Mycobacterium Tuberculosis Flashcards
Microbiology of Tuberculosis?
A.Aerobic, non-spore forming, non-motile bacillus
B.A mycolic acid cell wall
C.Slow generation time
D.Acid fast positive with Ziehl Neelsen stain
E.Fluoreses positive with auramine fluorochrome stain
F.Lacks pigment
G.Produces niacin and heat sensitive catalase
H.Reduces nitrates
I. Sensitive to INH
Mode of spread of tb? Risk of infection?
– Mode of Spread • Droplet nuclei of small size and high number (3000 per cough) • Prolonged exposure • Fomites not important
– Risk of infection • Infectiousness of source case (smear positive 50% conversion) • Closeness of contact
Risk of progression of infection to disease for TB? Influence of chemotherapy on infection spread?
– Risk of progression of infection to disease • Varies with age (under 3, young adults, elderly) • Varies with intensity of exposure • Increased risk in debilitated
– Influence of chemotherapy on spread of infection • Noninfectious after two weeks
Pathogenesis of PD prior to a positive PPD?
• Pathogenesis (prior to positive PPD)
– Droplet nuclei inhaled and deposited lower lobes of lung (airflow greatest)
– Unstimulated macrophages ingest organisms
– Infected macrophages to regional nodes (hilar, mediastinal)
– Lymph hematogenous dissemination • Extrapulmonary (CNS, kidney, bone, etc.) • Secondary pulmonary (apical posterior lung)
– Factors influencing fate of infection • Age of patient • Underlying immunocompromised states
Explain the immunopathology of TB?
–Small inoculi bypass mucocilia to alveoli
–Nonsensitized alveolar macrophages ingest organisms • Proliferate intracellularly
–T lymphocytes activated by macrophage antigen complex:
- Replication
- Production of lymphokines – Activate other T lymphocytes – Activate macrophages to produce lytic enzymes (cydal)
- Activated macrophages – Epithelioid cells – Langerhans giant cells (granuloma formation)
- Increase population of activated lymphocytes – Tissue hypersensitivity (positive PPD) 6-14 weeks after infection
What might the antigen load and tissue hypersensitivity tell you about whats going in the lung?
–Antigen load low – tissue hypersensitivity high - Granuloma
–Antigen load and tissue hypersensitivity high – Caseous necrosis
Ppl who are high risk for TB?
- Persons with HIV infection
- Close contacts of known infectious tuberculosis
- Persons with other medical risk factors which increase the risk of tuberculosis once infection has occurred
- Foreign-born persons from high prevalence countries
- Medically underserved low-income populations, including high-risk minorities (especially Blacks, Hispanics, and Native Americans)
- Alcoholics and intravenous drug users
- Residents of long-term care facilities, such as correctional institutions and nursing homes
TB is a systemic disease and it may affect what areas of the body?
• Lungs • Pleura • Central Nervous System • Lymphatic system • Genitourinary system • Bones and joints • Any other body organ or tissue
Groups to screen with a tuberculin skin test?
- Persons with HIV infection
- Close contacts of known infectious tuberculosis cases
- Persons with other medical risk factors which increase the risk of tuberculosis once infection has occurred
- Foreign-born persons from high prevalence countries (e.g., those from Asia, Africa, and Latin America)
- Medically underserved low-income populations, including high-risk minorities (especially Blacks, Hispanics, and Native Americans)
- Alcoholics and intravenous drug users
- Residents of long-term care facilities, such as correctional institutions and nursing homes
- Other populations which have been identified locally as having an increased prevalence of tuberculosis, e.g., health care workers in some areas
Medical risk factors that increase the risk of developing TB once the infection has been acquired?
- HIV infection
- Silicosis
- Abnormal chest radiograph showing fibrotic lesions
- Diabetes mellitus
- Prolonged corticosteroid therapy
- Immunosuppressive therapy
- Hematologic and reticuloendothelial diseases (e.g., leukemia and Hodgkin’s disease)
- End stage renal disease
- Intestinal bypass
- Post-gastrectomy
- Chronic malabsorption syndromes
- Carcinomas of the oropharynx and upper gastrointestinal tract
- Ten percent or more below ideal body weight
Explain a TB skin test?
- Use intradermal Mantoux test
- 0.1 ml of 5 TU PPD tuberculin
- Read 48-72 hours after application
- Needles should not be recapped, bent, broken, or removed from syringes
- Gloves are not necessary
Classification of TB skin test, reaction of 5mm is positive in?
A reaction of ≥ 5mm is positive in:
- Close contacts to patients with infectious tuberculosis
- Persons with HIV infection
- Persons who have chest radiographs with fibrotic lesions
In a TB skin test a 10mm lesion is positive in?
A reaction of ≥ 10mm is positive in:
- Persons with medical risk factors which increase the risk of tuberculosis once infection has occurred
- Foreign-born persons from high prevalence countries
- Low-income populations, including high-risk minorities
- Intravenous drug users
- Residents of long-term care facilities, such as correctional institutions and nursing homes
- Other high-risk populations indentified locally e.g., health care workers in some areas
A reaction of 15mm is positive in?
• Persons with no additional risk factors for tuberculosis
TB diagnosis? what is essential?
Examination for tuberculosis normally includes:
- History
- Physical examination
- Mantoux tuberculin skin test
- Chest radiograph
- Bacteriologic/histologic
- Examination for smear and culture
A positive bacteriologic culture for M. tuberculosis is essential to confirm the diagnosis of tuberculosis
