Mycobacteria: TB, Leprosy, and Atypicals Flashcards
What is the most common infectious cause of mortality worldwide? How much of the population is infection? How was it treated when it was on the decline?
M. tuberculosis
four-drug regimens featuring isoniazid!!!!!
But now have multidrug resistant and extensively drug resistant strains - in immunosuppressed populations, infectious state continues
How do you stain M.tuberculosis? Why?
Acid fast; TB gram stains very poorly, mycolic acid is waxy and hard to stain.
Keep in mind that antibiotics prevent NEW peptidoglycan from being synthesized and that rapidly growing bacteria are easier to target. Slow growing bacteria are harder to kill.
What are the steps of the acid fast stain?
1- Cover smear w/carbolfuscian. Boil w/ extra stain for 10 minutes 2- decolorize with acid-alcohol 3- water 4- counterstain with methylene blue 5- rinse and blot dry
sputum sample lumpy places = cords, characteristic of TB
- What is unique about M. tuberculosis growth?
- What is the host and reservoir?
- Where can they grow in humans?
- Toxins?
- What is their mechanism of drug resistance?
- Grows in vitro, but slowly (even in human host!), requires special nutrients
- Humans
- Intra or extracellular
- NO
- Chromosomal
- What makes them environmentally hardy?
- What is their relationship with air?
- What are their three important structural components?
- Are they pathogenic in guinea pigs?
- Resistant to acid and alkali - they have to survive outside of the human body, they are transferred in the air
- Obligate aerobe - unusual for a pathogen, M. tuberculosis is restricted to oxygenated parts of the body
- 1- Mycolic acids (acid fastness), 2- Phosphatides (ceseation necrosis) 3- cord factor (trehalose dimycolate): virulence, microscopic serpentine appearance
- Yes
- How is M. tuberculosis transmitted?
- How many organisms do you need to initiate infection?
- What happens when the bacteria land on the lung?
- What happens with immunocompetent persons?
- inhalation of infected aerosols
2.
M. tuberculosis pathogenesis is a cell mediated immune response 2-3 weeks after initial infection. Name the two parts:
- CD4 helper T cells activate infected macrophages to kill intracellular bacteria
- CD8 suppressor T cells lyse other infected macrophages -> caseating granulomas (‘tubercules”) - gradular necrosis in the tissues - mycobacteria cannot continue to grow within these granulomas, so the infectious process pauses (latency)
TNF plays an important role in maintaining latency; Patients receiving TNF-alpha antagonists (Remicade) may reactivate TB
When TB infects the lungs, how does it spread to the bloodstream?
Bacilli proliferate locally and spread through the lymphatics to a hilar node, forming the Ghon complex (exudative lesion plus hilar node), launch from the Gohn complex to the bloodstream (bacteremia and hematogenous spread) -> miliary TB (loci of TB replication) -> potentially TB meningitis
TB granulomas are found there there is a high partial pressure of O2
With latency, you get calcified TB granulomas - can get reactivation of TB
What are some risk factors for infection?
What are some risk factors for poor outcome?
- crowded (prisons, hospitals, homeless shelters)
- HIV
- Uncontrolled HIV (inadquate highly active antiretroviral therapy)
- Steroids
- INF gamma deficiency
- TNF-alpha antagonist (Remicade)
- Age < 5 yrs
What does a classic active pulmonary TB present with?
cough, weight loss (consumption), fever, night sweats, hemoptysis (spitting up blood) and chest pain
Chest radiograph, cavity formation indicates advanced infection, associated with hgh bacterial load
noncalcified round infiltrated - may be confused with lung carcinoma
- What is TB scrofula?
2. What is the trend of mycobacterial cervical infections in adults v. peds?
1.Reactivation in lymph node
A painless enlarging persistent mass. Cervical lymph node is affected in 2/3. Systemic symptoms include fevel/chills, weight loss, or malaise
2. In adults caused by M. tuberculosis, in peds caused by atypical mycobacterium (contaminted objects in their mouths)
- What is the most common site for extrapulmonary infection?
- Genitourinary TB - TB almost always reaches the kidneys during the primary infection but does not present clinically; may be 20 yrs of latency before symptoms; usually secondary to renal tuberculosis
What are the main manifestations of skeletal TB?
- Arthritis of one joint
2. Pott disease (spinal infection); back pain, stiffness, paralysis of lower extremeties
What is the name of the hematogenous spread of TB throughout the body that looks like “millet seeds” in lungs on chest X ray?
Miliary Tb; more likely to develop right after primary infection, less likely as reactivation, highest risk in very young and old, fatal if untreated
What is something strange that manifests in TB meningitis in children?
Brudzinski Neck Sign
You see strange neurological signs i.e., you lift head and knees lift up
Develops in 5-10% of children younger than 2
