MYCOBACTERIA - TB MYCOBACTERIA DEFINITION · Unicellular rod-shaped micro-organisms · Obligate aerobes (do survive under anaerobic conditions as well as aerobic) · Non-motile (no flagella) · Non-capsulated · Non-sporulating . 2-4 mm length X 0.2-0.5 mm width · Many species of Mycobacterium exist - only a few cause disease in humans · Phylum = Actinobacteria (High G+C content) = filamentous - Family = Mycobacteriaceae - Genus = Mycobacterium · Many important species are slow growing - (generation time: 15-20 hrs) · TB takes 2-3 weeks for culture to grow · Cell wall comprises high lipid content (unlike Gram positive / negative bacteria) = acid-fast bacteria HOW MYCOBACTERIA DIFFER FROM OTHER BACTERIA - UNIQUE CELL WALL Features · High glycolipid content (e.g. mycolic acid) · Other lipids = surface acyl lipids, LAM, PIM, cord factor (TDM) - stops lysosome and alveolar phagosome binding therefore essential for survival · Why is this important medically? · Intracellular survival · Confers resistance (e.g. antimicrobials, heat, chemicals, drying, stains) - need specialist method in order to get rid of infection · Waxy cell wall stops the bacteria drying out Ziehl-Neelson Stain - special stain required to visualise · Hot concentrated carbol fuchsin - all bacterial cells become pink · Destain with 1% acid-ethanol / 20% hydrogen peroxide - mycobacterial cells remain pink, all others colourless · Counterstain with methylene blue - mycobacterium stay pink, all other bacteria and cells go blue (including WBCs) · They aggregate so use mild detergent to reduce hydrophobicity - always have a little bit (why we don't see filaments) TYPES OF INFECTIONS CAUSED BY MYCOBACTERIA · M. Tuberculosis (TB) - often asymptomatic, pneumonia like presentation (weight loss, temp, cough, blood in sputum) . M. Bovis (TB) - acquired from the consumption of unpasteurised milk (same symptoms as above) . M. Avium intracellulare - disseminated TB in immunocompromised patients - lung infection which turns systemic and usually causes death · M. leprae (Leprosy) - folded lesions on face and limbs, disfiguration , loss of peripheral nerves, secondary infection · Carried by the armadillo History TUBERCULOSIS - TB
· 1720 - Benjamin Marten described 'consumption' · 1882 - Koch discovered cause of 'consumption' was M, tuberculosis · Granville's mummy (600BC) - in 1825 they did a post mortem and diagnosed ovarian cancer · 21st century (UCL) - TB DNA identified in Granville's mummy (now correct diagnosis) 21st Century Epidemiology · 1/3 of the world population is predicted to have TB - latent (asymptomatic) · 8.4 million new cases/year · 1.5 million deaths per year UK trends · 1950 = 50000 · Mid-1980s = 6000 · 1987-1990 = 7000 · 2010 = 9000 · Now = 6000 Predisposing factors of TB infection · Close contact with people · Poor nutrition · IV drug use · Alcoholism · HIV infection - main predisposing factor (10% of HIV sufferers have it) TB INFECTION · Droplet nuclei (5um, approx 3 bacilli) · Aerosolised · Talking for 5 mins = 3000 · Coughing = 3000 · Sneezing