Irregular shape
Coagulase:
Coagulase is an enzyme produced by Staphylococcus aureus that
converts fibrinogen to fibrin. In the laboratory, it is used to
distinguish between different types of Staphylococci isolates. Coagulase
negativity excludes S. aureus. S. aureus is
coagulase-positive.
Slide coagulase test: The slide Coagulase test
detects bound coagulase (clumping factor). This type of coagulase is
attached to the bacterial cell walls (surface). This test is usually
performed on a glass slide.
Tube Coagulase test: The coagulase test is used
to differentiate Staphylococcus aureus from coagulase-negative
staphylococci. The test uses rabbit plasma that has been inoculated with
a staphylococcal colony. The tube is then incubated at 37 degrees
Celsius for 1-1/2 hours. If negative, then incubation is continual up to
24 hours. This test detects free coagulase (coagulase that is released
by bacterial cells into culture).
Positive (i.e., the suspect colony is S. aureus). The serum will coagulate, resulting in a clot (sometimes the clot is so pronounced that the liquid will completely solidify)
Negative, the plasma remains liquid. A negative result may be S. epidermidis
If bubbles or froth
forms, the organism is said to be catalase-positive.
Staphylococci and micrococci are catalase-positive
If no bubbles form, the organism is catalase-negative. Streptococci and Enterococci are catalase-negative