Gram-Positive Rods-Felton Flashcards
What are the general characteristics of Corynebacteria?
- Gram-positive rods, non-sporeforming, obligate aerobes
- slender, with club-shaped swellings at ends
- No flagella or capsule
- Stain irregularly due to metachromatic granules (polyphosphate)
- Cell wall contains mycolic acids (long-chain branched fatty acids) similar to (but smaller than) those present in Mycobacteria.
- Not acid-fast.
What is the distribution of Corynebacteria?
- Soil and on humans and animals.
* Diptheroids are found in: human nose, throat, conjunctiva and on skin.
What are the characteristics of the exotoxin of Corynebacterium diptheria?
- Protein exotoxin (diphtheria toxin) which is the key virulence factor.
- The toxin gene is located on a phage genome.
- Heat-labile secreted protein.
How is the exotoxin of Corynebacterium diptheria activated? Which fragment is enzymatically active?
- Converted to active toxin by proteolytic cleavage of peptide bond between amino acids 194-195. This divides it into two fragments, A and B, which remain attached to each other by disulfide linkages.
- . Fragment A is the enzymatically active (toxic) portion of diphtheria toxin. It is an ADP ribosyltransferase, like exotoxin A of Pseudomonas. It transfers the ADP-ribose portion of NAD to protein synthesis elongation factor EF2, and thus irreversibly inhibits protein synthesis and kills the cell.
- Fragment B is required for binding of diphtheria toxin to its receptor on the cell surface and for translocation of the A fragment across the membrane into the cytoplasm of the target cell.
What level of the exotoxin of Corynebacterium diptheria is toxic? What regulates the synthesis of diptheria toxin? What is toxoid?
- Diphtheria toxin is lethal at 0.1 ug/kg in rabbit and guinea pig. Only 1/10,000 ug is sufficient to produce a skin reaction in humans. One molecule will kill one cell by inhibiting protein synthesis within a few hours.
- Synthesis of diphtheria toxin is regulated by the concentration of iron. High iron concentration represses production of diphtheria toxin, and limiting iron concentration turns it on.
- Diphtheria toxin can be converted to toxoid by treatment with formalin at 37 degrees C. Toxoid is immunogenic but non-toxic and is used as a vaccine, since almost all the pathogenesis by C. diphtheriae is due to its toxin.
What is the pathogenesis of Corynebacterium diptheria infection?
- Spread by aerosols and respiratory droplets.
- Begins in upper respiratory tract and multiplies in throat mucosa.
- Toxin kills neighboring cells, causing inflammation, enlargement of lymph nodes, moderate fever, cardiac, neurologic and renal complications.
- Schick test used to assess immune status. Inject small amount of diphtheria toxin w/ toxoid. Not used anymore.
What are the lab diagnostics for Corynebacterium diptheria infection?
- Nose and throat swabs.
- Gram or methylene blue stains.
- Elek immunodiffusion test:
oFilter paper strip saturated w/ antitoxin put on agar plate.
oStreak the plate with suspected culture in a line perpendicular to the strip.
oToxigenic strain will produce a precipitin line composed of toxin-antitoxin immune complexes at 45 degree angle between filter paper strip and line of growth.
What is the treatment for Corynebacterium diptheria infection? What can be used as prevention?
Treatment: Antitoxin therapy w/o delay.
•Antibiotic therapy in addition.
Prevention: Immunization w/ diphtheria toxoid (DaPT vaccine)
What are the general characteristics of Listeria monocytogenes?
- Opportunistic pathogen.
- Short Gram-positive rod, occurs in pairs or chains
- Tumbling end-over-end motility (at 22 degrees C, but not at 37degrees)
- Attaches to and enters intestinal epithelial cells by binding of a listerial adhesin (called internalin) to an epithelial receptor (called E-cadherin).
- Grows intracellularly in monocytes and macrophages; forms actin “comets”; thus pushed directly from cell to cell.
- Facultative; grows best in 5-10% carbon dioxide.
- Non-sporeforming; no capsule
- Most strains produce weak beta hemolysis on blood agar due to action of listeriolysin.
What is the distribution of Listeria monocytogenes?
- Found in soil and animals
* Contaminates food like ground and processed meat products and milk and cheese.
What are the infection characteristics of Listeria monocytogenes in babies (Perinatal listeriosis)?
Early onset: Sepsis and death before or after delivery.
Late onset: Meningitis (between birth and 3 weeks); high mortality; third most frequent cause of neonatal bacterial meningitis.
What are the infection characteristics of Listeria monocytogenes in adults (Adult Listeriosis)?
Occurs mainly in immunocompromised hosts and pregnant women.
- Meningoencephalitis
- Bacteremia/Septicemia
- Association of infection with various foods (e.g. unpasteurized milk or cheese) indicates that infection is via gastrointestinal tract.
- In some pregnant women or in otherwise healthy people Listeria can occasionally cause acute, self-limited febrile gastroenteritis in foodborne outbreaks with flu-like symptoms, especially following ingestion of a large inoculum, but with smaller inocula asymptomatic carriage is more common.
What are the lab diagnostics for Listeria monocytogenes?
- Isolate from blood or CSF.
- Shows small zone of hemolysis on blood agar.
- Shows that tumbling motility at 22 degrees C.
What are the general characteristics of Erysipelothrix rhusiopathiae?
- Non-motile.
- Microaerophilic
- Smooth form: growth in short chains.
- Rough form: long filaments predominate.
What are the distribution characteristics of Erysipelothrix rhusiopathiae? Infection characteristics? Symptoms? Lab diagnostics?
- Distribution: In animals worldwide but mostly swine.
- Infection: Usually limited to skin.
•Acquired thru skin lesions thru contact w/ fish, shellfish, meat or poultry. - Symptoms:Pain, pruritis, edema, purplish erythematous lesions w/ sharp margins that extend peripherally but are clear centrally. No fever.
- Lab diagnosis:
•Isolate from biopsy of skin lesion on blood agar.
•Weakly hemolytic and resistant to neomycin.
