staphylococci

Question 1

three staphylococcus species

Answer 1

1) aureus
2) epidermidis
3) saprophyticus

Question 2

staphylococcus shape and gram stain

Answer 2

all gram positive cocci

Question 3

what is coagulase?

Answer 3

clots human/rabbit plasma by activating fibrinogen

Question 4

which staph species are coagulase positive?

Answer 4

only aureus, the other two are negative

Question 5

what is catalase?

Answer 5

converts peroxide to oxygen and water

Question 6

is staph catalase positive or negative?

Answer 6

positive, in contrast to strep which is negative

Question 7

what is the metabolic characterization of staph?

Answer 7

facultative anaerobe

Question 8

S. aureus, where found?

Answer 8

• skin, mucous membranes, nares of normal individuals

- nasal passages up to 30-40%

Question 9

S. aureus risk factors

Answer 9

• foreign bodies, catheters
• hospitalized/immunocompromised
• diabetes
• drug addiction

Question 10

S aureus pathogenesis of toxin-mediated disease

Answer 10

• enterotoxins via food/tampon

- colonization/toxin production in host - colonization via fibrinogen/fibrinogen receptors on bacteria

Question 11

important S. aureus toxins

Answer 11

• toxic shock syndrome toxin - toxic shock syndrome

- exfoliatins - scalded skin syndrome

Question 12

S. aureus pathogenesis of invasive disease

Answer 12

• bacterial surface adhesion molecules bind to matrix proteins such as fibrinogen, fibronectin, collagen, and platelets
• matrix proteins found on damaged skin, disrupted airway epithelium, or endothelial cells in bloodstream
• after adhesion, colonization, evasion of host response, toxin synthesis, cell lysis, spreading to other sites

Question 13

S. aureus toxins and enzymes for cell lysis

Answer 13

• alpha toxin - lyse membranes
• leukocidins - lysis of leukocytes
• proteases - breakdown of host proteins
• coagulase - clots human plasma
• staphylokinase - lysis of blood clot
• hyaluronidase - dissolve hyaluronic acid, component of matrix
• lipase - dissolve lipids and lipoproteins

Question 14

S. aureus toxins and enzymes for evasion of host immune response

Answer 14

• protein A - cell wall protein binds to host IgG via Fc receptors, less complement-mediated killing, B-cell super antigen leading to defective production of IgM
• enterotoxins A-E, G-I, T-cell superantigens, blunting of T-cell response
• capsular polysaccharides - anti-phagocytic
• Eap (Map) - surface protein that impairs neutrophil recruitment

Question 15

S. aureus toxin-mediated diseases

Answer 15

• food poisoning
• toxic shock syndrome
• staph scalded skin syndrome

Question 16

S. aureus food poisoning causes and clinical syndromes

Answer 16

• enterotoxins A-E, G-I
• can resist boiling
• A and C are super antigens stimulating IL-1, IL-2, TNF
• nausea, vomiting, non-bloody diarrhea

Question 17

S. aureus toxic shock syndrome causes and clinical syndromes

Answer 17

• enterotoxin F (TSST-1)
• tampon use or open wounds
• superantigen stimulates IL-1, 2, TNF
• fever, rash, desquamation of palms and soles, hypertension, shock

Question 18

S. aureus scalded skin syndrome causes and clinical syndromes

Answer 18

• exfoliatins A and B
• only secreted by phage group II
• seen in infants
• erythematous skin, exfoliation
• epidermis detaching from dermis in response to toxin

Question 19

immunological nature of S. aureus toxin mediated infections:

Answer 19

• most caused by super antigen effect so antibiotics often not effective by the time the syndrome is present

Question 20

treatment of staph aureus invasive infections

Answer 20

• surgical drainage of abscesses

- synthetic penicillin, vancomycin as last resort

Question 21

S. aureus colony color

Answer 21

yellow

Question 22

S. epidermidis colony color

Answer 22

white

Question 23

S. saprophyticus colony color

Answer 23

white

Question 24

distinguishing S. epidermidis from S. saprophyticus

Answer 24

S. epidermidis is sensitive to novobiotin, which S. saprophyticus is not.

Question 25

S epidermidis, where found?

Answer 25

skin, normal flora

Question 26

who most susceptible to S. epidermidis?

Answer 26

neonates, patients with renal failure, immunocompromised

Question 27

S. epidermidis pathogenesis

Answer 27

- colonizes prosthetic surfaces very efficiently - bacteremia, but slower than S. aureus - BIOFILM -

Question 28

S. epidermidis clinical syndromes

Answer 28

- low grade fever, pain, discomfort about prosthetics | - may be a contaminant in blood culture so treat patient, not culture

Question 29

treatment for S. epidermidis:

Answer 29

- remove prosthetics if feasible - vancomycin - consider rifampin and/or gentamicin if toxic

Question 30

S. saprophyticus clinical syndromes

Answer 30

- second most common cause of UTI after E. coli | - polyuria, dysuria

Question 31

S. saprophyticus, where found?

Answer 31

skin

Question 32

S. saprophyticus treatment

Answer 32

- trimethoprim sulfamethoxazol (bactrim) | - norfloxacin (quinolone)