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Staphylococci

1. Staphylococci

Staphylococci are gram positive cocci, occur in grape like clusters,

In Greek; staphyle – Bunch of grapes Kokkus - Berry

2. CLASSIFICATION:

Based on coagulase production:

1. Coagulase positive: Eg - S. Aureus

2. Coagulase negative: Eg - S. Epidermidis S. Saprophyticus Staphylococcus aureus

MORPHOLOGY:

These are spherical cocci.

Approximately 1µm in diameter.

Arranged characteristically in grape like clusters.

They are non motile and non sporing .

A few strains possess capsules.

3. CULTURE:

Media used :- i ) Non selective media: Nutrient agar, Blood agar, MacConkey’s agar.

Ii) Selective media: Salt-mannitol agar, Paired Barker medium

4. Cultural Characteristics: i ) On nutrient agar- The colonies are large, circular, convex, smooth, shiny, opaque and easily emulsifiable . Most strains produce golden yellow pigments.

5. ii) On MacConkey’s agar- The colonies are small & pink in colour.

Iii) On blood agar- Most strains produce ẞ- haemolytic colonies.

6. Biochemical reactions:

1) Catalase test- Positive. 2) Coagulase test-

1) Slide coagulase test- Positive.

ii) Tube coagulase test- Positive.

7. 3) Reduces nitrate to nitrite.

4) Ferments mannitol anaerobically with acid only.

5) Urea hydrolysis test- Positive.

6) Gelatin liquefaction test- Positive.

7) Produces Lipase.

8) Produces Phosphatase.

9) Produces Thermostable nuclease.

8. PATHOGENICITY:

Source of infection:

A) Exogenous: patients or carriers

B) Endogenous: From colonized site

Mode of transmission:

A) Contact: direct or indirect( through fomites)

B) Inhalation of air borne droplets

9. Virulence factors:

These include

A) Cell associated factors

B) Extracellular factors

10. A) CELL ASSOCIATED FACTORS:

a) Cell associated polymers

b) Cell surface proteins

a) CELL ASSOCIATED POLYMERS

1. Cell wall polysaccharide

2. Teichoic acid

3. Capsular polysaccharide

b) CELL SURFACE PROTEINS:

1. Protein A

2. Clumping factor (bound coagulase)

11. B) EXTRACELLULAR FACTORS

a) Enzymes

b) Toxins

12. a) Enzymes:

1. Free coagulase

2. Catalase

3. Lipase

4. Hyaluronidase 5. DNAase 6. Thermonuclease 7. Staphylokinase ( Fibrinolysin )

8. Phosphatase

13. b) Toxins:

1. Cytolytic toxins i ) Haemolysins

Alpha haemolysin

Beta haemolysin

Gamma haemolysin

Delta haemolysin

ii) Leucocidin (Panton-Valentine toxin)

2. Enterotoxin

3. Toxic shock syndrome toxin (TSST)

4. Exfoliative ( epidermolytic toxin)

14. Disease:

Diseases produced by Staphylococcus aureus is studied under 2 groups:

A) Infections

B) Intoxications

15. A) INFECTIONS:

Mechanism of pathogenesis:

1.Cocci gain access to damaged skin, mucosal or tissue site. ↓

2.Colonize by adhering to cells or extracellular matrix
↓
3.Evade the host defense mechanisms and multiply
↓
4.Cause tissue damage

16. Common Staphylococcal infections are:

1) Skin and soft tissue: Folliculitis, furuncle (boil), carbuncle, styes , abscess, wound infections, impetigo, paronychia and less often cellulitis.