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64 Cards in this Set
- Front
- Back
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T/F Most staphylococci are penicillin G resistant
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T
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Staph are gram (pos, neg)
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pos
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How are staph arranged?
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in grape-like clusters as seen on gram stain
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Staph are catalase (positive, negative)
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Positive (visualize a hospital staff (staph) posing for a group photo with a cat)
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How can Staph Aureus be identified from other beta-hemolytic cocci?
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They show a gold pigment when cultured on sheep blood agar
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Three major pathogenic staph species
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S aureus, S epidermidis, S saprophyticus
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Beta-hemolytic: defn
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completely hemolyze red blood cells on agar plate
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How are more virulent staph species (staph aureus) differentiated from less virulent (staph epidermidis, S. saprophyticus)?
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Coagulase test. The more virulent species tends to clump together
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Coagulase converts ___ to ____ causing the plasma to coagulate
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fibrinogen to fibrin
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protein having sites that bind the Fc portion of IgG, protecting organism from opsonization and phagocytosis
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Protein A
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Enzyme that can lead to fibrin formation around the bacteria, protecting it from phagocytosis
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Coagulase
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Proteins destroying RBCs, neutrophils, macrophages, platelets
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hemolysins
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Proteins destroying leukocytes
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leukocidins
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secreted form of beta-lactamase, disrupting penicillin molecule, thereby inactivating penicillin
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Penicillinase
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What does penicillin binding protein (aka transpeptidase) do?
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Necessary for cell wall formation. It's inhibited by Penicillin.
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What proteins does Staph use to tunnel thru tissue?
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hyaluronidase (spreading factor); Staphylokinase (lyses formed fibrin clots); Lipase (degrades fats and oils, facilitating colonization of sebaceous glands); Protease (destroys tissue proteins)
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Diffusible exotoxin that causes skin to slough off
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Exfoliatin (scalded skin syndrome)
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Exotoxins that cause food poisoning, resulting in vomiting an diarrhea
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Enterotoxin
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Exotoxin causing Toxic Shock Snydrome, found in 20% of Staph aureus isolates.
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Toxic Shock Syndrome toxin (TSST-1)
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How long does gastroenteritis last?
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12-24 hours of vomting, nausea, diarrhea, abdominal pain, occasionally fever
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Toxic Shock Syndrome Symptoms
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sudden onset of high fever, nausea, vomiting, watery diarrhea (enterotoxin like syndrome), followed in a few days by diffuse erythematous rash, desquamation. Also associated with septic shock
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Why are antibiotics not curative in toxic shock syndrome?
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because it is the exotoxin, not the bacteria, that causes the clinical manifestations
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Protein that lyses formed fibrin clots
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Staphylokinase
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protein breaking down proteoglycans in CT
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Hyaluronidase
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enzyme degrading fats and oils that accumulate on body surface
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lipase
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What is Staphylococcal Scalded Skin Syndrome?
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Staph aureus strain productive exfoliative toxin A and B, established localized infection and releases a diffusible toxin that exerts distant effects. Usually affects neonates with local infection of the recently severed umbilicus or children. Healing is rapid and mortality is low
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exfoliative toxin A and B causes what disease?
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Staphylococcal Scalded Skin Syndrome
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rare but severe causes of community-acquired pneumonia. usually follows a flu URI.
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s. aureus
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violent destructive infection of heart valves with sudden onset of high fever, chills, myalgias.
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acute endocarditis
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acute endocarditis is more likely to be caused by staph ______ while chronic endocarditis is more likely to be caused by Strep _________ and ________
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Aureus; viridans and Group D Strep.
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What serious illnesses can be caused by s. aureus?
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pnemonia; meningitis/cerebritis/brain abscess; osteomyelitis; acute endocarditis; septic arthritis; skin infections; blood and catheter infections
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Minor skin infections almost always caused by what?
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s aureus or strep pyogenes (Group A beta-hemolytic)
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Contagious infection usually occuring around the mouth characterized by vesicles becoming pustules, which crust over to become honey-colored, wet, and flaky.
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impetigo
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Why are most staph penicillin resistant?
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Because they secrete penicillinase
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What is MRSA? What is it mediated through?
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methicillin-resistant staph A. It's often resistant to nafcillin to. Mediated thru chromosomal DNA segment (mecA) encoding a new penicllin binding protein 2A that can take over the job of peptidoglycan cell wall assembly when the normal penicillin binding protein is inhibited.
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What kind of selective pressure do broad-spectrum antibiotics cause?
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Favors multi-drug resistance in bacteria, usually acquired by plasma exchange.
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One of the few antibiotics useful in treating MRSA
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vancomycin
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chromosomal DNA segment encoding a new penicllin binding protein 2A carried by MRSA
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mecA
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chromosomal transposon DNA segment encoding a series of proteins modifying D-alanine-D-alanine terminus, changing to D-alanine-D-lactate, which has low affinity for vancomycin. Results in VRSA.
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vanA
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part of normal bacterial flora, frequent skin contaminant of blood cultures
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Staph epidermidis
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Staph a:
1) Coagulase (pos, neg) 2) Catalase (pos, neg) 3) Metabolism type |
1) Pos
2) Pos 3) Facultative anaerobe |
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Staph epidermidis:
1) Coagulase (pos, neg) 2) Catalase (pos, neg) 3) Metabolism type |
1) neg
2) pos 3) facultative anaerobe |
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Staph saprophyticus:
1) Coagulase (pos, neg) 2) Catalase (pos, neg) 3) Metabolism type |
1) neg
2) pos 3) facultative anaerobe |
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most frequent organism isolated from indwelling prosthetic devices
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Staph epidermidis
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extracellular polysaccharide network, simliar to capsule polysacchardies, forming mechanical scaffold around bacteria
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biofilm
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Leading cause of UTIs in young women (after e coli)
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Staph saprophyticus
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How to treat Staph saprophyticus
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penicillin
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How to treat Staph epidermidis
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vancomycin (it's resistant to multiple antibiotic)
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Only S. ____ is Clumping Factor positive
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aureus
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Immune deficiencies predisposing people to staph infections
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1) Hypo or agammaglobulinemia
2) Job's disease 3) Chronic granulomatous disease 4) Chediak-Higashi syndrome 5) diabetes |
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characteristic pathologic lesion caused by staph
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abscess
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S aureus attracts and is killed by ________
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PMNs (neutrophils)
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What is polysaccharide intercellular adhesin?
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loosly associated exopolysaccharide, plays role in biofilm formation
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considered major virulence factor of S epidermidis
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biofilm formation
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distinguishes staph from strep
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catalase (staph is pos)
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S. aureus carried on what %age of normal people?
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30-40%
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most common cause of pyogenic skin infections
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s. aureus
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More common cause of spreading infections like cellulitis, necrotizing fasciitism, impetigo
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Group A Strep
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What drugs used for methicillin sensitive S aureus? (MSSA)
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semisynthetic peniciliniase-resistant penicillins, cephalosporins
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Most common cause of nosocomial bacteremia
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Staph
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Major toxins associated with S aureus
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• Superantigens
- Toxic Shock Syndrome Toxin (TSST) - Staphylococcal Enterotoxins (eg. SEB) - Exfoliatin • Pore-forming toxins - Alpha and gamma toxin (hemolysins) - Panton-Valentine leukocidin |
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Daptomycin is used to treat what?
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Highly resistant gram-positive species (eg., MRSA, VRSA)
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CoNS
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coagulase-negative staphylococcus (CoNS) - anything other than staph aureus
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How is S saprophyticus Distinguished from other CoNS?
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Distinguished from other CoNS by novobiocin resistance
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