عاجل

Diagnosis of Staphylococcus aureus

Identification of Staphylococcus aureus


LABORATORY FEATURES

Specimens:

A- Pus

B- swabs from infected sites

C- sputum

D- cerebrospinal fluid

E- blood for culture.

F- Faeces when foodpoisoning is suspected.


Microscopic examination

Staphylococci are Gram positive cocci graplike clusters also sometimes singly and in pairs They are non-motile and non-capsulate.


Culture

*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 .


Biochemical tests

S. aureus is:

Catalase positive .

  • Coagulase positive.

  • DNase positive.

  • Novobiocin

S.epidermidis ————– Susceptible for Novobiocin

S. saprophyticus —————– Resistant for Novobiocin

حول: هلال سود
تعليقات ( 120 )
دخول

تسجيل

نحن نأسف فالتسجيل مغلق حاليا , تواصل بالإدارة للقيام بهذه الوضيفة