Transcript Staphylococcus aureus

Staphylococcus
• Family micrococcaeceae
• Genus Staphylococcus
• 3 important species
• 1. Staphylococcus auerus (Coagulase
positive )
•
2. Staphylococcus epidermidis
CoNS
•
3. Staphylococcus saprophyticus
(coagulase negative)
Microscopical appearance
• Gram positive cocci , 1 μm in diameter.
arranged clusters (grape like), tetrads, pairs,
short chains, non motile, non spore forming
mo
• o.
Culture characteristics
• Staphylococci grow readily on most bacteriologic
media under aerobic or faculatively anaerobic
conditions.
• They grow most rapidly at 37 °C but form
pigment best at room temperature (20–25 °C).
• Colonies on solid media are round, smooth,
raised, and glistening.
• Staph aureus usually forms gray to deep golden
yellow colonies.
• Staph epidermidis colonies usually are gray to
white
On nutrient agar
• Staph auerus form golden yellow colonies .
Staph epidermidis
white colonies
on nutrient agar
Staph saprophyticus
lemon yellow color
50 % produce
On blood agar
• Staph auerus
produce complete
haemolysis (clear zone around the growth)
• Staph epidermidis
• Staph saprophyticus
non-haemolytic
(no change on
blood agar)
Staph aureus on blood agar
Biochemical activities
• Catalase test : all spp of Staphyloccoci give
positive catalase which differentiate it from
Streptococci (catalase negative).
H2O2
catalase
H2O + O2
Catalase POS
Catalase NEG
Staphylococcus
Coagulase test
• The coagulase test has traditionally been used
to differentiate Staphylococcu auerus from
coagulase-negative staphylococci . S.aureus
produces two forms of coagulase (i.e., bound
coagulase and free coagulase). Bound
coagulase, otherwise known as "clumping
factor", can be detected by carrying out a slide
coagulase test, and free coagulase can be
detected using a tube coagulase test.
Slide coagulase (Bound) causes bacterial cells to
agglutinate in the plasma
Free coagulase (tube)
active enzyme produced
by S aureus
Fibrinogen  Fibrin
S.
aure
us
Staphylococcus aureus
Coagulase NEG
Coagulase POS
Growth on mannitol salt agar and
mannitol fermentation
• MSA is a selective and differential medium in microbiology
It encourages the growth of a group of certain bacteria
while inhibiting the growth of others. It contains a high
concentration (7.5%-10%) of salt (NaCl), making it selective
for gram positive bacterium Staphylococci since this level
of NaCl is inhibitory to most other bacteria.
• It is also a differential medium for mannitol-fermenting
staphylococci, containing carbohydrate mannitol and the
indicator phenol red a pH indicator for detecting acid
produced by mannitol-fermenting Staphylococci.
Staphylococcus aureus produce yellow colonies with yellow
zones, whereas other Staphylococci produce small pink or
red colonies with no colour change to the medium.