lab diagnosis of Staphylococcus aureus

1. Staphylococcus aureus
Prepared by
Samira Fattah
Assis. Lec.
College of health sciences-HMU
Lab 2

2. • The Staphylococcus genus includes at least 40 species.
• The three main species of clinically importance are:
• S. aureus:
pathogenic and commensally found in nose (nares).
• S. epidermidis:
is a commensal of the skin, but can cause severe infections
in immune-suppressed patients.
• S. saprophyticus:
is part of the normal vaginal flora, is predominantly implicated
in genitourinary tract infections.

3. LABORATORY DIAGNOSIS:
Specimen collection
• Pus from pyogenic lesions.
• blood from septicaemia.
• Cerebrospinal fluid from meningitis.
• sputum from respiratory infection
• suspected food, vomit or faeces from food poisoning.
• Mid-stream urine in urinary tract infection.
• Anterior nasal swab from suspected carriers.

4. microscopic examination
1-Gram stain gram positive.
2-Morphology cocci (spherical).
3-Arrengment single cell or pairs or in short chain
but appear predominantly in grape-like clusters.

5. culture characteristic
colony morphology on many types of agars:
-On nutrient agar
Staphylococcus aureus
colonies are:
large, circular, smooth ,
shiny surface and are
pigmented (golden-yellow).

6. -On blood agar
• S. aureus
β-hemolysis /clear zone around the colonies.

7. • S.epidermidis
-White-creamy colonies
-no hemolysis of red blood cells.

8. • S. Saprophyticus
- white-yellow colony
-no haemolysis of red blood cells

9. -On mannitol salt agar
- It is a differential medium for
mannitol fermentors.
-The media contain mannitol and the
indicator phenol red and 7- 10% sodium
chlorid.
-Staphylococcus aureus produce yellow
colonies with yellow zones(mannitol
fermentor).
-Other Staphylococci produce small pink or
red colonies with no colour change to the
medium(non-mannitol fermentor)

11. Biochemical tests
- Catalase test:
• Is used to differentiate between staphylococci
(catalase +ve) and streptococci(catalase –ve).

12. -DNase TEST
•Deoxyribonucleic Acid enables
the detection of DNase that
depolymerize DNA.
•A zone of clearing around the
spot or streak indicates DNase
activity.

13. -Coagulase test
is used to differentiate Staphylococcus aureus from
coagulase-negative staphylococci.
fibrinogen fibrin
(clot formation)
coagulase

14. slide coagulase test
• Procedure
– Place a drop of sterile water
on a slide and emulsify a
colony
– Add a drop of rabbit plasma
to the suspension
– Observe
• Agglutination = Positive
(S. aureus)
• No agglutination=
Negative (other
staphylococcci)
tube Coagulase Test
• Causes a clot to form when
bacterial cells are incubated with
plasma.
• Procedure
• Inoculate rabbit plasma with organism
and incubate at 35-37 0 C
• Observe at 30 minutes for the
presence of a clot
• Continue for up to 24 hours, if
needed.

15. -Novobiocin Susceptibility Test
• This test is used to differentiate coagulase-negative
staphylococci.
Staphylococcus saprophyticus Staphylococcus epidermidis

16. API Test
-API STAPH
Combination of standard biochemical tests and fermentation
tests which are the reference tests for the identification of
staphylococci.

17. Rapid diagnostic tests
• This techniques include Real-time PCR which is increasingly
being employed in clinical laboratories.