1. Staphylococci are gram-positive cocci that grow in clusters and are catalase-positive. The coagulase test is used to differentiate Staphylococcus aureus from coagulase-negative staphylococci (CoNS). 2. S. aureus causes a variety of diseases including localized skin infections, pneumonia, bacteremia, osteomyelitis, endocarditis and toxic shock syndrome. Identification involves culture, microscopy, and biochemical tests like coagulase and catalase. 3. Strain typing methods are used to trace outbreak sources and identify toxin-producing strains causing food poisoning and toxic shock syndrome.

1. Staphylococci

2. Morphology
Gram positive cocci
in clusters

3. Catalase: +ve
(streptococci catalase –ve)
:Coagulase
ve: S. aureus+
ve: CoNS-

4. Coagulase Test
:Principle
Fibrinogen
Plasma
Coagulase enzyme
Fibrin
Visible Clot
Broth
:Procedure
culture
2
(organism)
1 ml dil. citrated plasma 1
3 Incubate at 37oC, observe for formation of
visible clot.

5. S.aureus
((coagulase +ve staphylococci

6. Morphology
Gram positive cocci
in clusters

7. Culture
(Nutrient agar (golden yellow endopigment

8. (Blood agar (ß-haemolysis

9. (Mannitol-Salt agar (MSA
• Selective, differential medium.
• 7.5% sodium chloride + mannitol
sugar.
S. aureus (ferment(
• Mannitol
Acid
(yellow(
CoNS (No fermentation(
• Mannitol
No acid
(Red(

10. Virulence Factors for Pyogenic Diseases

11. PYOGENIC DISEASES
A- Localized Skin infections

13. B- Staphylococcal Pneumonia

14. C- Invasive Infections
•
•
•
•
•
Bacteremia.
Osteomyelitis.
Acute bacterial endocarditis.
Meningitis.
Septicemia.

15. Diagnosis of Pyogenic Diseases
:Specimen -1
Abscess ----- pus
Endocarditis ----- blood
Meningitis --- CSF, blood
Pneumonia ----- sputum
UTI ----- urine
Direct detection- 2

16. Culture- 3
Blood
Other than blood
(pus, CSF, urine)
subculture

17. Identification- 4
A- Colony Morphology

18. B- Microscopy

19. C- Biochemical Reactions
Coagulase-1
Catalase-3
Clumping factor-2

20. Toxin-Mediated Diseases
A- SSS
Exfoliatin
B- TSS
TSST-1
C- Food poisoning
Enterotoxins

21. A- Staph. Scalded Skin Syndrome

22. B- Toxic Shock Syndrome
Predisposing factors:
- First observed in Menstruating
females using tampons )tampon
retained in vagina for 4-5 days(
- Any staphylococcal lesion can
predispose to TSS.
Virulence factor: TSST-1
Diagnosis:
clinical picture.
culture: for isolation & identification.
ELISA: for toxin detection in blood

23. C- Staph. aureus food poisoning
I.P:
1- 6 hrs.
Clinical picture:
Colic, vomiting, mild
Diarrhea, but no fever
Diagnosis:
1. Specimen: food, vomitus, stools.
2. Culture: on MSA.
3. ELISA: for toxin detection in sample or in isolated
organism.
4. Strain typing: to trace source of infection )e.g. phage
typing(.

24. Strain Typing
•
•
•
•
•
•
Phage typing.
Colony morphology.
Biotyping.
Plasmid profile.
Ribotyping.
Chromosomal
analysis.

