Gram-Positive Cocci

Question 1

Staphylococci morphology

Answer 1

“Grape-like” clusters

Question 2

Staphylococcus epidermidis: Where are they adept at growing on, coagulase?

Answer 2

Grow as biofilms on prosthetic devices, coagulase-negative

Question 3

Staphylococcus saprophyticus: Key characteristic, coagulase

Answer 3

UTIs in young women, coagulase-negative

Question 4

S. auereus metabolism

Answer 4

Facultative anaerobe

Question 5

Staphylococcus aureus DP

Answer 5

TSST-1, staphylococcal enterotoxins, exfoliatin, alpha-toxin, coagulase (TEEAC)

Question 6

TSST-1 - What does it cause and how does it work?

Answer 6

Causes staphylococcal toxic shock syndrome, Exotoxin, Superantigen -> Release cytokines -> Fever, shock, organ failure

Question 7

Staphylococcal enterotoxins - What do they cause and how do they work?

Answer 7

Cause staphylococcal food poising, Act on neural receptors in upper GI tract -> stimulate vomiting center, Superantigens

Can also cause TSS

Question 8

Exfoliatin: What does it cause?

Answer 8

Scalded skin syndrome

Disrupts intercellular junctions in the skin (splitting of the epidermis between the stratum spinosum and stratum granulosum)

Question 9

Alpha-toxin (alpha-hemolysin): What is it?

Answer 9

Hemolysin - causes lysis of RBCs

Subset of hemolysin - pore-forming toxin

Question 10

Coagulase: What does it result in?

Answer 10

Contributes to the fibrin capsule surrounding abscesses, prevents neutrophils from accessing bacteria

Question 11

Staphylococcus aureus clinical disease

Answer 11

Skin and soft tissue infections (cellulitis, furuncle/carbuncle), endocarditis (common in IV drug users), joint and bone infections (septic arthritis, osteomyelitis), TSS, Staphylococcal food poisoning, scalded skin syndrome, hospital-acquired pneumonia (leading cause)

Question 12

Staphylococcal Toxic Shock Syndrome Signs and Symptoms

Answer 12

Rash, desquamation (peeling) of the skin upon resolution, associated with tampon use (TSST-1), wound infections (enterotoxins or TSST-1), blood cultures often negative

Question 13

Endocarditis characteristic signs

Answer 13

Splinter hemorrhage, conjunctival petechiae, Osler’s nodes, Janeway’s lesions

Question 14

Staphylococcus aureus diagnostic laboratory tests (Morphology, color, catalase, coagulase)

Answer 14

Gram-positive cocci in clusters, gold color colonies, catalase-positive, coagulase-positive

Question 15

Staphylococcus aureus treatment

Answer 15

Drainage of collections of pus

Antibiotics (Penicillin derivatives resistant to S. aureus beta-lactamases - Antistaphylococcal penicillins, cephalosporins)

Question 16

MRSA (mechanism, treatment)

Answer 16

Methicillin-resistant, make variant penicillin-binding protein (PBP2)

Treat with vancomycin, linezolid, daptomycin

Question 17

Patterns of hemolysis used by streptococci

Answer 17

Alpha (Partial clearing), Beta (Complete clearing), Gamma (No clearing)

Question 18

Alpha hemolytic streptococci

Answer 18

Streptococcus pneumoniae, viridans streptococci

Question 19

Streptococcus pneumoniae characteristics (morphology, what does it make)

Answer 19

Gram-positive diplococci

Make pneumolysin - degrades hemoglobin to a greenish pigment

A leading cause of community-acquired pneumonia

Question 20

Viridans Streptococci characteristics: What do they cause?

Answer 20

Some are normal flora of the mouth

(Leading cause of) bacterial endocarditis

Abscess formation

Question 21

Gamma hemolytic streptococci: What do they cause?

