MIIM30011 2024 L32 - Non-TB Mycos (PDF)

Non-tuberculous mycobacteria Lecture 32 Dr Sacha Pidot [email protected] www.pidotlab.com  By the end of this lecture you should be able to: To understand key features of organisms in the genus Mycobacterium Identify the major virulence factors...

Non-tuberculous mycobacteria Lecture 32 Dr Sacha Pidot [email protected] www.pidotlab.com  By the end of this lecture you should be able to: To understand key features of organisms in the genus Mycobacterium Identify the major virulence factors of Mycobacterium tuberculosis To understand key features of major non- tuberculosis pathogens and compounds used to treat mycobacterial infections  The genus Mycobacterium Member of the Actinobacteria – 190 species within genus Mycobacterium – Includes major human pathogens Mycobacterium tuberculosis Mycobacterium leprae Non-tuberculous mycobacteria (NTM) O’Neill et al, 2015, PLoS Pathogens, Core genome tree  Mycobacterium leprae Causative agent of Leprosy (Hansen’s disease) – Chronic infectious disease of nerves, skin, eyes and nasal mucosa – Infection of nerves → loss of sensation → can lead to injuries or paralysis of hands/feet – Symptoms can take 20 years to emerge Transmission not completely defined – Believed to be spread by coughing or contact with nasal secretions from infected individual – Requires close, prolonged contact over months – Overall, low infection risk  M. leprae epidemiology >200,000 cases per year in >100 countries – >4mil people living with leprosy-related impairment – 80% of all new cases in India, Indonesia and Brazil – Armadillos, squirrels and non-human primates are reservoirs  M. leprae pathogenesis Incubation period – 9 months to 20 years (!!) Multiple forms of disease Tuberculoid (paucibacilliary) – CMI limits M. leprae growth – Multiplication at site of entry → Schwann cell invasion – Lymphocyte recruitment partially responsible for nerve damage → loss of sensation. – Lesions heavily infiltrated, but no caseation like in TB – Strong CMI response – few bacteria in lesions Misch et al, 2010, MMBR  M. leprae pathogenesis Lepromatous (multibacilliary) – Impaired CMI response - microbes proliferate within macrophages – Large numbers of M. leprae in macrophages – Extensive penetration of M. leprae to distal sites → loss of bones, fingers, and toes – Associated with disfiguring lesions – Symptoms and damage associated with impaired CMI Exact mechanism of nerve damage still remains poorly understood Treatment with dapsone+rifampicin+ clofazimine for 6-12 months Misch et al, 2010, MMBR  M. leprae growth and culture Very slow growing – Doubling time 12-14 days (!!) Growth at 33C – Tropism for peripheral nerves (lower temp) – Tropism for Schwann cells and macrophages M. leprae cannot be grown in the laboratory – Intracellular pathogen – Grown for study in 9-banded armadillos (!!) 9 months to get enough bacteria to study Also in footpads of athymic nude mice  M. leprae evolution/genomics Genomics – Highly reduced genome – 3.3Mb c.f. other Mycobacteria, >5Mb – Very low genetic variability among strains – Many pseudogenes suggests evolution towards obligate intracellular niche Cole et al, 1998, Nature Pseudogenes in many metabolic pathways – needs host cells to provide major nutrients Han & Silva, 2014, PLoS NTD  Non-tuberculous/atypical mycobacteria Group of organisms other than Mtb that do not cause leprosy Ubiquitous in the environment – Live in soil and water systems – Most NTM are non-pathogenic – 80-90% of NTM infections are pulmonary disease – Infections acquired from environment → not normally person-to-person transmission Includes >150 species Baldwin et al, 2019, PLoS NTD  Pulmonary NTM infections Most often seen in patients with lung diseases/immunosuppression – e.g. cystic fibrosis, bronchiectasis, COPD, etc – However, also seen in immunocompetent individuals Most establish granulomatous infections in lung Infections are rare but serious and difficult to treat – NTM patients have high risk of reinfection Most frequently caused by: – M. avium complex (SG) – M. kansasii (SG) – M. abscessus (RG)  M. avium complex (MAC) MAC = group of organisms comprising: – M. intracellulare – M. avium Opportunistic pathogen – Generally only seen in immunocompromised hosts – Can also cause disseminated disease Increasing incidence over last 20 years (~16/100,000) Treatment = 12-18 months of antibiotic therapy – Side