25. Treatment
Penicillin-resistant S.aureus- 1
.MRSA- 2
VISA- 3
VRSA

26. Coagulase negative Staphylococci (CoNS)
• General Characters:
– Non-hemolytic on blood
agar
– Coagulase negative
– Mannitol non-fermenter
• Diseases:
S. epidermidis:
– Device-related infections
(prosthetic valve
endocarditis, shunt
infections, … etc…)
– Urinary tract infection
– Wound infection
S. saprophyticus:
UTI (honeymoon) cystitis

27. Case 1
A man underwent an emergency operation for
perforated appendix. He required admission
to the Intensive Care Unit. On the 5th day
of hospitalization he developed fever, and
the wound was erythematous, swollen,
with purulent discharge (Surgical site
infection “SSI”). The surgeon requested
bacteriological examination (culture and
sensitivity) of the wound pus

28. Surgical site infection

29. Specimen
• Wound swabs were
obtained.
• Gram staining &
Microscopy
Gram-positive
cocci arranged in
clusters amongst pus
cells.

30. Culture
On Blood agar →
Beta-hemolysis
On nutrient agar →
Golden yellow pigment
On MSA →
Yellow colonies

31. Identification:
Film from colonies
Gram-positive cocci
in clusters

32. Biochemical reactions
Catalase +ve
Coagulase +ve
Clumping
factor +ve

33. Which organism is causing this
condition?
• Gram-positive cocci in clusters, catalase positive
staphylococci
• β-hemolysis , golden yellow pigment, yellow
colonies on MSA and coagulase positivity
S. aureus
.

34. Antimicrobial susceptibility “Disc
diffusion”
the organism is
resistant: to
oxacillin, penicillin,
erythromycin,
& gentamicin
but sensitive to:
vancomycin.

35. How do you interpret the
?susceptibility data
The organism is multi-resistant, including
oxacillin-resistant
methicillin-resistant S. aureus (MRSA).

36. Name other diseases caused by
.this organism
1. Pyogenic infections
a. Localized skin infections, e.g. folliculitis, furuncles,
abscess.
b. Staph pneumonia
c. Invasive staph. infections, e.g. endocarditis, cellulitis,
osteomyelitis, and septic arthritis
2. Toxin-mediated diseases
, a. Toxic shock syndrome
,b. Scalded skin syndrome
c. Food poisoning.

37. Case 2
A group of people shared a carbohydrate- rich
meal. 1-6 hours later, they manifested vomiting,
diarrhea but no fever. The condition was mild and
self- limited.
a) What could be the clinical diagnosis?
b) What is the possible causative organism?
c) What is the virulence factor responsible for this
condition?
d) What is the mechanism of action of such
virulence factor?
e) What is the laboratory test that is used to trace the
source of this outbreak?

38. MCQs

39. 1. All the following are characteristic features
of staphylococci except:
a)
b)
c)
d)
e)
Gram positive cocci.
Arranged in clusters.
Catalase negative .
Usually grow on simple media.
Usually inhabit skin and mucosa.

40. 2. The following medium is used to isolate S.
aureus from specimens contaminated by
other bacteria:
a) Nutrient agar.
b) MacConkey's agar.
c) Blood agar .
d) Mannitol salt agar.
e) Chocolate agar

41. 3. The localized nature of S. aureus lesions is due
to:
a) Adhesins.
b) Protein A.
c) Staphylocoagulase
d) Staphylokinase
e) Exfoliatin

42. 4. S. aureus growth can be identified by the
following characters except:
a) Colony on blood agar is golden yellow.
b) Colony on blood agar is surrounded with a clear
zone.
c) Colony on Mannitol salt agar is rose pink.
d) Protein A positive.
e) Coagulase test positive.

43. 5. One of the following is a S. aureus toxinmediated disease:
a) Folliculitis
b) Staphylococcal pneumonia.
c) Toxic shock syndrome.
d) Osteomyelitis
e) Carbuncles

44. 6. Staphylococcal strain typing is used :
a) To diagnose staphylococcal pyogenic diseases.
b) To differentiate between coagulase -ve and
coagulase +ve staphylococci.
c) To differentiate between staphylococci &
streptococci.
d) To trace the source of outbreaks of S. aureus in
the epidemiological studies.
e) To identify enterotoxin-producing strains of S.
aureus.