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micro staph


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-what does aureus mean?
-2 sub groups

-coag positive

-coag neg
-most common?
-referred to as
-produce? 8 things
-what does coag do?
Gram positive cocci in clusters
-differentiated from other B hemolytic bc of gold pigment
B. Catalase positive
C. Divided into two groups: coagulase positive and negative
Coagulase positive = Staphylococcus aureus, (more virulent) Coagulase negative = multiple species, Staphylococcus epidermidis is the most common. In general, the whole list of coagulase negative staphylococci are grouped together and simply referred to in clinical practice as "coag negative staph" or "CNS"
D. Staphylococci produce multiple enzymes that increase pathogenic
potential. Some produce toxins. They may also produce external "slime" that increases their ability to attach to cells and foreign bodies Products of special note:
1. Coagulase: it does clot plasma, and may be part of local tissue destruction in infections
2. Alpha, beta, and gamma hemolysins: lyses human red blood cells in the laboratory, but role in infection not well described
3. Leukocidin: kills or damages white blood cells, may perpetuate infection by blocking normal immune response
4. panton-valentine leukocidin (PVL): a newly recognized toxin associated with more serious skin and soft tissue infections
5. Enterotoxins: five (a-e) are protein products of Staph aureus. When staph is introduced into food by food handlers, the organism may produce one of these toxins and cause acute food poisoning with severe nausea, vomiting, abdominal cramps, prostration, and watery diarrhea
6. Protein A: Binds to IgG. Role?
7. Others: Erythrogenic toxin, lysozyme, hyaluronidase, lipase, DNAse, Dermonecrolysin, beta-lactamases (resists pen), and toxic shock toxin with activities as implied by the names.
Clinical Infections 10

for infection with a CNS, what is required
1. Asymptomatic carriage especially on skin and anterior nares
2. Superficial skin infections: folliculitis, abscesses, furuncles, carbuncles
3. Foreign body infections (stitch abscesses, etc.)
4. Soft tissue infections: cellulitis, fasciitis
5. Osteomyelitis
6. Bacteremia
7. Endocarditis
8. Food poisoning
9. Toxic Shock Syndrome
10. Device associated infections (iv and other catheters, prostheses) To have infection with a CNS, a foreign body is usually required
Clinical manifestations of staphylococci are in 3 categories
suppurative, toxin mediated, and device related
The first two categories almost always occur when , the last
-Staph aureus is the culprit
-with either S. aureus or CNS
Suppurative infections
are those in which the organism leads to an inflammatory response, the site is invaded by white blood cells, and "pus" is produced (infections 1-7 above).
Toxin mediated infections are
the result the toxins produced by staph that lead to a tissue response (items 8 and 9).
Predisposing factors to infection
1. Suppurative infections
are more likely to occur when any foreign body (sutures, gauze, bandages, IV catheters, artificial joints, bone stabilizing hardware, artificial graft material, etc.) is present.
Resistance of Staph aureus to semisynthetic penicillins, like
methicillin, nafcillin, and oxacillin is termed
. Laboratory Diagnosis
1. Gram stain helpful
2. Grows readily on laboratory media
3. Catalase and coagulase are primary tests
have to be wary of superficial culture results:
staphylococci are common skin flora
which staf is more likely to cause infection?
Staph aureus are more likely to cause disease than CNS, but either can simply be colonizing the surface rather than causing infection; growth of the same organism from multiple cultures is more likely to be real

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