effects common, treatment cost is high  Mycobacterium abcessus Emerging as a significant cause of NTM pulmonary disease in immunocompromised individuals Produces biofilms – Provides protection inside lungs of COPD/CF patients – Also protects from drug treatment Intracellular pathogen – survives in macrophages Also causes skin infections – Direct contact with contaminated material – linked to acupuncture, tattooing, liposuction, cosmetic surgery  Mycobacterium abcessus Increasingly associated with cystic fibrosis patients – 13% of CF patients have NTM infection Divided between MAC and M. abscessus (3:1) – M. abscessus multiply drug resistant Very difficult to treat in CF population – Requires >12 months antibiotics – In many instances, cannot be cleared Lifelong antibiotic treatment Lung transplant contraindicated in patients with NTM infection Cutaneous NTM infections Most frequently caused by: – M. marinum (SG) – M. ulcerans (SG) – M. chelonae (RG) – M. abscessus (RG) – M. fortuitum (RG) High levels of antibiotic resistance Water is most common source of infection – Including municipal water sources – High chlorine tolerance – Biofilm formers  Mycobacterium marinum Causes “fish tank” granulomas – Pathogen of fish and humans – Caused by direct contact of skin with contaminated source Causes granulomatous skin lesions – Rarely systemic or life threatening M. marinum is slow growing – Optimal temp of 30 – 32 C – Closely related to M. ulcerans  Mycobacterium chelonae Often presents as disseminated disease – Multiple lesions at once Often purulent with necrotic debris – Localised form also possible More common after trauma/surgery Can involve bone/joint infections – Pulmonary infections rare Mainly in immunosuppressed individuals High levels of resistance to standard anti-mycobacterial drugs  Mycobacterium chimaera Associated with infection during heart bypass surgery – Often infection of replacement heart valves – Can also be disseminated Risk is low, BUT – 50% mortality – difficult to treat Slow growing, no diagnostic tests – Median incubation period = 17 months – Diagnosis can be up to 5 yrs later  M. chimaera HCU outbreak First recognized in 2012 in Switzerland All patients had heart bypass surgery – Uses heater-cooler units to maintain blood temperature during open heart surgery – Contaminated units produced M. chimaera containing aerosols – Contaminated operating field Cases occurred across geography and time – All cases genetically linked Riccardi, 2020, J Infect Chemother – All hospitals had used one brand of HCU – Testing identified contaminated factory equipment Treatment – 12 months+ of rifampicin/ethambutol/a macrolide  Anti mycobacterial drugs Isoniazid – Prodrug activated by mycobacterial enzyme KatG – Binds tightly to InhA → blocks fatty acid synthesis and mycolic acid synthesis – Bactericidal in rapid growers, bacteriostatic in slow growers Ethambutol – Inhibits arabinosyl transferase (embCAB operon)→ disrupts arabinogalactan biosynthesis – Inhibits mycobacterial cell walls  Anti mycobacterial drugs Pyrazinamide – Prodrug activated by mycobacterial enzyme PncA (pyrazinamidase) – Diffuses into granulomas – Little activity against growing cells, primarily active against persister cells Other drugs, depending on Mycobacterium species – Aminoglycosides (amikacin/streptomycin), quinolones (moxifloxacin), rifampicin, macrolides (clarithromycin/azithromycin)  New anti mycobacterial drugs Bedaquiline – Newest anti-TB drug (2012), diarylquinoline family – Inhibits mycobacterial ATP synthase – novel mechanism of action Binds to C-ring, stopping rotation and inhibiting catalytic activity of “headpiece” – Bactericidal – active against replicating and dormant organisms – Used as part of “new” anti-TB regimens  Anti mycobacterial drugs Delaminid/pretomanid – Nitroimidazoles – Inhibits cell wall synthesis (blocks mycolic acid synthesis) – Approved for MDR-TB Telacebec (Q203) – Recently completed phase 2 (2020) for TB → positive results! – Targets cytochrome bc1 → depletion of ATP from cells – Highly active against M. ulcerans – mouse lesions were culture negative after only 1 week of treatment Anti mycobacterial drugs  Summary Mycobacterial pathogens are still a major problem today – M. tuberculosis = Tuberculosis – M. leprae = Leprosy – NTM = Pulmonary or cutaneous diseases Many drugs used to treat mycobacteria are specific for mycobacterial targets