Transcript Staphylococcus aureus

Coccus
Zooming in pyogenic coccus:
disease and pathogenesis
Pyogenic coccus
Pyogenic coccus
Major pathogenic species
Staphylococcus (the staphylococcus)
Staphylococcus aureus
Staphylococcus epidermidis
Staphylococcus saprophyticus
Streptococcus (the streptococcus)
Streptococcus pyogenes
Streptococcus pneumoniae (the pneumococcus)
Neisseria (the neisseria)
Neisseria meningitidis (the meningococcus)
Neisseria gonorrhoeae (the gonococcus)
Staphylococcus aureus
Diseases
Pathogenesis
Roles of bacterial virulent factors
Diagnosis
Methods for bacteria classification
Treatment and prevention
Issues
Bacteria morphology
Staphylococcus :
grape-like irregular
clusters
Streptococcus :
chains or pairs
Neisseria : kidneyshaped diplococci
Bacteria culture: pigmentation
The bacteria produces liposoluble pigments
which make the colonies appear in certain
color:
Staphylococcus aureus
golden yellow
Staphylococcus epidermidis
white
Staphylococcus saprophyticus
white or lemon yellow
Bacteria culture: mannitol fermentation
Biochemical reactions:
for example,
Staphylococcus aureus
is capable of using
sugar mannitol (甘露醇)
as a food source and
will produce acidic
byproducts of
fermentation that will
lower the pH of the
media.
Staphylococcus aureus, Staphylococcus epidermidis,
Streptococcus pneumoniae and Streptococcus
pyogenes on mannitol salt agar plates (containing
7.5% NaCl, mannitol and phenol red).
Diseases
I. Suppurative infections
(化脓性感染)
II. Toxicoses
(毒素性疾病)
I. Suppurative infections
Local infections (contained at the local)
Superficial skin lesions such as sore (疮),
furuncle (疖) and stye (睑腺炎，麦粒肿)
Systemic infections (spread through the blood
stream)
Septicemia (败血症)
Pyemia (脓血症): spread to different organs to
cause pneumonia (肺炎), mastitis (乳腺炎),
phlebitis (静脉炎), meningitis (脑膜炎), urethritis
(尿道炎) and abscesses (脓肿)
II. Toxicoses
Food poisoning
A gastrointestinal illness. Symptoms include nausea,
vomiting, stomach cramps, and diarrhea.
Toxic shock syndrome (TSS,毒性休克综合征)
Characterized by a sudden onset of fever, chills, vomiting,
diarrhea, muscle aches and rash. It can rapidly progress to
severe and intractable hypotension and multisystem
dysfunction. Commonly occurs in women.
Scalded skin syndrome (SSS, 烫伤样皮肤综合症)
Caused by staphylococcal skin infection. The skin blisters
and peels off as though burned. Additional symptoms are
fever, chills, and weakness. commonly occurs in infants.
Pathogenesis
Cell wall virulent factors
Staphylococcal protein A (SPA)
Coagulase
Exotoxins
Staphylolysin (cytolytic)
Leukocidin (cytolytic)
enterotoxin (superantigen)
toxic shock syndrome toxin 1 (superantigen)
Exfoliatin (superantigen)
Staphylococcal protein A (SPA)
Surface bound (in the cell wall) or free
proteins.
Bind to Fc portion of IgG from human,
mouse and guinea pig (but not to that
from rabbit), and thus inhibit Fc
receptor-mediated phagocytosis by
macrophages.
Inhibition of phagocytosis
Fc receptor
SPA
IgG
Agglutination test
In this test, antiStaphylococcus
aureus IgG can
bind SPA using Fc
fragment and the
bacteria through
Fab to from
complexes that can
been seen with
eyes.
Coagulase
Bound (in the cell wall): catalyzes fibrinogen
(纤维蛋白原) into fibrin (纤维蛋白). Cause
coating of the bacteria with fibrin and thus
inhibit phagocytosis and killing mediated by
serum components.
Free: secreted and turns into
staphylothrombin after activation by cofactors
in the plasma, which catalyzes fibrinogen into
fibrin. Cause coagulation of the plasma and
helps to restrain infections at the local.
Coagulase test and CNS
A test of coagulation of human or
rabbit plasma in the presence of
anticoagulant (citrate or heparin).
Coagulase-negative staphylococci
(CNS) used to be thought as nonpathogenic, however, they have
become a major source of hospitalacquired infections:
Staphylococcus epidermidis
Staphylococcus saprophyticus
Cytolytic exotoxins:
staphylolysin and leukocidin
Attack mammalian cell membranes, cause abscess
and tissue necrosis. Often referred to as hemolysins.
Staphylolysins:
Four types: , ,  and 
Staphylolysin ,  and  can lyse erythrocytes (the
basis for hemolytic reaction); toxic to many other
cells such as white blood cells and muscle cells
Staphylolysin : close to leukocidin.
Leukocidin: lyse macrophages and neutrophils.
Hemolysis test
Bacteria are grown on sheep blood agar plates (containing 5% sheep blood):
α- hemolytic reaction,
partial hemolysis with a
green coloration：
Streptococcus pneumoniae
β- hemolytic reaction,
complete hemolysis：
Staphylococcus aureus
Streptococcus pyogenes
γ - hemolytic reaction,
no hemolysis:
Staphylococcus epidermidis most
strains Staphylococcus saprophyticus
Superantigens
Superantigens can bind
both to class II MHC
molecules (but not in
the peptide cleft) and
also to a relatively
conserved region of the
TCR βchain.
This leads to nonspecific activation of 220% of all T cells (vs.
0.01%), and massive
unregulated cytokine
release.
Superantigen exotoxins:
enterotoxin, TSST-1 , and exfoliatin
Enterotoxin, 9 serotypes, responsible
for staphylococcal food poisoning.
TSST-1, close to enterotoxin, cause
toxic shock syndrome (TSS).
Exfoliatin, 2 serotypes, cause
staphylococcal scalded skin syndrome
(SSS).
Diagnosis
Pus
abscesses and superficial skin lesions
Sputum
lower respiratory tract infections
Blood
septicemia, pyemia
Food/feces or vomit
food poisoning
Mid-stream urine
urethritis
S. aureus
CNS
Streptococcus Neisseria
Gram staining
+
+
+
-
bacteria
morphology
irregular
clusters
irregular
clusters
Chains or
pairs
Kidneyshaped
diplococci
colony
pigmentation
Golden
white
mannitol
fermentation
+
-
hemolysis test
β-hemolytic
γ -hemolytic
coagulase test
positive
negative
agglutination
test
Use serum samples from patients.
Treatment and prevention
Antibiotics
MRSA refers to methicillin (甲氧苯青霉素)resistant Staphylococcus aureus, and most MRSA
strains are also multiply drug resistant
Chromosomal mutation
Plasmid-conferred
CNS, eg. Staphylococcus epidermidis
Biofilm formation
Exotoxin neutralizing antibodies
No vaccines available currently