Lect 14 Flashcards
(35 cards)
Mycobacterium tuberculosis: reservoir and transmission
- humans are only reservoir
- transmission: aerosol
MTB Strains vary in antibiotic susceptiblity. name the strains
MDR strains - multi-drug resistant XDR strains - extensively drug resistant
MTB Bimodal Age Distribution of disease. Name the ages and also what type of dissemination occurs in these patients
- Infants and Older Adults
- Infants and Immunocompromised - Hematogenous dissemination Can result in meningitis and other symptoms
- Older - Failure of immune system - Possible reactivation of latent infection
MTB initial infection risk factors
- close contact with TB case: • Many children become infected by caregivers
- Residence in long-term care facility
- Low income/inner city housing
- Alcoholism or IV Drug Use
- Diabetes mellitus (30% increase over lifetime)
- Silicosis - pneumoconiosis- inhalation silica dust
- Immunosuppression
Name the three species that produces human tuberculosis
- mycobacterium tuberculosis
- mycobacterium bovis
- mycobacterium aficanum
which mycobacterium is the source of the BCG vaccine
mycobacterium bovis
MTB
- shape
- motility
- oxygen?
- bacillus
- non motile
- obligate aerobes
MTB is killed by what process that we do to milk
- pasteurization
- *heat sensitive
where does MTB grow
- intracellular growth - alveolar macrophages
MTB undergo what type of staining
- MTB cells resist normal gram stain: acid fast bacilli
- harsh treatment is used: ziehl-neelsen or Kinyoun stains
- MTB cells, once stained, will not decolorize
describe cell wall of mycobacterium tuberculosis
- outer layer: mycolic acid
- inner layer: peptidoglycan
- **cell wall Influences staining behavior, produces slow growth phenotype and confounds antibiotic therapy
MTB virulence factors
- No classic virulence factors or toxins
- structure enables it to persist as an intracellular pathogen
- mycolic acid: prevent dehydration and may resist H2O2
-
cord factor
- Mycoside – glycolipid Mycolic acid + disaccharide
- lipoarabinomannan: Inhibits cell-mediated immunity
MTB infection potential outcomes
- immediate resolution
- primary disease
- progressive primary (active disease)
- latent infection
- endogenous reactivation/secondary disease
how does MTB cause cell and tissue destruction
- After phagocytosis by macrophages, MTB specifically prevents fusion with lysosomes while allowing nutrient-containing vesicles to merge.
- Innate and cell-mediated host immune responses to MTB produces selfdestruction of cells and tissues
what structure becomes evident 2-6 weeks after MTB infection
- granulomas: areas surrounded by macrophages, fibroblasts, and collagen fibers harboring viable MTB cells
- over time, can form fibrotic tubercle and calcify-> tubercles or Ghon bodies.
Does person infected with latent TB able to spread disease
- bacteria remain viable in lesions but inactive
- patients have no symptoms
- no risk to spread disease
what happens to a patient when latent TB becomes reactivated-> secondary TB
- Granulomas: Erode and discharge TB bacilli into bronchi (infectious)
- Erode blood vessel – hematogenous spread to other body sites – TB can involve any organ
- signs and symptoms are present; patient is infectious
- cough, weight loss, fatigue, fever, night sweats, chest pain
what is miliary tuberculosis
- results from lymphohematogenous spread of primary infection or via a latent focus with subsequent spread
- **massive spread of agent
What means are available to help aid diagnosis of TB
- skin test
- xray consistent with TB
- sputum stain/broth culture to detect acid fast bacteria
describe Serial screening programs
- Use purified MTB protein derivative (PPD) in tuberculin skin test (Mantoux skin test)
- Small amount of antigen injected under the skin, size of induration measured after 48-72 hours
- Boosters (persons with earlier infection with minimal reaction to PPD) are identified by quick second administration
what can cause a false positive on TB skin test
BCG recipients and those infected with NTM may react as false positives
length of treatment for active TB disease
extended duration (6-9 months), multi-drug regimen requiring patient compliance
treament for latent TB
Isoniazid (9 months)
Mycobacterium avium complex (MAC)
- gram status
- oxygen?
- where is it found
- gram positive
- aerobic
- ubiquitous
- water, soil, plants
