Gram Positive Biochemical Testing

  1. How do we biochemically identify gram positive bacteria?
    • gram stain
    • bacterial size, shape, arrangement
    • spores
    • catalase test
    • coagulase test
  2. What are the two tests we do for biochemically testing for gram positives?
    • catalase test
    • coagulase test
  3. What does the catalase test distinguish between?
    • Staphylococcus - positive
    • Streptococcus - negative
  4. What does the catalase act on?
    hydrogen peroxide
  5. How do we do the catalase test?
    • take a small colony from the agar
    • place on microscope slide
    • add a drop of catalase reagent (3% hydrogen peroxide)
    • gas bubbles - positive
    • no gas bubbles - negative
  6. What do we need to be careful to avoid when do the catalase test?
    • avoid blood agar or be careful not to transfer any blood agar to the slide
    • blood will cause hydrogen peroxide to fizz even with a negative result
  7. Which bacteria do we perform the coagulase test on?
  8. What does the coagulase test coagulate?
    coagulates plasma
  9. What is the defense mechanism for pathogenic Staphylococcus?
    coat themselves with host fibrin to escape host immune system
  10. Which Staphylococcus is positive with the coagulase test?
    • S. aureus
    • S. intermedius
  11. Which Staphylococcus is negative with the coagulase test?
    • S. epidermidis
    • S. saprophyticus
  12. What are the two types of coagulase tests?
    • tube test
    • slide test
  13. How do we do the tube coagulase test?
    • in a test tube, inoculate 0.5 ml of rabbit plasma with a loop full of organisms from a non-inhibiting media (blood agar)
    • incubate
    • read hourly for 4 hours
    • negative - no clot formation¬†
    • positive - clot formation
  14. How do we do the coagulase slide test?
    • take a loop full of organisms from a colony
    • emulsify in a drop of water or saline solution
    • make a thick suspension
    • add a drop of rabbit plasma
    • stir with sterile loop
    • positive - clumps within 5 - 20 seconds
Card Set
Gram Positive Biochemical Testing
Microbiology Three