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staphylococci

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staphylococci disease characteristics lab diagnosis Treatment And everything you need to know

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  • February 21, 2016
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  • 2015/2016
  • Lecture notes
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Bkryshadoul
Staphylococci
1. Staph. Aureus ​ :
● Characteristics​ :
i. Gram +ve \ catalase +ve \ coagulase +ve \ cocci in clusters \
haloduric "tolerate salts" \ ​ beta hemolytic​ ,​
mannitol fermenter​ .
ii. Optimum growth temp. 35 c
iii. Non capsulated "but some are, thus serotyping isn’t that useful".
iv. Have a golden color in blood agar, this is due to production of
carotenoid pigment called ​ staphyloxanthin​ , that inactivate
bactericidal products of the WBCs.
v. Normally found as commensal in the nose or in female genitals
tract.
● Virulence factors​ :
● Structural ​ :
a. Protein A ​ , principle of coagulase test, binds to Fc portion
of IgG, thus activation of complement system is
prevented, and thus opsonization and phagocytosis are
prevented.
b. Teichoic ​ acid, mediate adherence to mucosal membranes,
Lipoteichoic​ acid is important in induction of septic shock
by inducing the release of cytokines like IL‐1 and TNF,
from macrophages .
c. Peptidoglycans​ , has an ​
endotoxin​ like activity, by binding
to macrophages it induce the release of cytokines and
coagulation cascade, explains why ​ Sta. Aureus ​ can cause
septic shock without having endotoxins.
d. Fibronectin binding protein :​ enables the bacteria to bind
to the fibronectin of the endocardium of the heart volves,
(the only cause of acute endocarditis)
● Toxins​ :
a. Superantigens​ :
i. Enterotoxin​ ,​

heat stable, acid resistant, that cause
release of large amounts of IL‐1 and IL‐2 from
macrophages and helper T cells, respectively, this
stimulates enteric neurons to stimulate the vomiting
center in the brain.
ii. TSST‐1​ , causes toxic shock syndrome, only 20 % of
staph. Aureus have the gene for this toxin. TSST is a
superantigen and causes toxic shock by stimulating

, the release of large amounts of IL‐1, IL‐2, and TNF,
antibodies against TSST are found.
b. Exfoliatin​ , cause separation of the skin at stratum
granulosum, causing ​ scalded skin syndrome​ and ​
impetigo​
.
c. Leukocidins toxins​ , are two:
i. Alpha toxin​ , forms a hole in the cells causing
necrosis of skin and hemolysis, by forming pores on
the cell membrane.
ii. P‐V leukocidin​ , it’s gene is located in a lysogenic
phage, this toxin form a hole in cell membrane
causing death of cells especially WBCs, causes of
necrotizing pneumonia.
● Enzymes ​:
a. Beta lactamase​ , the cause of penicillin resistance.
b. Catalase​ , causes the break of H​ 2O​
​ 2.​
c. Hyaluronidase​ , spreading factor, causes breaking of
hyaluronic acid thus make penetration easy to
subcutaneous tissue.
d. Coagulase​ , either
i. bound​ "clumping factor," facilitate binding to
surfaces and cause clumps in plasma.
ii. releasable​ , induce formation of plasma clot that
forms a protective wall around the bacterium
inhibiting leukocytes migration, by activating
prothrombin to thrombin, which activate fibrinogen
to fibrin.
e. Fibrinolysin​ , AKA ​ staphylokinase​ , breaks blood clots.



● Diseases​:
i. Pyogenic diseases ​ :
● Conjunctivitis​ typically presents with unilateral burning eye
pain, hyperemia of the conjunctiva, and a purulent
discharge."most common cause".
● Sepsis​, with clinical features that of gram ‐ve rods.
● Acute Endocarditis​ may occur on normal or prosthetic heart
valves, especially right‐sided endocarditis (tricuspid valve) in
intravenous drug users.
● Osteomyelitis and septic arthritis​ (old individuals and children)
may arise either by hematogenous spread from a distant
infected focus or be introduced locally at a wound site, ​ the most
common cause of septic arthritis in adults is S. Aureus​ .

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