Staphylococci

Question 1

staphylococci - overview

Answer 1

*gram positive
*grape-like clusters
*beta hemolytic
*catalase POSITIVE
*differentiate based on coagulase

Question 2

coagulase

Answer 2

cleaves fibrinogen to fibrin in-vitro and in-vivo, forming a clot in serum

Question 3

staph aureus - coagulase test

Answer 3

*coagulase POSITIVE

Question 4

S. aureus - overview

Answer 4

*more virulent strain of staph
*tends to be found where the sun doesn’t shine (nose, armpits, groin)
*infections can be minor or life-threatening

Question 5

S. epidermitis - coagulase test

Answer 5

*coagulase NEGATIVE

Question 6

S. epidermitis - overview

Answer 6

*found on skin of all individuals
*less virulent than s. aureus
*impressive biofilm / SLIME LAYER
*infections tend to be of foreign materials (catheters, prosthetic joints/valves, etc)

Question 7

staph aureus - virulence factors

Answer 7

*techoic acid (proinflammatory)
*protein A (inhibits antibodies and interferes with leukocytes)
*MSCRAMMs (adhesion proteins)
*exfoliative toxins (remove top layer of skin)
*enterotoxins
*TSST-1 (toxic shock superantigen of staph)
*many others

Question 8

staph aureus - pathophysiology

Answer 8

*acquired by direct contact from colonized/infected individual or from a fomite
*colonizes
*invades tissues through toxin and enzyme virulence factors
*under the regulation of an agr operon

Question 9

what operon regulates the expression of staph aureus virulence factors

Answer 9

agr (accessory gene regulator) controls how virulence factors are turned on and off

Question 10

what is the main host defense against staph aureus

Answer 10

**an intact mucosa and integument
*opsonization
*phagocytosis
*neutrophil-mediated killing

Question 11

risk factors for invasive disease of staph aureus

Answer 11

*immunocompromise
*diabetes
*disruption of integument
*IV drug use
*implantable foreign bodies

Question 12

staph aureus - categories of clinical infection

Answer 12

1. toxin-mediated
2. superficial
3. invasive

Question 13

staph aureus - toxin-mediated food poisoning

Answer 13

*not actually due to invasion, but due to toxins (preformed enterotoxin contamination of food)
*includes meats, mayo, custards, etc
*stimulate peristalsis and fluid secretion from GI tract

Question 14

staphylococcal scalded skin syndrome - overview and toxins

Answer 14

*from s. aureus colonization (not invasion/infection)
*caused by exfoliative toxins ETA and ETB
*superficial skin exfoliation presenting as erythema follow by blisters and exfoliation
*nikolsky sign

Question 15

exfoliative toxins ETA and ETB - staph aureus

Answer 15

serine proteases that split the intercellular bridges in the stratum granulosum of the epidermis
*cause staphylococcal scalded skin syndrome

Question 16

staph aureus - toxic shock

Answer 16

*TSST-1 is a superantigen that interacts with the MHC complex
* associated with S. aureus colonization (not infection)
*tampons, wound packing, wound infection
*extreme and life-threatening inflammatory response (fever, nausea/vomiting, rash, organ failure)

Question 17

staph aureus - superficial infections

Answer 17

*often caused by MRSA
-impetigo
-furunculosis
-carbuncles
-skin abscesses

Question 18

staph aureus - invasive infection

Answer 18

*MSCRAMMs facilitate dissemination (through bloodstream)
*bacteremia and endocarditis can be particularly severe
*almost any organ / system can be infected
*MOST COMMON CAUSE OF muscle, bone, joint, and heart valve infections
*post-influenza pneumonia

Question 19

staph aureus - diagnosis

Answer 19

*gram stain of pus or tissue & culture
*PCR blood culture

Question 20

coagulase negative staph

Answer 20

-staph epidermitis
-staph saprophyticus

Question 21

staph saprophyticus

Answer 21

-urinary pathogen (UTIs, esp cystitis) in sexually active females
-part of normal vaginal flora