7 Flashcards
The genus Staphylococcus
Gram + cocci – Non-‐mo6le – Non-‐spore forming
– Predominantly faculta6ve anaerobes
– 42 valid species
• 10 have subspecies
Catalase Test +
Ability to grow in 7.5% H2O2
Catalase nega6ves
other genuses
• Streptococcus
• Enterococcus
The coagulase test
Differen6ates S. aureus and 6 other species from among 42 total species
• S. aureus causes the highest burden of disease in people
Spectrum of disease
S. aureus is most common causa6ve agent
• Integumentary and wounds • Bacteremia -‐> – Organ abscesses – Endocardi6s – Embolic pneumonia – Sep6c arthri6s • Aspira6on pneumonia • UTI • Toxic shock syndrome • Scalded skin syndrome Food poisoning
Encounter
Live on and around people – 30%-‐40% prevalence nasal
carriage
• Muco-‐cutaneous junc6ons
• Skin, mucosal surfaces
• Hearty environmental survival – Clothing, surfaces
• Usually behave commensally
(Opportunis6c in right condi6ons)
Mul6plica6on/Spread
Variable with – Bacterial inoculum (more is worse) – Host immunocompetence – Loca6on of infec6on • Bacteremia + immune compromise = trouble
MSCRAMMs
Microbial Surface Components Recognizing Adhesive Matrix Molecules”
Fibronec6n
binding proteins (FnbpA and FnbpB)
Fibronec6n is a key player in the extracellular matrix func6on of adhesion
More MSCRAMMs
– Collagen binding protein (CNA)
• Car6lage, connec6ve 6ssue, bones, joints
– Clumping factors bind fibrinogen • Important in clot forma6on
• Responsible for + coagulase test in vitro • Key in pathogenesis of endocardi6s
Acute suppura6ve inflamma6on
accumulation of pus
PMNS
Polymorphonuclear WBCs or “PMNs”)
PMNs
first to show up
Phagocytosis of foreign invaders
• Release toxic oxida6ve substances to try to kill
bacteria: “ROS” Reac6ve oxygen species
• Release signaling molecules to call more WBCs to the area (cytokines)
Virulence factors of S. aureus complicate
ma]ers
– Polysaccaride capsule
– Protein A
– Pore-‐forming toxins
Panton-‐Valen6ne Leukocidin
very toxic to PMNs
– Polysaccaride capsule
blocks phagocytosis
– Protein A
blocks an6body func6on
Pore-‐forming toxins
pop PMNs and other cells leading to more damage and inflamma6on
SSSS
Staphylcoccal Scalded Skin Syndrome
– Exfolia6ve toxins A & B.
Toxins cause the layers of the epidermis to separate
Exfolia6ve toxins are proteases with high-‐specificity for desmosomal proteins in the skin
Toxic Shock Syndrome
9 YO girl presents with arthralgia, myalgia
– Quickly progressed to sep6c shock and renal failure.
• Cause: An oral abscess infected with TSST-‐1 producing S. aureus
TSST-‐1 is a superan6gen
- Superan6gens cause an unregulated inflammatory response by ac6va6ng high #s of CD4+ T cells
- Cross link T-‐cell receptor with the MHC-‐II surface molecule of an6gen presen6ng cells (e.g. macrophages)
Staphylococcal Food Poisoning
not infection, infestation.
Many strains of S. aureus secrete enterotoxins.
EnterotoxinsA,B,C,D,E
– Superan6gens,Causeintenseperistalsis
– Heatstable:Cookingfoodwillkillthebacteria, but not the toxin that they have formed.
β-‐lactam an6microbial agents are inhibitory substrates for PBPs
Penicillins • Semi-‐synthe6c penicillins • Cephalosporins • Carbapenems • Monobactams Cephalosporin Penicillin
