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Lecture

Mycobacteria, Spirochetes, Chlamydia, Myoplasmas, and Fungal Infections.docx

4 Pages
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Department
Health Sciences
Course Code
HSS1100
Professor
Franco Pagotto

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Mycobacteria • Causative agents of tuberculosis and leprosy  • Waxy coat  ­ NO Gram stain ­ Resistant to disinfectants  • Acid­fast bacilli ­> Resist decolorisation  • Use Ziehl­Neelsen staining technique: 1. Ziehl­Neelsen carbol fuchsin to the slide for five minutes while applying heat.  (dissolve lipid cell wall) 2. Follow with a gentle wash with water to cool the slide.  3. Acid alcohol is now added to decolorize the slide.  4. Wash the slide in water again and counterstain with methylene blue for 1­2  minutes  1) Mycobacterium tuberculosis • Chronic slow­progressing pulmonary infection; transmission by aerosol droplets  • Obligate aerobe, facultative intracellular parasite  • 4­6 WEEKS to see colonies on a plate • Lowenstein­Jensen medium • Use microscopy of  sputum smears as first line of diagnosis  • Leading cause of death world­wide form a single infection (Bacteriology, Kenneth Todar,  2005) • Affects1.7billion/year • Declining in US  • Infection develops in stages  A) Primary Tuberculosis 1. Aerosol inhalation 2. Bacteria multiplication in alveoli 3. Macrophage ingestionof bacilli and formation of 1o complex 4. Foci of infection in lungs (may be spread to kidneys, bones, meninges) 5. CMI is fully active, infection is stopped (majority of cases) ~6 weeks 6. Some bacilli survive, reactivation several years later B) Post­primary tuberculosis • Late reactivation of lesions in lungs, kidneys, bones etc • 5% of cases; higher in patients with AIDS • Chronic infection Immunity in Tuberculosis • Cell mediated immunity is most important (T­cells)  • Mantoux test  1) Tuberculin solution is injected INTRADERMALLY, wait 48­72 hrs,  check for induration  2) Record diameter of induration  a) >10mm POSITIVE  b) 5­9 mm Doubtful, maybe cross reaction with other  Mycobacteria  c) <4mm NEGATIVE  **A positive test does not necessarily mean there is currently an active infection**  2) Mycobacterium leprae • Causes leprosy  • 2 kinds: 1. Tuberculoid leprosy: visible nerve enlargement, few erythmatous plaques, few  bacilli in infected tissues, but many lymphocytes and granulomas; low  infectivity  2. Lepromatous leprosy: no visible nerve enlargement, many erythromatous  nodules, many bacilli in infected tissue; high infectivity • Rarely found in developed countries  Spirochetes 1) Treponema pallidum • Syphilis • Gram negative, helical bacteria  • Unculturable in vivo  • Use dark field microscopy; almost invisible under Gram stain, Geimsa stain and Ziehl­ Neelsen  A) Syphilis Primary syphilis • Appearance of chancre 3­4 weeks after infection  • Fluid from lesion contains bacteria seen under dark­field microscopy  Secondary syphilis • 6 weeks after appearance of chancre • Generalized or local rash • Mucosal lesions with many treponemes  • Spontaneous remission may occur after 1 or 2 phase  Latent syphilis • No symptoms of infection  • Non­transmittable after 4 years • BUT congenital infection may occur  Late syphilis  • Ob
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