Bacterial Pneumonia 2 Flashcards
legionella bacteriology
gram (-) rods. stains poorly by gram stain or H&E (use silver or IF). facultative intracellular parasites. free-living form is motile (flagella). intracellular form is non-motile. reservoirs are in freshwater protozoa and biofilms in commercial water systems. humans are unnatural “dead end” host for legionella
legionella replication
begins living in biofilm in warm water or soil. taken up by phagocytosis. contained in an altered phagosome that doesn’t get merged to a lysosome. becomes motile and escapes the phagosome. lyses cell and spreads to another cell.
3 outcomes of legionella infection in humans
asymptomatic seroconversion. pontiac fever (flu like, resolves without complication). legionnaires disease (pneumonia. suppression of kidney function. usually resolves with hospitalization and treatment. can be fatal)
risk factors for legionnaires disease
increasing age. immunosuppression. smoking. chronic heart or lung disease. chronic swallowing disorder. being male. for outbreaks, treavel is common: conventions/weddings at a hotel.
legionnaires occurrence and mortality
80% of cases are isolated. 20% present as members of an outbreak. reportable. outbreaks are a simultaneously exposed group, not contagious. mortality decreasing due to prompt diagnosis and early use of appropriate antibiotics.
presentation of legionnaires disease
altered mental status. high fever/chills. headache. acute renal failure. pneumonia/cough/chest pain. pancreatitis. diarrhea. need labs to differentiate from other pneumonias.
how to diagnose legionella infection (urine antigen test)
urine antigen test: commercial ELISA test. fast test. reliably detects LP1 strain of L pneumophila, which causes 90% of LD in the USA. testing significantly associated with reduced mortality.
how to diagnose legionella infection (culture)
respiratory secretion culture. slower. technically demanding. detects many strains and species of legionella. 27% fatality rate among culture pos, urine test neg patients.
treatment of legionella infections
pontiac fever often resolves witout treatment. LD requires an antibiotic that penetrates infected cells: levofloxacin, azithromycin, erythromycin.
C. burnetii bacteriology
zoonosis of asymptomatic infection of ruminants. transmitted to humans by inhalation of aerosols of infected ruminant urine, feces, birthing matter (no vector). super infectious. multiplies in aveolar monocytes and macrophaeges and travels in them to liver, spleen, bone marrow. acid phosphatase and superoxide dismutases help survive in fused lysosome/endosome.
C. burnetii pathogenesis/presentation
fever, chills, sweats, headache, dry cough, pneumonia, hepatits, pregnancy issues, rash, endocarditis, rarely fetal, reportable.
C. burnetii diagnosis and treatment
imunohistochemical methods, ELISA, immunofluorescence. use doxycycline or fluoroquinolones to treat. vaccine available to farm and vet personnel and military stationed in the middle east
mycoplasma pneumoniae bacteriology
smallest freeliving organisms. strictly aerobic. no cell wall. only prokaryotic cell membrane that contains cholesterol. difficult to culture. fried egg shaped colonies. only one serotype, but immunity is incomplete
mycoplasma pathogenesis
resides on mucosal surfaces of respiratory and genital tracts. transmitted by inhalation of respiratory aerosols. causes tracheobronchitis, bronchiolitis, 5-10% progresses to atypical walking pneumonia. P1 adhesin binds respiratory epithelial cells. some intracellular penetration. CARDS exotoxin causes ciliostasis and some cell death. local inflammation from bacterial wastes.
mycoplasma and anemia?
antibodies against mycoplasma cross-react with red blood cell membranes (cold agglutinins) so patients may become anemic. resolves spontaneously with disease.