Answer 21

S. gallolyticus, blood infections associated with GI cancers

Question 22

Beta hemolytic streptococci (2 groups)

Answer 22

Groups based on surface carbohydrates (Lancefield grouping)
Group A: S. pyogenes
Group B: S. agalactiae

Question 23

Streptococcus pyogenes characteristics (where does it grow, morphology)

Answer 23

Extracellular pathogen, Gram-positive cocci in chains

Question 24

S. pyogenes determinants of pathogenicity

Answer 24

Streptolysin, M-protein, SPEs, Streptokinase

SMSS

Question 25

Streptolysin types

Answer 25

SLO - forms pores in plasma membranes of human cells, SLS

S. pyogenes

Question 26

M-protein description: What do they do?

Answer 26

Fibrillar molecules extend out beyond surface of the bacterium, prevent phagocytosis

Question 27

SPEs (what do they cause)

Answer 27

Streptococcal pyrogenic exotoxins (SPE A, SPE B, SPE C), rash of scarlet fever, streptococcal toxin shock syndrome

Also called erythrogenic toxins, scarlet fever toxins

Question 28

SPE A and SPE C description (What are they?)

Answer 28

Superantigens (may contribute to hypotension and shock), carried by phage

Question 29

SPE B description (What is it and what does it cause?)

Answer 29

Protease, may contribute to necrotizing fasciitis

Question 30

Streptokinase mechanism

Answer 30

Lysis of fibrin clots -> dissemination

Question 31

Streptococcus pyogenes clinical disease

Answer 31

Streptococcal pharyngitis, scarlet fever, streptococcal toxic shock syndrome, skin and soft tissue infections

Question 32

Streptococcal pharyngitis non-suppurative sequelae

Answer 32

Rheumatic fever, post-streptococcal glomerulonephritis (Use antibiotics to prevent non-suppurative sequelae)

Question 33

Scarlet fever characteristics

Answer 33

Erythematous, “sand-paper” rash, circumoral pallor, rash accentuated in skin creases, “strawberry tongue”

Question 34

Streptococcal versus Staphylococcal toxic shock syndrome

Answer 34

Rash rarely present, not associated with tampon use, majority of patients are bacteremic and have associated soft-tissue infection

Question 35

S. pyogenes skin and soft tissue infections (Different layers)

Answer 35

Impetigo, erysipelas, cellulitis, necrotizing fasciitis, myositis

Question 36

Impetigo characteristics

Answer 36

Infection of epidermis, weeping lesions

Question 37

Erysipelas characteristics

Answer 37

Indurated, erythematous rash, well demarcated, rapidly enlarging, usually on face

Question 38

Cellulitis characteristics

Answer 38

Involves dermis and subcutaneous tissues, associated with fever and lymphangitis

Question 39

S. pyogenes non-suppurative sequelae

Answer 39

Acute rheumatic fever (attacks begin about 3 weeks after onset of pharyngitis - does not follow soft-tissue infections, diagnosed by Jones criteria) - erythema marginatum

Poststreptococcal glomerulonephritis - follows infection with either respiratory or skin strains

Question 40

S. pyogenes diagnostic laboratory tests (Morphology, catalase)

Answer 40

Gram-positive cocci in chains, culturable on blood agar plates (beta-hemolysis, catalase-negative), anti-SLO antibody titers

Question 41

S. pyogenes treatment

Answer 41

Penicillin (Plus clindamycin for severe infections, may inhibit production of SPEs)

Question 42

Streptococcus agalactiae - what does it cause?

Answer 42

Cause neonatal sepsis and neonatal meningitis, normally colonize the vagina

Question 43

Enterococci species

Answer 43

E. faecalis and E. faecium

Question 44

Enterococci determinants of pathogenicity

Answer 44

Vancomycin-resistant enterococci, VanA operon (Vancomycin cannot bind to D-Ala-D-lactate)

Question 45

Enterococci clinical disease

Answer 45

Bacteremia, endocarditis, UTIs, intra-abdominal infections, wound infections

Question 46

Enterococci diagnostic laboratory tests

Answer 46

Easily grown on blood agar, grow in presence of high concentrations of bile salts and sodium chloride

Question 47

Enterococci treatment

Answer 47

Antibiotic resistance especially problematic, penicillin/ampicillin + aminoglycosides for bactericidal activity, linezolid, daptomycin