rapidly growing mycobacteria, especially M. abscessus. While the decision to treat the patients with NTM-PD is made carefully, the treatment is given for 12 months after sputum culture conversion. Additional measures include pulmonary rehabilitation and correction of malnutrition. Treatment response in NTM-PD is variable and depends on isolated NTM species and severity of the underlying PD. Surgery is reserved for patients with localized disease with good pulmonary functions. Future research should focus on the development and validation of non-culture-based rapid diagnostic tests for early diagnosis and discovery of newer drugs with greater efficacy and lesser toxicity than the available ones.

Feline leprosy due to Candidatus 'Mycobacterium lepraefelis': Further clinical and molecular characterisation of eight previously reported cases and an additional 30 cases

OBJECTIVES

This paper, the last in a series of three on 'feline leprosy', provides a detailed description of disease referable to the previously unnamed species, Candidatus 'Mycobacterium lepraefelis', a close relative of the human pathogens Mycobacterium leprae and Mycobacterium lepromatosis.

METHODS

Cases were sourced retrospectively and prospectively for this observational study, describing clinical, geographical and molecular microbiological data for cats definitively diagnosed with Candidatus 'M lepraefelis' infection.

RESULTS

A total of 145 cases of feline leprosy were scrutinised; 114 'new' cases were sourced from the Victorian Infectious Diseases Reference Laboratory (VIDRL) records, veterinary pathology laboratories or veterinarians, and 31 cases were derived from six published studies. Thirty-eight cats were definitively diagnosed with Candidatus 'M lepraefelis' infection. Typically, cats tended to be middle-aged or older when first infected, with a male predilection. Affected cats typically had widespread cutaneous lesions, in some cases after initially localised disease. Advanced cases were often systemically unwell. All cats had outdoor access. The histological picture was lepromatous in the majority of patients, although two cases had tuberculoid disease. In one case that underwent necropsy, lesions were evident in the liver, spleen and lungs. Treatment was varied, although most cats received a combination of oral clarithromycin and rifampicin. Prognosis for recovery was variable, but typically poor.

CONCLUSIONS AND RELEVANCE

Candidatus 'M lepraefelis' typically causes high bacterial index (lepromatous) feline leprosy that in some cases progresses to systemic mycobacteriosis. The disease has a variable clinical course and prognosis. Many cases either died or were euthanased due to the infection. Multilocus sequence analysis reveals a heterogeneous picture and further analysis of draft genome sequencing may give clues to the taxonomy and epidemiology of this organism. Prospective treatment trials and/or additional drug susceptibility testing in specialised systems would further inform treatment recommendations. Comparative aspects: This paper finishes with a discussion of comparative aspects of infection caused by the three feline leproid disease agents that have been the subject of this series: Candidatus 'Mycobacterium tarwinense', Mycobacterium lepraemurium and Candidatus 'M lepraefelis'.

Case report of fatal Mycobacterium tilburgii infection

There are few reports concerning Mycobacterium tilburgii infection in humans because this bacterium is non-cultivatable. Herein, using new molecular techniques, we report the case of an immunocompromised patient with fatal disseminated lymphadenitis that was caused by M. tilburgii.26 years old Caucasian HIV negative female patient presented with abdominal pain. Her clinical assessment revealed disseminated lymphadenitis, that was acid fast bacilli positive. Further molecular evaluation showed the causative agent as M. tilburgii. Despite anti mycobacterial therapy and careful management of intervening complications patient died because of an intraabdominal sepsis. This is the first fatal M. tilburgii infection in the literature. This case points the importance of careful management of patient's immune status and intervening infections besides implementation of effective drug treatment.

Disseminated infection with Mycobacterium tilburgii in a male immunocompromised patient

Mycobacterium tilburgii is a nonculturable nontuberculous mycobacterium identifiable only by molecular methods. We report a case of disseminated M. tilburgii infection illustrating the importance of 16S rRNA gene sequencing to determine the responsible mycobacterial pathogen and the difficulties in tailoring antimycobacterial treatment in the absence of a culturable organism.

IL-12Rβ1 deficiency and disseminated Mycobacterium tilburgii disease

Mycobacterium tilburgii rarely causes disseminated disease. We describe a case of M. tilburgii infection in an otherwise healthy 33-year-old woman, who was found to carry bi-allelic mutations of the gene encoding the β1 chain of the IL-12 receptor.

"Mycobacterium tilburgii" infection in two immunocompromised children: importance of molecular tools in culture-negative mycobacterial disease diagnosis

"Mycobacterium tilburgii" is a nontuberculous mycobacterium that cannot be cultured by current techniques. It is described as causing disseminated disease in adults. We present the first cases of disseminated disease in 2 immunocompromised children. This paper stresses the importance of molecular techniques for correct mycobacterial identification and guidance to immunological diagnosis.