Acid Fast Bacteria Flashcards
Process for acid fast staining
Carbolfushsin (red), heat, acid alcohol, methylene blue counter stain.
Acid fast organisms are red
Why are HIV patients at high risk for TB?
Reduced cell mediated immuntiy
Basic description of Mycobacterium tuberculosis
Acid fast
Obligate aerobe
Grows slowly
Hydrophobic lipid cell wall
What are the virulence factors of TB?
1) mycolic acid / mycosides - all below are mycosides
2) cord factor (damages mitochondria, releases tumor necrosis factor)
3) sulfatides- prevent phagocytosis
4) wax d- enhances antibody formation
Pathogenesis of TB
Inhaled via lungs, survives in macrophages (facultative intracellular growth) and invades other sites
Cell mediated immunity, necrosis of lung tissue
Term for necrosis of lungs from tb
Caseous necrosis
How long does it take for hypersensitivity reaction in PPD test to develop
48 hours
What are the cut points for TB ppd test induration
5 mm- HIV positive or immunosupressed
10 mm- from high incidence country, HCP, prior incarceration, high risk medical condition (diabetes)
15 mm- all others
What does a positive PPD result mean?
Person was exposed and infected at some time in the past
Positive for active, latent, and cured
What may cause a false positive TB ppd?
Bacillus calmette-guerin (BCG) vaccine
What may cause a false negative PPD test?
Anergic patients (lack normal immune response due to steroid use, malnutrition, AIDS, etc
Second test for tb
interferon gamma release assay (IGRA)
What is the risk of developing TB if infected with mycobacterium tuberculosis?
10 %
Stages of tb
1) primary (subclinical infection in lungs
2) latent - cell mediated immunity walls off bacteria
3) secondary or reactivation TB
Transmission of TB
Aerosolized droplet nuclei from adult with pulmonary tb
Describe the asymptomatic primary infection of TB
Tubercles form in lungs (walled off bacterium) and calcify (ghon focus)
Calcified tubercle in middle or lower lung zone
Ghon focus
Ghon focus accompanied by perihilar lymph node calcified granulomas
Ghon complex
Who is typically effected by symptomatic primary TB?
Children
Elderly
Immunocompromised
Clinical symptoms symptomatic primary tb
Chest radiograph shoes enlargement if mediastinal or hilar lymph nodes, sometimes chest infiltrates
Usually resolves with formation of tubercle granulomas
Most common site for tuberculosis reactivation
Pulmonary tb
Clinical symptoms of pulmonary tb
Chronic low grade fever, night sweats, weight loss, productive cough that may have blood
Describe pleural and pericardial TB infections
Fluid collection around the lungs or heart
Most common extra pulmonary tb infection
Lymph node infection, called scrofula
Another name for secondary TB if kidneys
Sterile pyuria
What is the disease causes by secondary TB in the skeleton?
Pott’s disease
How can secondary TB impact the joints?
Chronic arthritis in 1 joint
How can secondary TB effect the CNS
Meningitis and granulomas of the brain
Form of secondary TB, usually in children and elderly, where tiny
Millet seed shaped tubercles (granulomas) are disseminated all over the body
Military tuberculosis
What are the diagnostic test for tb?
Chest x-ray
Sputum acid fast stain and culture
Rapid molecular detection
Describe resistance in MDR-TB
Resistant to isoniazid and rifampin
What is the resistance in XDR-TB
Resistant to isoniazid and rifampin, a fluoroquinolone, and an injectable agent (like and aminoglycosides)
Basic description mycobacterium leprae
Acid fast rod
Impossible to feel on artificial media
Transmission of mycobacterium leprae
Respiratory secretion or skin lessions, unknown why certain people are susceptible
Types of leprosy based on severity
Lepromatous leprosy (most severe)
Tuberculosis leprosy
Borderline leprosy
Expansive group of acid fast organisms that are ubiquitous in the soil and water
Nontuberculosis mycobacteria (NTM)
Opportunistic Nontuberculosos mycobacteria that is common in people with AIDS
Mycobacterium avium-complex (MAC)
CD4 Cell count typically associated with mycobacterium avium complex infections
<50 CD4 per mm^3
Symptoms Mycobacterium avium-complex
Fever
Weight loss
Diarrhea
General malaise
Increase in alkaline phosphatase in routine labs
Organism that most commonly causes NTM lung diesase
Mycobacterium avium-complex
In an immunocompromised host, what illness can mycobacterium avium complex cause?
- Upper lung cavitary disease in elderly smokers
- Middle and lower lung nodular and bronchial disease in middle aged female non-smokers
- Lymphadenitis in children
What diseases can Mycobacterium kansasii cause?
- Upper lung cavitary disease
- Disseminated disease in immune compromised patients
Diseases caused by mycobacterium abcessus
- Pulmonary disease
- Skin, soft tissue, and bone disease
Diseases caused by mycobacterium fortuitum
Skin, soft tissue, and bone disease
What NTM is a common lab contaminant?
Mycobacterium fortuitum
What mycobacterium is associated with foot baths
Mycobacterium fortuitum
What diseases does mycobacterium chelonae cause?
- Skin, soft tissue, bone disease
- Disseminated disease immunocompromised
- Keratitis associated with contact use
What NTM is associated with fish tanks and is usually found in fresh and salt water
Mycobacterium marinum
What disease does mycobacterium marinum caus
Fish tank granuloma
What disease does mycobacterium ulcercans cause
Buruli ulcers (progressive necrotic skin ulcerations)
This NTM is found in tropical rain forests
Mycobacterium ulcerans
This species of MAC caused two outbreaks in prosthetic valve infections And disseminated infection tied to heating and cooling units in cardiac bypass procedures
Mycobacterium chimera
