Staphylococci-Pumerantz

Question 1

What are the basic characteristics of staphylococci?

Answer 1

1. Genus: Staphylococcus; Family: Micrococcaceae
2. Greek staphylé (“bunch of grapes”)-Random plane of cell division with cells remaining attached leading to grape-like clusters.
3. Belong to Bacillus-Lactobacillus-Streptococcus cluster: Gram-positive bacteria with a low guanidine-cytosine (G+C) content
4. Peptidoglycan-bound teichoic acids
5. Non-sporulating, non-motile
6. Sensitive to lysostaphin-A glycylglycine endopeptidase produced by Staphylococcus staphylolyticus that cleaves pentaglycine cross bridges found in staphylococcal peptidoglycan
7. Un-encapsulated or limited capsule

Question 2

What differentiates Staphylococci from Streptococci?

Answer 2

Catalase production:
•Present in staphylococci.
•Anti-phagocytic by converting H2O2 ⇒ H2O + O2
•Survive w/n eukaryotic phagocytic cells (neutrophils/macrophages).

Question 3

What does coagulase production determine? Which staph is coagulase +? What are the 2 forms of coagulase? What is the function of each form?

Answer 3

Determines which type of Staph.
Coagulase-positive = S. aureus.
1. Free form (tube test) secreted extracellularly
•Acts with a rabbit plasma protein to cleave fibrinogen and coagulate plasma.
2. Bound form (clumping factor slide test) exists on cell wall
•Converts fibrinogen to fibrin; clumps bacteria
•Cloaks surface bound opsonins from phagocytosis
•Important in endocarditis pathogenesis

Question 4

What are the 3 coagulase-negative staphylococci? Which one is susceptible to Novobiocin? Which one is resistant to Novobiocin?

Answer 4

1. S. epidermidis: Novobiocin-susceptible
2. S. saprophyticus: Novobiocin-resistant
   •#2 cause of UTI in sexually active young women
   oNormal flora of genitourinary skin
   oAffinity for uroepithelial cells
3. S. lugdunensis:
   •Virulence similar to S.aureus

Question 5

What are the 2 medically important staphylococci?

Answer 5

1. S. epidermidis

2. S. aureus

Question 6

What are the 6 identifying characteristics for S. epidermidis?

Answer 6

1. Coagulase-negative
2. Skin colonizer (common blood culture contaminant)
3. Non-hemolytic, white colonies (i.e., no carotenoids)
4. Non-mannitol fermenting
5. Possess a capsule
6. Produce glycocalyx biofilm (“slime layer”)
   •Adherence to foreign bodies (e.g., prosthetic devices)
   •Quorum-sensing: communicating w/ organisms.
   •Barrier to phagocytosis and β-lactam/glycopeptide agents

Question 7

What are the 8 identifying characteristics for S. aureus?

Answer 7

1. Coagulase positive.
2. Carotenoids cause pale golden yellow (Latin: “aurum”) pigmented colonies when grown aerobically at room temperature
3. Grow rapidly under aerobic and facultatively anaerobic conditions
4. β-hemolytic on sheep blood agar (complete hemolysis)
5. Very adaptive to humans (resistant to drying, grow in 8.5% NaCl).
6. Ferments mannitol
7. Reservoirs:nasopharynx, perineum/groin
8. Colonize skin and mucous membranes
   •20% healthy people are persistent carriers
   •30% are intermittent in any given individual
   •50% are non-carriers

Question 8

What are the cell wall components of S. aureus?

Answer 8

1. Biofilm
2. Polysaccharide capsule:
   oTypes 5 and 8 (~75% isolates)
   oAnti-phagocytic
3. Teichoic acids (TA):
   oPolymers of ribitol phosphate
   oMediates attachment to mucosal surface binding to fibronectin
   oRole in inducing shock
4. Lipoteichoic acids (LTA):
   oTriggers release of cytokines from macrophages and other cells
   oDecorated with D-alanyl, repulse cationic antimicrobial peptides (CAPs)

Question 9

What 6 features do S. aureus use to evade the immune system?

Answer 9

1. Carotenoid pigment: resists oxidative burst killing (ROS) which help to survive in macrophages and phagocytes.
2. Protein A: takes Fc portion of antibody and camouflages itself with the body’s own stuff.
3. Clumping factor: makes it coagulase positive.
4. Fibronectin-binding protein A: bind to mucous membranes.
5. Capsule: prevent phagocytosis.
6. Hemolysis: to get into cells.

Question 10

What cytotoxin does S. aureus use?

Answer 10

α-hemolysin: creates a pore into host cells.

Question 11

What enzymes does S. aureus use? What are they used for?

Answer 11

Used to take substrates from the host.

1. Hyaluronidase: spreading factor, allows hyaluronic acid (component of connective tissue) to be degraded so that the organism can go thru.
2. Coagulase: clotting or clot digestion. Engulfs itself in clot.
3. Nuclease: break down DNA for energy.
4. Staphopains: stimulate bradykinin (bring in blood supply).

Question 12

What do superantigens do?

Answer 12

increase cytokine production

Question 13

What are enterotoxins?

Answer 13

• “Pre-formed”
• Resist boiling, cooking, and gastric acid
• Target neural receptors in upper GI tract to stimulate vomiting center in brain

Question 14

What is toxic shock syndrome toxin-1?

Answer 14

• Shares properties with enterotoxins
• Life-threatening.
• Usually localized with BP drop, and other out-of-proportion symptoms.
• Menstrual/non-menstrual`

Question 15

What are exfoliatins?

Answer 15

• SSSS & bullous impetigo
• Protease cleaves desmoglein in epidermal desmosomes in strata granulosum of keratinized epidermis.
• Get shedding of skin in neonates.
• Localized = blisters.