This document discusses Staphylococcus aureus and methods for its laboratory diagnosis. It notes that S. aureus is commonly found in the nose and can cause infections, while S. epidermidis lives on the skin and S. saprophyticus in the vagina. Diagnosis involves collecting samples from infections and using gram staining, culturing, and biochemical tests like catalase, coagulase and novobiocin to identify the species. Rapid PCR tests are also now used to diagnose S. 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.