Medical Microbiology Bacteriology Lecture 31 PDF

Lecture 31 - Tuberculosis 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 tuberculosi...

Lecture 31 - Tuberculosis 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 State the key features of tuberculosis disease and describe key pathogenic features of M. tuberculosis  The genus Mycobacterium Member of the Actinobacteria – 190 species within genus Mycobacterium – Includes major human pathogens Mycobacterium tuberculosis Mycobacterium leprae – Species are quite diverse O’Neill et al, 2015, PLoS Pathogens, Core genome tree Aerobic, rod shaped bacteria Stain acid fast – Use Ziehl-Neelsen stain – Variable Gram stain 5  Mycobacterial cell wall Unusual cell wall Brown et al, 2015, Nature Rev Micro Thicker cell wall than other bacteria – Hydrophobic/waxy – Rich in mycolic acids/mycolates – Outer lipids linked to peptidoglycan by arabinogalactan 6 – Several cell wall pathways unique to mycobacteria  Mycobacterial lipids 30-60% of cell dry weigh is lipids! 30% of M. tuberculosis genome devoted to lipid metabolism/synthesis Many lipids unique to each mycobacterial species Mycobacterial lipids are important for Brown et al, 2015, Nature Rev Micro both structure and virulence – Can activate or suppress the immune system – Help to survive inside macrophages – Help to evade immune system – Stimulate granuloma formation https://labmedicineblog.com/tag/mycobacterium/ Mycobacterial cell envelope - https://www.youtube.com/watch?v=yuHUikQy2vk  The genus Mycobacterium Divided into slow growing and rapid growing – Even rapid growers can take up to 7 days – Some slow growers can take months to form visible colonies Often pigmented – Usually yellow, orange, etc Many species free living environmental organisms – Except M. tuberculosis and M. leprae 8  The genus Mycobacterium Pathogens in the genus Mycobacterium – M. tuberculosis – M. leprae – M. ulcerans – M. avium – M. abscessus – M. chimaera M. tuberculosis is human restricted Many other mycobacterial pathogens are opportunists  Mycobacterium tuberculosis Causative agent of human tuberculosis – Humans = only known host/reservoir Discovered 1882 by Robert Koch Primarily infects lungs – Can disseminate to tissues as well – Intracellular pathogen Slow growing – Divides every 18-24 hrs c.f. E. coli ~20 mins doubling time – 3-4 weeks to get colonies Needs special media to grow (egg-based or defined) 10 Cells are resistant to dessication, mild disinfectants M. tuberculosis life cycle Cambier et al, 2014, Cell M. tuberculosis pathogenesis 12 Ehrt et al, 2018, Nat Rev Micro  M. tuberculosis virulence factors Complex lipids – Phthiocerol dimycocerosates (PDIMs) Protect against ROS inside macrophages – Phenolic glycolipids (PGLs) Only some clinical isolates make PGLs Dampen host immune response by inhibiting pro-inflammatory cytokine release – Sulfolipids (SLs) inhibit phagosome–lysosome fusion and acidification in infected murine macrophages  M. tuberculosis virulence factors PE/PPE family proteins – Have conserved N-terminal motifs – Pro-Glu (PE) or Pro-Pro-Glu (PPE) residues – Many secreted by type VII secretion systems – In M. tuberculosis they comprise nearly 10% of genomic coding potential – Roles uncertain - interact with host immune system? Outer membrane small- molecule channels that enable nutrient uptake? T7SS – Five type VII secretion systems (T7SS) EsxA secretion system-1 (ESX-1) to ESX-5 – ESX-1, ESX-3 and ESX-5 required for the full virulence of M. tuberculosis – Effectors have YXXXD/E motif or a WXG motif “transport signal” – Involved in delayed phagosome maturation, phagosome rupture, cellular necrosis, etc https://www.nature.com/articles/s41579-021-00560-5  Extrapulmonary TB Dissemination of M. tuberculosis outside of lungs – More common in immunosuppressed individuals/HIV patients – ~20% of all TB cases Can occur in: – Pleural cavity (pleural TB) – Preitoneum (peritoneal TB) – Nervous system (TB meningitis) – Genitourinary system (urogenital TB) – Bones, esp spine (Pott disease) – Multiple sites simultaneously (military TB) 15  Tuberculosis epidemiology In 2019: – 10 million new cases of TB disease co-infection with HIV = 10% – 1.5 million deaths – 2 billion with latent TB? Greatest disease burden in low/middle income countries WHO, Global Tuberculosis Report, 2020  Tuberculosis epidemiology Incidence Deaths WHO, Global Tuberculosis Report, 2020 Tuberculosis epidemiology WHO, Global Tuberculosis Report, 2020  Where did M. tuberculosis come from? Origins of M. tuberculosis still uncertain Emerged as a pathogen from environmental mycobacteria – Stepwise adaptation to intracellular environment – Survival in protozoa key for evolution? Similarity to survival in macrophages – Downsizing of genome combined with HGT important? Galangal, Nat Rev Genet, 2014  Where did M. tuberculosis come from? Humans thought to have acquired TB from animals during Neolithic period – Camp-fire hypothesis → simultaneously promoted social interactions and smoke-induced lung damage – But M. bovis has smaller genome than M. tuberculosis Suggests humans TB is ancestor of bovine TB “Out of Africa” hypothesis – Oldest relatives of Mtb found exclusively in Horn of Africa – Africa has largest diversity of Mtb lineages  M. tuberculosis vaccination M. bovis BCG vaccine – first used in 1921 – Protection is highly variable overall decreases risk of infection by 20-50% – Duration of protection is unknown – conflicting studies 14 vaccine candidates in clinical trials – Best so far is M72/AS01E – recombinant fusion protein of 2 x M. tuberculosis antigens In phase II, ~50% efficacy in adult TB+ve population 21  M. tuberculosis diagnosis Microscopy and culture still main diagnostic tools for active disease – Culture = prone to contamination, >4-6 weeks to result – Microscopy = requires sputum, not very sensitive New tools – GeneXpert – cartridge based, PCR test – Line-probe assays (LPAs) to detect resistance Can detect multiple resistance markers Take longer, more complicated than GeneXpert No simple, effective rapid POC test available so far  M. tuberculosis treatment TB treatment – Multiple drugs given simultaneously over a long period – 2 months of isoniazid/rifampicin/ pyrazinamide/ethambutol + 4 months of isoniazid/rifampicin – If resistance, 8-9 months: fluoroquinolone/ clofazimine/ethambutol/pyrazinamide/isoniazid/bedaquilline/ prothionamide → 7 drugs!!! 23 new drugs in clinical trials – New and repurposed “old” drugs Drug resistant variants emerging all over the world… https://www.compoundchem.com/2017/03/24/tuberculosis/  M. tuberculosis drug resistance Multidrug resistant-TB (MDR-TB) – Resistant to isoniazid and rifampicin – ~480,000 cases in 2018 – 57% success rate in cure Extensively drug resistant TB (XDR-TB) – Resistant to isoniazid and rifampicin, to a fluoroquinolone and an aminoglycoside – ~48,000 cases in 2018 – 43% success rate in cure 10 million cases of TB per year – (fill in your own summary here)… – – –