Mycobacteria: TB, Lepros, and Atypicals Flashcards
m. tuberculosis bacteriology
gram stain poorly, but are almost uniquely acid fast. grows slowly in vitro. humans are natural host and reservoir. can be intra or extracellular. produce no toxins. drug resistance is chromosomal. environmentally hardy. obligate aerobe.
important structural components of m. tuberculosis
mycolic acids: acid fastness
wax D: adjuvant
Phosphatides: caseation necrosis
cord factor: virulence and serpentine appearance
phtiocerol dimycocerosate: lung pathogenesis
m. tuberculosis pathogenesis
transmitted by inhalation of infected aerosols mainly.
ghon complex
parenchymal focus and hilar lymph node lesions. forms when bacilli proliferate and spread through the lymphatics to a hilar node. exudative lesion
proliferative lesions vs. exudative lesions in TB
prolif develop where bacillary load is small and host cellular immune responses dominate. exudative lesions predominate when large numbers of bacilli are present and host defenses are weak. these loose aggregates of immature macrophages, neutrophils, fibrin, and caseation necrosis are sites of mycobacterial growth
risk factors for m. tuberculosis infection
crowded at-risk environments like prisons, homeless shelters, hospitals. HIV. immunosuppressed.
m. tuberculosis diagnosis: exam
classic pulmonary TB = cough, weight loss, night sweats, fever, hemoptysis. Chest xray shows cavity formation, noncalcified round infiltrates. fiberoptic bronchoscopy most effective way to get cultures. nonpulmonary symptoms mimic a wide variety of diseases.
TB scrfula
reactivation in lymph node. painless, enlarging, or persistent mass. symptoms: fever, weight loss, malaise. cervical lymph node affected in 2/3. mostly caused by m. tuberculosis in adults, but usually caused by atypicals in kids. do PPD and fine needle aspiration. surgery only after antibiotic treatment is well underway
genitourinary TB
most common site for extrapulmonary infection. TB almost always reaches kidney during primary infection but usually doesnt present clinically. females present with infertility, menstrual disorders, pain. pregnancy rare, but leads to spont. abortion or ectopic preg. IV urography best option. can use CT, MRI, ultrasound. needs surgery.
CNS tuberculosis
visualize by MRI with gadolinium. CSF analysis used to detect decreased glucose, elevated protein, slight pleocytosis. PCR assays can be used.
skeletal TB
shows up as arthritis of one joint or pott disease (back pain, stiffness, paralysis of lower extremities)
GI TB
abdominal pain, weight loss, anemia, fever with night sweats, obstruction, palpable mass. radiograph for calcified granulomas. mesenteric lymphadenopathy. use exploratory surgery
miliary TB
hematogenous spread through body, many tiny noncalcified foci of infection appear like millet seeds. more likely to develop right after primary infection. highest risk in young and old. history of cough/respiratory distress. lymphadenopathy and hepatosplenomegaly. tachypnea. cyanosis. lesions on skin or choroidal tubercles in retina. tiny nodules best visualized by chest xray with bright spotlight.
TB meningitis
nuchal rigidity. altered deep tendon reflexes. lethargy. cranial nerve palsy.
pediatric TB
middle ear, skin, ocular structures. rule out TB if presents with pneumonia, pleural effusion, cavitary mass lesion in lung. gastric aspirates are used in lieu of sputum in kids younger than 6. begin treatment as soon as samples have been taken for culture. pediatric TB can be lethal before TST is positive