Tuberculosis (3) Flashcards
T/F: mycobacteria gram stain well
False…they gram stain poorly because of the mycolic acid in the peptidoglycan cell wall
Describe the process of gram staining:
1- Cover smear w/ carbofuchsin, steam over boiling water for 8 minutes
2- After slide has cooled, decolorize with acid- alcohol for 15-20 minutes
3- Counterstain with methylene blue for 30s
4- Rinse briefly with water to remobe excess methylene blue
5- Blot dry with bibulous paper and examine
Do M. tuberculosis grow in vitro?
Yes, but very slowly
Describe the important structural component of M. tuberculosis?
1- mycolic acid (gives it the acid fastness
2- Wax D (ajuvant)
3- Phosphatides (caseation necrosis)
4- Cord factor (virulence, microscopic serpentine appearance)
5- Phtiocerol dimycocerosaete (lung pathogenesis)
What is the natural host and reservoir for M. tuberculosis?
Humans
They are also pathogenic in guinea pigs
T/F: M. tuberculosis are intra- or extracellular obligate aerobes
True
How does M. tuberclosis keep its Ab resistance genes… on plasmid or chromosomes?
Chromosomes
What is the infectious dose of M. tuberclosis?
<10 organisms can initiate infection…it is extremely infectious
Describe the pathogenesis of tuberclosis?
1- Alveolar macrophages phagocytose the inhaled bacilli
2- Naive macrophages are unable to kill the intracelluar mycobacteria and the bacteria proliferate in the phagocytes and travel to extrapulmonary sites
What are the main sites that TB establises latency or active extrapulmary infections?
Lymph nodes
Kidney
Bones
Meninges
How is the GI infected with TB?
Swallowing infectious sputum
What type of immunity is needed for TB infections?
Cell Mediated immunity…it terminates the unimpeded growth of M. tuberclosis 2-3 weeks after initial infection
What cytokine helps maintain TB latency?
TNF
What is a Ghon complex?
Exudative lesion plus draining lymph nodes…they are usually found in the lower lobes of the lungs
What are granulomatous lesions?
Central area of infected Langhans giant cells surrounded by a zone of epitheloid cells
What is a tubercule?
Older granuloma surrounded by fibrous tissue, central caseation necrosis, heals by fibrosis and calcification
What are the symptoms of classic active pulmonary TB?
Cough, weight loss, fever, night sweats, hemostysis, chest pain
What does a CXR for active pulmonary TB show?
Cavity formation (indicates advanced infection and is associated with a high bacterial load
Noncalcified round infiltrates
Symptoms of TB scrofula?
Cervical adenitis, usually unilateral
more commonly caused by TB in adults, not pediatric cases
How is TB scrofula treated?
surgery
Symptoms of GU TB?
Dysuria, hematuria, flank pain, “sterile pyuria”
Genital is usually secondary to renal
Most common site for extrapulmonary infection
What are the symptoms of CNS TB?
CSF: decreased glucose, increased protein, pleocytosis
MRI is needed for Dx
Symptoms of skeletal TB?
Arthritis in 1 joint
OR
Pott disease (spinal infection)–> back pain, stiffness, paralysis or lower extremities
Symptoms of GI TB?
Abd pain, weight loss, anemia, fever w/ night sweats, obstruction and palpable mass
Symptoms of milliary TB?
Many tiny noncalcified foci or infection
Who is at greatest risk for milliary TB?
65 yo individuals with a primary infection
What are the symptoms of TB meningitis?
+ brudzinski sign, nuchal rigidity, lethargy, cranial nerve palsies, altered DTRs
Who is at greatest risk of TB meningitis?
Children <2 yo
How is a PPD interpreted?
15mm= positive
10mm= positive if patient has risk factors
5mm= positive if has deficient CMI
When will a PPD read positive if infected?
2-10 weeks after infection
Can TB be cultured?
Yes, but grows very slowly….can take up to 2 weeks
What are some Lab tests for the Dx of TB?
PCR for bacterial rRNA DNA (fast but not very sensitive)
Quanifuron gold–> TB blood tests detects latent infections and is specific for TB
How is pumonary TB treated?
At least 6 months of isoniazid and rifampin and 2 months of pyrazinamide
How are immunocompromised, disseminated disease and likely drug resistant cases treated?
9-12 months of:
Isoniazid, rifampin, pyrazinmide, ethambutol
How are asymptomatic or latent infections treated?
6 months of isoniazid
How are pediatric exposure treated?
6 months of prophylactic isoniazid
How are MDR strains treated?
Cipro, amikacin ethionamide and cycloserine
How are XDR strains treated?
CDC must be called for information
Is there a TB vaccine?
Yes…the BCG vaccine (“bacillus calmette-Guerin”)
It prevents 7-% of symptomatic infections but does not prevent latent infections
