Staphylococcus aureus

Most pathogenic Staph cause
infection after a breach in the skin.
A.
PrepTalk Clicker Questions
B.
True
False
Did you Prep?
Which factor is most strongly correlated with
the virulence of pathogenic staphylococci?
A.
B.
C.
D.
E.
Superantigen
Coagulase
Fibrinolysin
Enterotoxin
Hemolysin
Case: Lulu’s Lips
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First Case - Lulu
St. Bernard
4-years-old
Bad breath
Painful, hyperemic
sores on lips
Diagnostic information
Gram stain of colony
BAP 24 hr
1
What is the most probable pathogen
causing this lipfold pyoderma?
What is the most probable pathogen
causing this lipfold pyoderma?
A.
B.
C.
D.
Where did this infection most likely
come from?
A.
B.
C.
D.
E.
F.
Normal flora on Lulu’s skin
Another infected dog
Contaminated dog food
Lulu’s owner
Contaminated water bowl
The darn cat!
More Key Elements of the Story
Penicillin resistance common
penicillinase
Diagnosis: culture
Key test coagulase
Staphylococcus hyicus
Staphylococcus epidermidis
Staphylococcus aureus
Staphylococcus intermedius
Key Elements of the Story
Source = endogenous
Predisposing factor: moisture = skin maceration
Invasion & adherence
Inflammation localized…pain
If untreated, can become chronic
Acute inflammatory: neutrophils …..pus
S. intermedius factors:
Protein A – “backward” Ig binding
Capsule – antiphagocytic
Coagulase – “hides” bact. - coats with fibrin
Hyaluronidase – “spreading factor”
Fibrinogen
Coagulase Testing
Tube test 100% sensitive; Slide test is fast.
Fibrin
Tube test – 3 hours @ 37C
Slide test – minutes at RT
All coagulase-positive Staph = pathogenic
Tube test is definitive; slide test is presumptive
2
Resisting Resistance
Allows penicillin
to remain active
and exert its effect
New Emerging Resistance Problem
MRSA (methicillin resistant Staph aureus)
60%
Clavulanic acid
blocks
penicillinase
% R esistan t
50%
Works based on structural similarity
of penicillin and clauvulanic acid.
Next case
40%
30%
20%
10%
0%
1997
1998
1999
2000
Ursula’s Udder
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Swollen quarter
High SCC
Abnormal
Diagnostic Information
What is Your Diagnosis?
3
Which is most commonly associated with
multiple cases of Staph mastitis in a dairy herd?
A.
Mastitis
Staphylococcus aureus
Key Elements of the Story
B.
C.
D.
Poor hygiene at milking
Purchase of infected cattle
Sand bedding in freestalls
Hot weather
Prevention & Control
Identify infected cows by culture & milk them last
Source = endogenous, endogenous, infected cow
Predisposing factor: milking system
Ascending infection
Inflammation: acute or chronic
Low-grade infections – intermittent shedding
Modest increase in SCC
S. aureus factors:
Protein A – “backward” Ig binding
Capsule – antiphagocytic
Coagulase – “hides” bact. - coats with fibrin
Hyaluronidase – “spreading factor”
Prevention & Control
Antibiotic Therapy in Food Animal
Dry cow treatment
You MUST Consider Withdrawal Times
Ceftiofur
3rd generation cephalosporin
Bacteriocidal vs Gram-pos & Gram-neg bacteria
Witholding time = zero
4
Next case
Case: Got Milk? No – Got Sick!
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14,000 people sick
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Diarrhea
Vomiting
Associated with drinking
low-fat milk
Some complained of
strange smell in milk
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98 hospitalized
True Story
Diagnostic information
High numbers recovered from milk products
What is Your Diagnosis?
Gram stain of colony
BAP 24 hr
What Staph characteristics contribute
to Staph food poisoning?
Food Poisoning
A.
B.
(more correctly food-borne intoxication)
C.
Staphylococcus aureus
D.
Staph grow well in high protein foods
Staph are not inhibited by salt in foods
Staph secrete a potent enterotoxin
All of the above
5
Key Elements of the Story
Source = post-pasteurization contamination
Violation of sanitary practices
Adequate time at ambient temp for S. aureus to grow
Enterotoxigenic strain
Ingestion of adequate dose of toxin
NOT an infection – Food-borne INTOXICATION
Short incubation period (<12 hr)
No need for bacterial growth in patient
Factors Involved in Outbreak
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Workers at dairy plant were found
recycling products returned by large-lot
customers and unshipped products to
make new batches.
Cartons were opened manually with bare
hands and poured into a storage vat for
recycling.
before onset of symptoms
Food Safety Net, June 30 - July 15, 2000.
Staph. aureus Enterotoxin
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30% of Staph aureus strains can produce it.
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Staph grows well in high protein foods.
Not inhibited by salt.
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Heat-stable protein toxin.
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Resistant to proteolytic enzymes.
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Induces nausea, vomiting, diarrhea.
Humans more susceptible to toxin than animals.
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Other Staphylococcus Infections
Similar pathogenesis details
and/or less well defined
pathogenesis.
Survives moderate cooking temperatures.
Survives passage through stomach.
Exudative Epidermitis
Sequence of Events
1. Trauma inoculates Strep hyicus (normal flora)
2. Bacteria adhere via fibronectin-binding proteins
3. Avoids phagocytosis
 Protein A
 Capsule
4. Secretion of exfoliative toxin
5. Host reaction + toxin effects cause massive
exudation leading to dehydration and death.
6
Human Form of Disease
Bumble Foot
Skin scald
Exfoliative toxins: ETA & ETB
Poor housing hygiene
and/or injury
Impetigo
Summary
Major Virulence Factors
 Protein A – “backward” Ig binding
 Capsule – 11 types; polysaccharides; antiphagocytic
 Coagulase – “hides” bact. - coats with fibrin
 Hyaluronidase – “spreading factor”
 Enterotoxins – emesis (vomiting) in humans
 Toxic Shock Toxins = Superantigens – hypotension
 Exfoliative toxin – skin damage
 α Hemolysin / cytotoxin – cell death or damage
Name Changes in 2009
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Old Staphylococcus aureus
New:
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Staph aureus subsp. aureus (most common)
Staph aureus subsp. anaerobius (rare; sheep abscess)
Old Staph intermedius (coag-pos Staph from cats & dogs)
New:
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Staph pseudintermedius (most common)
Staph delphini
Staph intermedius
Name Changes in 2009
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Old Staphylococcus aureus
New:
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Staph aureus subsp. aureus (most common)
Staph aureus subsp. anaerobius (rare; sheep abscess)
Old Staph intermedius (coag-pos Staph from cats & dogs)
New:
Differentiation is very complex and not all that
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Staph pseudintermedius
(most common)
clinically relevant.
Some labs or clinicians
Staph delphinisimply refer to Staph intermedius Group.
Methicillin-resistance can appear in any of these
Staph intermedius
species.
The End
7