Bugs
What are the morphological/general characteristics of Staphylococcus aureus?
What is...
cocci
cluster
gram positive
colonies are yellow/golden
facultative anaerobe
How does prevalence impact specificity, sensitivity, negative predictive value, and positive predictive value?
What is...
specificity/sensitivity = no change
PPV = direct relationship
NPV = inverse relationship
What is the difference between bacteriostatic and bactericidal?
What is...
Bacteriostatic slows growth
Bactericidal destroys bacteria
What do cytokines do and how does this relate to our patient's symptoms?
What is...
Activate nearby immune cells
Initiate inflammatory cascade
Recruit cells from circulation
Immunosuppressive
What is the function of histamine?
What is...
Increase inflammatory response
What is the difference between gram positive and negative bacteria in regards to staining?
What is...
Gram-positive = has thick peptidoglycan = call wall
Peptidoglycans retain crystal violet dye = stains purple
Define specificity and sensitivity in words and mathematically.
What is...
Sensitivity:
If pt is positive what is the likelihood the test will be positive
Sn = TP/(TP+FN)
Specificity:
If pt is negative what is the likelihood the test will be negative
Sp = TN/(TN+FP)
What is the mechanism of action of cephalexin and is it bacteriostatic/bactericidal??
What is...
Bactericidal = inhibits bacterial cell wall synthesis by binding penicillin-binding proteins
How do neutrophils/macrophages/dendritic cells recognize pathogens?
What is...
Neutrophil/macrophage/dendritic cells have pattern recognition receptors(PRR) which recognize Pathogen Associated Molecular Patterns(PAMPs) and Danger Associated Molecular Patterns(DAMPs)
Name 3 functions of normal flora of the skin.
What is...
Colonization resistance
Production of antimicrobial peptides/metabolites
Modulation of host immunity
Barrier function support
Name 3 test that can be used to identify Staphylococcus aureus. (explain the test and why it should be used)
What is...
Catalase test = catalase positive = can reduce reactive oxygen species
Beta hemolysis = completely lyse red blood cells = when grown on blood agar the colonies has a clear patch surrounding them
Mannitol salt agar = can grow in high salt environment
Coagulase positive = enzyme that converts fibrinogen to fibrin = clot formation
Define positive predictive value and negative predictive value in words and mathematically.
What is...
PPV:
If test is positive what is the likelihood the patient will be positive
PPV = TP/(TP+FP)
NPV:
If test is negative what is the likelihood the test will be negative
NPV = TN/(FN+TN)
What is the mechanism of action of diaminopyrimidines and are they bacteriostatic/bactericidal?
What is...
TMP inhibits dihydrofolate reductase
Explain complement
What is...
1. Activation via alternative/classical/lectin pathway
2. C3A/B cleavage -> C3A = inflammation C3B = opsonization/phagocytosis
3. C5A/CB cleavage -> C5A = inflammation C5B-9 = form Membrane Attack Complex(MAC) = lysis of microbe
What is cellulitis?
What is...
Inflammation of the deep dermis and surrounding subcutaneous tissue due to bacterial infection
Why is MRSA resistant and how is the resistance transferred?
What is...
mec gene on bacterial chromosome which codes for PBP-2A which has a lower affinity for beta-lactam antibiotics
between bacteria via transduction
What is a common sequential testing strategy?
What is...
Sensitive screening test followed by a more specific confirmatory test
What is the mechanism of action of sulfonamides and are they bacteriostatic/bactericidal?
What is...
SMX inhibits dihydropteroate synthase
Bacteriostatic alone
What are three abilities of a neutrophil?
What is...
1. Neutrophil Extracellular Traps(NETs)
2. Respiratory Burst
3. Degranulation = has granules = transport cytotoxic factors
How do Natural Killer Cells identify cells to kill and what three ways can they kill a cell?
What is...
Kills cells with downregulated MHC-1 receptors
Name 4 virulence factors of Staphylococcus aureus.
What is...
Cell wall = can bond to host cell and initiate infection
Coagulase = fibrin around bacteria can inhibit phagocytosis
Penicillinase = destroys penicillin
Protein A binds to Fc region of antibody = inhibits complement activation and phagocytosis
Capsule = decrease phagocytosis
Exotoxin = TSST-1 superantigen = upregulate MHC II-CD4+ receptor activity = uncontrolled inflammatory response
Leukocidin = lyses WBC
Exfoliatin = lyses epithelial cells
Lipases = lyses lipids
Calculate sensitivity, specificity, PPV, and NPV.
TP = 450
FP = 100
TN = 400
FN = 50
What is...
Sn = 90%
Sp = 80%
PPV = 81.8%
NPV = 88.9%
Why is cephalexin not ideal for gram negative bacteria and MRSA?
What is...
Gram negative bacteria have a lipopolysaccharide outer membrane and many produce beta-lactamase
MRSA has PBP-2A, beta-lactams cannot bind
Name two differences and similarities between macrophages and dendritic cells.
What is...
Differences:
1. Macrophages are tissue resident, dendritic cells are recruited to tissue
2. Dendritic cells activate naive T cells
Similarities:
1. Both derived from monocytes
2. Both can perform phagocytosis
What are the clinical presentation of cellulitis and how can you distinguish cellulitis and erysipelas?
What is...
Cellulitis:
Poorly demarcated erythematous area
Edema
Tenderness
Warmth
With/without purulent drainage
Erysipelas: