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48 Cards in this Set
- Front
- Back
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What is the 2nd leading cause of bacterial UTI?
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S. saprophyticus
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What is Staph aureus' status in terms of Gram stain, coagulase, mannitol fermentation, NaCl susceptibility, and pigmentation production?
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S. aureus is Gram+, coagulase+, mannitol fermenting, NaCl resistant, and produces golden/yellow pigment
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What percent of human population colonized in nares by S. aureus?
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~30%
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Which Staph spp. commonly causes biofilm infections of indwelling devices?
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S. epidermidis
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What are the 3 pathenogenic Staph spp.?
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S. aureus, S. epidermidis, S. saprophyticus
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What is the pathophysiology of folliculitis?
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S. aureus invades the pilosebaceous units in the skin resulting in inflammation.
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What is sycosis barbae?
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Barber's itch which is S. aureus folliculitis on the face of bearded men.
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What organism(s) cause imeptigo?
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S. pyogenes (GAS), S. aureus, or a combination of both
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How does GAS differ from S. aureus impetigo in progression?
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GAS begins on skin and goes to nasal passages while S. aureus is the opposite.
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How is bullous differentiated from non-bullous impetigo?
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Bullous exhibits intraepidermal vesicles forming bullae filled with pus and Nikolsky's sign-caused only by S. aureus expressing exfoliative toxins ETA or ETB.
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What is Nikolsky's sign?
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Desquamation of skin with gentle rubbing.
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What is Ritter's Disease?
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Also known as Staph Scalded Slkin Syndrome and Pemphigus neonatorum. Caused by staph toxins ETA (prophage) and ETB (plasmid). Results in desquamation of corneal epithelium.
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What is the mechanism of action of ETA/ETB?
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These toxins are serine proteases that target desmoglein-1, a desmosomal cadherin required for cell-cell contact in the corneal layer of epidermis.
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What is mastitis?
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Tenderness in one breast sometimes accompanied by fever indicating S. aureus infection.
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What is erysipelas?
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Superficial celllulitis with "peau d'orange" (orange peel skin) appearance caused by S. aureus.
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What is cellulitis?
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An invasive, deep tissue infection that is painful caused by S. aureus.
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What is necrotizing fasciitis?
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The most severe skin condition caused by S. pyogenes and sometimes S. aureus (usually MRSA). Requires immediate action.
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What is toxic shock syndrome?
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S. aureus makes toxic shock syndrome toxin 1 (TSST-1), a superantigen, that binds T-cells leading to a cytokine storm. Causes fever, hypotension, organ failure, and maculopapular rash with desquamation.
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What is menstrual toxic shock syndrome?
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Women using tampons sometimes get TSS because of optimal conditions (intermediate O2, high CO2, high protein).
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What is leading cause of food poisoning in U.S.?
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Salmonella
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What is 2nd leading cause of food poisoning in U.S.?
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Production of heat stable enterotoxins (15 total - SEA-SEU) by S. aureus.
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What is endocarditis?
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Progression of bacteremia to heart valves, chamber walls, or septae. Native form caused by oral strep and S. aureus. Prosthetic form is S. epidermidis.
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What causes S. aureus pneumonia?
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Infection from S. aureus subsequent to viral Influenza which can progress to necrotizing pneumonia (esp. with MRSA).
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Why are CF patients particularly susceptible to S. aureus pneumonia?
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They have chronic S. aureus infection accompanied by antibiotic therapy that provides environment for resistant organisms to develop.
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What are Small Colony Variants (SCV's) and how do they differ from normal S. aureus?
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SCV's are slow growing, non-pigment producing, non-hemolytic variants of S. aureus exhibiting drug resistance due to mutations arising from antibiotic therapy.
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What are 2 types of drugs that SCV's are tolerant of?
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Aminoglycosides and trimethoprim/sulfonamide drugs.
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What is acute and chronic osteomyelitis?
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S. aureus infects long bones in children and vertebrae in adults in acute osteomyelitis. In chronic form, SCV's can develop and persist within osteoblasts.
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What is the most common cause of septic arthritis in chidren?
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S. aureus
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What is are the two most common causes of septic arthritis in adults?
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1) N. gonorrhoeae and 2) S. aureus
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What is bursitis?
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S. aureus infection of periarticular bursa that becomes inflamed and swollen.
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List the S. aureus exotoxins.
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alpha toxin, beta toxin, gamma toxin, delta toxin, phenol soluble modulins, pyrogenic superantigens (TSST-1), and ETA/ETB.
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What is alpha toxin?
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A cytolytic pore-forming toxin responsible for alpha-hemolysis which induces cell lysis in vivo.
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What is beta toxin?
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A sphingomyelinase which causes cold-induced erythrocyte hemolysis.
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What is gamma toxin?
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A leukocidin (neutrophil lysing) toxin composed of S and F subunits present in most Staph organisms. (G's in SF, CA)
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What is delta toxin?
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A small protein that lyses various cells and organelles.
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What are phenol soluble modulins?
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They are structurally related to delta toxin that form amphipathic helices and facilitate membrane pore formation
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What Staph exotoxins cause food poisoning?
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The superantigen pyrogenic exterotoxins (SEA-SEU).
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What cytokines are released following superantigen activation of T cells?
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IL-1, IL-2, TNF-alpha, and gamma interferon.
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Describe the S. aureus sortases.
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SrtA and SrtB are enzymes that generate a peptide bond in an uncrosslinked portion of the peptidoglycan layer in Staph. This helps mediate cell wall anchoring.
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What is S. aureus protein A (spa)?
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An SrtA-anchored IgG binding protein which prevents opsonization via the classical pathway.
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What is S. aureus collagen binding protein (cna)?
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A surface protein that mediates binding to extracellular matrix, esp. important in osteomyelitis.
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What is Staph fibrinogen/fibronectin binding protein?
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Can convert fibrinogen to fibrin and bind tissue fibronectin. Important for ability to cause endocarditis.
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What are S. aureus Isd's?
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Important for Heme-Iron acquisition. IsdH binds haptoglobin, IsdB binds hemoglobin. IsdG/I free Iron from heme.
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What is Lipoteichoic Acid?
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Gram+ equivalent to LPS, recognized by TLR-2. Mediates adherence to heart valve endothelium.
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What is the function of Staph capsular polysaccharides?
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Prevent non-antibody mediated opsonization but hinders ability to cause endocarditis.
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What are Staph Chromosome Cassettes?
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Mobile genetic elements encoding mecA methicillin resistance (PBP2a protein).
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How do beta-lactam antibiotics work?
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They mimic the D-Ala-D-Ala terminal peptide of terminal peptide on NAM and bind to transpeptidase domains of PBPs (bactericidal).
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What do methicillin/oxicillin offer than penicillin does not?
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They are beta-lactamase resistant beta lactams but do not work on MRSA which have alternate PBP's.
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