corynebacterium and listeria Flashcards
corynebacterium diptheriae epidemiology
humans are the only known reservoir; the bacteria are carried in the oropharynx or on the surface of the skin; spread person-to-person by inhalation of respiratory droplets containing the bacteria or direct skin contact
c. diptheriae virulence factor
diptheria toxin: A-B exotoxin; inhibits protein synthesis in its target host cells
diptheria toxin
encoded by the tox gene; thsi gene was introduced into C. diptheria by a lysogenic bacteriophage (a virus that infects bacteria)
c. diphtheriae pathogenesis
the bacteria are spread by inhaling respiratory droplets containing the bacteria (usually created by coughing or sneezing); bacteria infect the nose and throat; very rarely the bacteria can be spread from the discharge of skin lesions of an infected person; the diphtheria toxin is produced at the site of infection and then disseminates through the blood to produce the systemic signs of diphtheria; the bacteria do not necessarily enter the blood; the toxin does; the toxin receptor is present on the surface of many eukaryotic cells, particularly heart and nerve cells (explains cardiac and neurological symptoms of sever diphtheria)
c. diphtheriae disease
the clinical presentation of the disease is determined by the site of infection; the immune status of the patient; the virulence of the organism (is the lysogenic prophage and therefore the exotoxin gene present in its genome)
respiratory diphtheria
bacteria multiply locally on epithelial cells in the pharynx or adjacent surfaces; causes localized damage as a result of exotoxin activity; psuedomembrane develops; is firmly attached to the tissue ; systemic complications with severe disease occur when the toxin gains access to the bloodstream and typically involve the heart and nervous system
cutaneous diphtheria
acquired through skin contact with an infected person; the bacteria colonize the skin and gain entry to the subcutaneous tissue through breaks in the skin; a chronic, non-healing ulcer develops; sometimes covered in a grayish membrane
listeria monocytogenes
capable of growth at a broad temperature range (1-45 degrees C) and in a high concentration of salt
listeria epidemiology
disease is generally assoicated with consumption of contaminated food products; transplacentral spread can occur between mother and neonate; fod with small numbers of organisms can become grossly contaminated during prolonged refrigeration
listeria monocytogenes virulence factors
phospholipases and listeriolysisn O - release the bacteria from the phagosome into the host cytosol where they will multiply
ActA - A protein that localizes to one end of the bacterial cell surface and coordinates the assembly of host actin; the provides intracellular motility as the bacteria are pushed towards the cell membrane and into adjacent host cells - spreading infection
listeria monocytogenes pathogenesis
the bacteria adhere to host cells; initially to M cells in the Peyer’s patches of the small inestine; after penetration into the host cells, listeriolysin O and 2 phospholipase C enzymes disrupt the phagosome, releasing the bacteria into the cytosol of the host cell
bacteria replicate within the cytosol and create a polyerizing actin tail (due to ActA) that pushes them through the host plasma membrane into the next cell; since the bacteria are primarily intracellular, humoral immunity has little effect on clearance though cellular immunity is crucial
listeria monocytogenes neonatal disease
early-onset -acquired transplacentally in utero and is characterized by disseminated abscesses and granulomas in multiple organs; late-onset - acquired soon after birth and presents as miningitis or meninogoencephalitis with septicemia
listeria monocytogenes disease in healthy adults
most infecitons are asymptomatic or present as an influenze-like illness; gastroenteritis may or may not occur; disease in pregnant women or patients with cell-mediated immune defects; may present as a primary bacteremia; may present as disseminated disease with hypotension and meningitis
