Staphylococci-Pumerantz Flashcards
What are the basic characteristics of staphylococci?
- Genus: Staphylococcus; Family: Micrococcaceae
- Greek staphylé (“bunch of grapes”)-Random plane of cell division with cells remaining attached leading to grape-like clusters.
- Belong to Bacillus-Lactobacillus-Streptococcus cluster: Gram-positive bacteria with a low guanidine-cytosine (G+C) content
- Peptidoglycan-bound teichoic acids
- Non-sporulating, non-motile
- Sensitive to lysostaphin-A glycylglycine endopeptidase produced by Staphylococcus staphylolyticus that cleaves pentaglycine cross bridges found in staphylococcal peptidoglycan
- Un-encapsulated or limited capsule
What differentiates Staphylococci from Streptococci?
Catalase production:
•Present in staphylococci.
•Anti-phagocytic by converting H2O2 ⇒ H2O + O2
•Survive w/n eukaryotic phagocytic cells (neutrophils/macrophages).
What does coagulase production determine? Which staph is coagulase +? What are the 2 forms of coagulase? What is the function of each form?
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
What are the 3 coagulase-negative staphylococci? Which one is susceptible to Novobiocin? Which one is resistant to Novobiocin?
- S. epidermidis: Novobiocin-susceptible
- S. saprophyticus: Novobiocin-resistant
•#2 cause of UTI in sexually active young women
oNormal flora of genitourinary skin
oAffinity for uroepithelial cells - S. lugdunensis:
•Virulence similar to S.aureus
What are the 2 medically important staphylococci?
- S. epidermidis
2. S. aureus
What are the 6 identifying characteristics for S. epidermidis?
- Coagulase-negative
- Skin colonizer (common blood culture contaminant)
- Non-hemolytic, white colonies (i.e., no carotenoids)
- Non-mannitol fermenting
- Possess a capsule
- 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
What are the 8 identifying characteristics for S. aureus?
- Coagulase positive.
- Carotenoids cause pale golden yellow (Latin: “aurum”) pigmented colonies when grown aerobically at room temperature
- Grow rapidly under aerobic and facultatively anaerobic conditions
- β-hemolytic on sheep blood agar (complete hemolysis)
- Very adaptive to humans (resistant to drying, grow in 8.5% NaCl).
- Ferments mannitol
- Reservoirs:nasopharynx, perineum/groin
- Colonize skin and mucous membranes
•20% healthy people are persistent carriers
•30% are intermittent in any given individual
•50% are non-carriers
What are the cell wall components of S. aureus?
- Biofilm
- Polysaccharide capsule:
oTypes 5 and 8 (~75% isolates)
oAnti-phagocytic - Teichoic acids (TA):
oPolymers of ribitol phosphate
oMediates attachment to mucosal surface binding to fibronectin
oRole in inducing shock - Lipoteichoic acids (LTA):
oTriggers release of cytokines from macrophages and other cells
oDecorated with D-alanyl, repulse cationic antimicrobial peptides (CAPs)
What 6 features do S. aureus use to evade the immune system?
- Carotenoid pigment: resists oxidative burst killing (ROS) which help to survive in macrophages and phagocytes.
- Protein A: takes Fc portion of antibody and camouflages itself with the body’s own stuff.
- Clumping factor: makes it coagulase positive.
- Fibronectin-binding protein A: bind to mucous membranes.
- Capsule: prevent phagocytosis.
- Hemolysis: to get into cells.
What cytotoxin does S. aureus use?
α-hemolysin: creates a pore into host cells.
What enzymes does S. aureus use? What are they used for?
Used to take substrates from the host.
- Hyaluronidase: spreading factor, allows hyaluronic acid (component of connective tissue) to be degraded so that the organism can go thru.
- Coagulase: clotting or clot digestion. Engulfs itself in clot.
- Nuclease: break down DNA for energy.
- Staphopains: stimulate bradykinin (bring in blood supply).
What do superantigens do?
increase cytokine production
What are enterotoxins?
- “Pre-formed”
- Resist boiling, cooking, and gastric acid
- Target neural receptors in upper GI tract to stimulate vomiting center in brain
What is toxic shock syndrome toxin-1?
- Shares properties with enterotoxins
- Life-threatening.
- Usually localized with BP drop, and other out-of-proportion symptoms.
- Menstrual/non-menstrual`
What are exfoliatins?
- SSSS & bullous impetigo
- Protease cleaves desmoglein in epidermal desmosomes in strata granulosum of keratinized epidermis.
- Get shedding of skin in neonates.
- Localized = blisters.
