W3 Mycobacteria Definition · Unicellular rod-shaped micro-organisms; obligate aerobes; non-motile; non-capsulated; non-sporulating;2-4 micrometres length X 0.2- 0.5 micrometres in width · Will survive under anaerobic conditions but wont grow in them . Tend to be hydrophobic as a result tend to clump up · Many species of Mycobacterium exist; only a few cause disease in humans · Phylum - Actinobacteria (G+C content); filamentous o Family - Mycobacteriaceace o Genus-Mycobacterium . Many important species are slow growing (12- 20 hours) · Cell wall comprises high lipid content (unlike gram +ve/-ve bacteria) o Means they are hydrophobic so use detergents to prevent clumping Unique cell wall structure POMM DAT SGL POIM PAT DAT Characteristic "free" lipids Outer membrane (MOM) MOM MA "Bound" mycolic acids Arabinogalactan- peptidoglycan & GalNHG Periplasm g& Linker unit ~> Succinyl Periplasm LAM Inner membrane (MIM) mr Ac/Ac_PIM, @DPG MIM 1 Ac/AC_PIMa Features of cell wall (60 % lipid): · High glycolipid content e.g. Mycolic acid · Other lipids include surface acyl lipids; lipoarabinomannan (LAM)- peptidoglycan does exist within the membrane structure but it anchored to LAM; phosphatidy inositol mannosides (PIM); cord factor (TDM-trehalose dimycolate) Why is this important medically? . Intracellular survival due to TDM o When inhale this mycobacterium and ingested by alveolar macrophage, this lipid can stop the lysosome from fusing to the phagosome = no phagocytosis= hijack macrophage · Confers resistance (e.g. many antimicrobials, heat, chemicals, drying, stains) · Mycobacteria are acid fast · Special stains required to visualise mycobacteria Ziehl-Neelson stain for acid fast bacteria · Stain with hot concentrated carbol fuschsin and (all bacterial cells stained pink at this stage) · De-stain with 1% acid alcohol (hydrochloric acid/ethanol) OR 20% H2SO4 (mycobacterial cells remain pink, all others colourless) · Counterstain with methylene blue (mycobacterial cells remain pink, all other bacteria and cells e.g. WBC stain blue) Infections caused by Mycobacteria Disease Symptoms Tuberculosis (TB) Species of Mycobacterium M. tuberculosis (focus of today's lecture) M. bovis Often asymptomatic; pneumonia-like presentation (weight loss, temperature, cough, blood in sputum) As above M. avium intracellulare Tuberculosis (TB); acquired from consumption of unpasteurised milk Disseminated TB in immunocompromised patients eg. HIV M. leprae (Hansen's bacillus) Leprosy Lung infection and spread to bones, joints, blood, renal system, meninges; frequently results in death Folded lesions on face and limbs, disfiguration, loss of peripheral nerves, secondary infection 21st century tuberculosis · 1/3 of the worlds population predicted to have TB · 8.4 million new cases per year · 1.5 million deaths per year · Uk- 6000 annually Predisposing factors of TB infection
W3 · Close contact with large populations of people i.e. schools, nursing homes, dorms, prisons, etc · Poor nutrition · Iv drug use · Alcoholism . HIV infection is the MAIN predisposing factor for TB infection. 10% of all HIV-positive individuals have TB (400x the rate associated with the general public) TB infection: droplet nuclei · Droplet nuclei (5um, approx. 3 bacilli- minimum infective dose) · Aerosolised: Talking for 5 minutes: 3000 o Coughing:3000 o Sneezing: 3000 up to