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Microbiology

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Gram Positive Cocci

Question
7 out of 78
 

Boils are caused by following organism:



A E.coli

B Streptococcus

C Staphylococcus

D Klebsiella

Ans. C Staphylococcus

Most common cause of pyogenic skin infection is S. aureus. It is also the commonest cause of folliculitis, sycosis barbae, stye, carbuncle and furuncle.

EXTRA EDGE

ON VIRULENCE FACTORS OF S. AUREUS:

Cell-wall associated-

Cell-wall associated structures

Activity

Peptidoglycan

Inhibits inflammatory response

Teichoic acid

Adherence to mucosal surfaces

Protein A

Reacts with Fc region of IgG

Clumping factor

Binds to fibrinogen

EXTRACELLULAR FACTORS-

hemolysin

- Inactivated at 70°C, reactivated paradoxically at 100°C

- Lyses rabbit, sheep and human red blood cells

- Leucocidal, cytotoxic, dermonecrotic, lethal

hemolysin

- Sphingomyelinase;Lyses sheep, but not human or rabbit red blood

cells; Exhibits hot-cold phenomenon

hemolysin

- Lyses rabbit, sheep and human red blood cells

hemolysin

- Lyses rabbit, sheep and human red blood cells

Leucocidins

- Two components F & S

- Damage polymorphonuclear leukocytes & macrophages

Epidermolytic toxin (Exfoliative toxin)

- Mainly belong to phage group II

- Two types

- ET-A: 30,000 daltons, heat stable, chromosomal gene

- ET-B: 29,500 daltons, heat labile, plasmid controlled

Enterotoxins

- Produced by 40% of clinical isolates, heat stable(100C x 10-40min

- Cause food poisoning; nine antigenic types (A,B,C,D,E,G,H,I,J)

Toxic shock syndrome toxin 1

- Most strains producing it belong to phage group I

- 22,000 daltons

- Earlier called as enterotoxin F

Extracellular enzymes

Activity

Free Coagulase

- Activate coagulase reacting factor normally present in plasma

- Clots plasma by converting fibrinogen to fibrin

- Eight antigenic types (A-H)

Staphylokinase (fibrinolysin)

- 13,000-15,000 daltons

- breaks fibrin clots & allows spread of infection

Hyaluronidase

- >90% strains produce

- hydrolyses hyaluronic acid; facilitating spread of infection

Deoxyribonuclease

- Degrades DNA

Lipase

- Degrades lipid

Phospholipase

- Degrades phospholipids

Proteases

- Degrades proteins

Gram Positive Cocci Flashcard List

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