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.
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)
10.
11. Biochemical tests
- Catalase test:
⢠Is used to differentiate between staphylococci
(catalase +ve) and streptococci(catalase âve).
12. -DNase TEST
â˘Deoxyribonucleic Acid enables
the detection of DNase that
depolymerize DNA.
â˘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
â Place a drop of sterile water
on a slide and emulsify a
colony
â Add a drop of rabbit plasma
to the suspension
â 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.