Summary of Tests for Identification
of Staphylococci
Clinical Microbiology Review 160
TEST PRINCIPLE KEY REACTIONS OTHER
Catalase
Coagulase
Slide agglutination tests
for S. aureus
Mannitol salt agar (MSA)
Novobiocin susceptibility
Bubbles after 20–30 sec aren’t
considered pos rxn. Catalase from
RBCs in blood agar may produce
weak bubbles.
Slide test is screening test. Detects
bound coagulase (clumping factor).
If neg, tube test should be performed.
Detects free coagulase. Largely re-
placed by latex agglutination tests.
Most labs report pos organisms as
S. aureus.
7.5% salt inhibits most organisms
other than staph. All staph can
grow on MSA. Rarely used for ID of
S. aureustoday because other
species ferment mannitol.
Performed on CNS isolated from
urine.
Enzyme catalase converts 3%
hydrogen peroxide (H 2 O 2 ) to
oxygen & water. Immediate
bubbling.
Enzyme coagulase causes coagula-
tion (tube test) or agglutination
(slide test) in plasma.
Agglutination of latex beads coated
with fibrinogen & abs to protein A
(protein in cell wall of S. aureus).
Fermentation of mannitol results in
color change from pink to yellow.
Organisms resistant to novobiocin
grow to edge of disk.
Staphylococci pos. Strepto-
cocci & enterococci neg
S. aureuspos
S. aureuspos
S. aureuspos
S. saprophyticusis resistant.
Other CNS susceptible
