Diagnosis of Staphylococcus aureus
Identification of Staphylococcus aureus
B- swabs from infected sites
D- cerebrospinal fluid
E- blood for culture.
F- Faeces when foodpoisoning is suspected.
Staphylococci are Gram positive cocci graplike clusters also sometimes singly and in pairs They are non-motile and non-capsulate.
*Most Staphylococci grow well aerobically and few strains grow anaerobically
-Temperature range for growth is 10–42 ºC, with an optimum of 35–37C.
A- Blood agar, chocolate (heated blood)agar:
-S. aureus produces yellow to cream colonies after overnight incubation
-Some strains are beta hemolytic when grown aerobically.
-Colonies are slightly raised.
B- MacConkey agar:
-Smaller colonies are produced after overnight incubation at 35–37 ºC.
-Most strains are lactose fermenting.
C- Mannitol salt agar:
-A useful selective medium for isolating S. aureus from faecal specimens when investigating staphylococcal food-poisoning.
-It can also be used to screen for nasal carriers.
-S. aureus ferments mannitol and is able to grow on agar containing 70–100g/l sodium chloride.
-Mannitol salt agar cont aining 75 g/l sodium chloride .
S. aureus is:
Catalase positive .
S.epidermidis ————– Susceptible for Novobiocin
S. saprophyticus —————– Resistant for Novobiocin