Staphylococcus practical عملي

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 50 % produce lemon yellow color

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

Staphylococcus

Catalase NEG

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. aureus

Coagulase NEG

Coagulase POS

Staphylococcus aureus

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.