Gram Positive Biochemical Testing

How do we biochemically identify gram positive bacteria?
- gram stain
- bacterial size, shape, arrangement
- spores
- catalase test
- coagulase test
What are the two tests we do for biochemically testing for gram positives?
- catalase test
- coagulase test
What does the catalase test distinguish between?
- Staphylococcus - positive
- Streptococcus - negative
What does the catalase act on?

hydrogen peroxide
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
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
Which bacteria do we perform the coagulase test on?

Staphylococcus
What does the coagulase test coagulate?

coagulates plasma
What is the defense mechanism for pathogenic Staphylococcus?

coat themselves with host fibrin to escape host immune system
Which Staphylococcus is positive with the coagulase test?
- S. aureus
- S. intermedius
Which Staphylococcus is negative with the coagulase test?
- S. epidermidis
- S. saprophyticus
What are the two types of coagulase tests?
- tube test
- slide test
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
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

Author

kris10leejmu

196482

Card Set

Gram Positive Biochemical Testing

Description

Microbiology Three

Updated

2013-01-30T04:09:19Z

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