Transcript Staphylococcus aureus - Mississippi University for Women

Staphylococcus aureus
Food Poisoning
St. aureus and food poisoning
• St. aureus causes gastro-enteritis
• Food poisoning is not caused by the
organism but by the toxin that the
organism secretes
• St. aureus food poisoning is the most
common form of food poisoning in the US
Properties of Staphylococcus
aureus
• Gram positive cocci arranged in grape like
clusters
• Non-sporulating
• Colonies on TSA are small, creamy and
golden colored
• Colonies on MSA are yellow and turns the
media yellow
Properties of St. aureus that make
it persistent in nature
• Relatively heat resistant
• Resistant to high concentrations of salt
• Can survive long periods on dry inanimate
objects
2 Case Studies
• What were the symptoms of food
poisoning?
• How did the chefs contaminate the food?
• How did the chef get a staph infection?
How did the chef get a staph
infection?
• Staph is found on any inanimate surface
• Staph is often found associated with the external nares
of 30% of the human population
• Staph is often found on skin surfaces because they can
tolerate the low moisture and high salt content of skin
• Staph can easily spread from person to person via hand
to hand contact
• Staph can penetrate the deep tissues of skin damaged
by
burns
cuts
insect bites
skin diseases—acne, psoriasis, eczema
What happens when Staph enters
a wound and how does this relate
to food poisoning ?
• Localized staph infection leading to an abscess
(collection of pus)
boils=abscesses in the skin
carbuncle=interconnected abscesses
• Rupture of the abscess leads to the release of
live bacteria and associated toxin
How do abscesses and boils form?
• Chef cuts arm and Staph enters deeper skin
layer
• St. aureus is surrounded by a capsule
thick slime layer that prevents an immediate
immune response
• Bacteria multiply at the site surrounded by the
capsule
• St. aureus establishes intimate contact with skin
cells via bacterial techoic acids and fibronectin
skin cell receptors
Abscess and boil formation (cont’d)
• St. aureus produces coagulase which
converts soluble fibrinogen in plasma to
insoluble matrix fibrin
• There are two types of coagulase
bound coagulase on the surface of
the bacteria causes the bacteria to
clump together
free coagulasesecreted from the
bacteria into the environment
Why produce coagulase
• Bound coagulase causes bacteria to clump
together. Why?
the more bacteria in a given location the more effective they
are in 1. shielding each other from an immune response and in
2. excreting toxic factors in high quantities
• Free coagulase causes a protective fibrin clot to
form around bacteria. Why?
bacteria can grow and divide in protective environment; most
immune cells have been denied entry to the region
Pus formation is due to an immune
response inside the fibrin clot
• Many bacteria are found in
fibrin clot
• Also some immune cells did
get trapped in fibrin clot
• Immune cells want to kill St.
aureus
• St. aureus wants to kill immune
cells
• The war that ensues leads to
pus formation
• Pus consists of dead and living
St. aureus, dead neutophils
and plasma inside a fibrin clot
Pus formation continued
The WAR
• The immune cells killing St. aureus
neutrophils surround bacteria, ingest them and produce lysosomal
enzymes that kill bacteria.
This releases bacterial components that lead to a greater
inflammatory response which kills host cells.
• St. aureus killing immune cells
when neutrophils ingest bacteria the lysosome fuses with the
phagosome
St. aureus produces catalase that converts hydrogen peroxide into
water and oxygen
St. aureus produces cytotoxins that kill the neutorphils
The dead neutrophils release lysosomal campartment enzymes that
will may kill St. aureus but will kill adjacent host cells
St. aureus and food
• Staph grows and divides in food and
produces an enterotoxin
• The Staph doesn’t cause food poisoning,
the enterotoxin does
• Enterotoxin is stable to heating at 100oC
for 30 minutes.
• Enterotoxin is resistant to degradation by
stomach gastric acids
Staph enterotoxin causes gastroenteritis in two ways
• VOMITINGtoxin works on the vomiting control
center of the brain this leads to reversal of
peristalsis and vomiting
• DIARRHEAenterotoxin is a superantigen and
elicits a strong immune response in the region
where the toxin is most concentrated. Immune
response causes a loss of brush borders in
intestinal epithelial cells; these cells cannot
absorb water from the gut.