Week 1 Day 2 Flashcards
Two common gram positive cocci?
Strep and staph
What is the catalase enzyme and test?
Enzyme that takes H2O2 and turns it into H2O and O2
If a bacteria bubble during a catalase test it is positive.
Which one strep or staph is catalase negative?
Strep
Two different ways Strep are categorized?
Hemolysis and the Lancefield Classification System
What is the hemolysis test and results?
Test to see bacteria’s ability to lyse red blood vessels
Alpha= partial brown or green opaque around colony
Beta= complete- clear in colony areas
Gamma= no change
What is the Lancefield Classification System?
a system of classification that classifies catalase-negative Gram-positive cocci based on the carbohydrate composition of bacterial antigens found on their cell walls created to categorize strep into Groups A-D
Now there are strep that don’t fit into the system
What is a major pathogenic strep and what Lancefield group?
Group A and S. pyogenes aka G.A.S.
S. p. is the most common group A and often referred to synonymously
Name 2 alpha hemolytic strep species and a few things about each of them?
S. pneumoniae- optochin sensitive, capsule and Quellung pos
S Viridians-optochin resistant, no capsule, Quellung neg
Name 2 beta hemolytic strep species and a few things about each of them?
S. pyogenes- Group A, bacitracin sensitive
S. agalactiae- Group B, bacitracin resistant
Name 2 gamma hemolytic strep species and a few things about each of them?
Enterococcus- bile esculin pos, 6.5% NaCl growth
non-Enterococcus- Group D, bile esculin pos, 6.5% NaCl no growth
Name two examples of GAS virulence factors for evasion?
M-protein- protein on cell surface that resists phagocytosis
Streptolysins O and S- hemolytic exotoxins released that are toxic to neutrophils, RBCs and platelets
Name 2 GAS virulence factors for Invasion?
Streptokinase- activates plasmin, dissolves blood clots to release additional bacteria
Hyaluronidase- breaks down hyaluronic acid in connective tissue
What is the GAS virulence factor that is also what is looked for in the strep test?
Little bit about it?
Streptolysin O- triggers immune response,
O2 labile
What is another group of strep virulence factor exotoxins?
Pyrogenic exotoxins
Such as erythrogenic toxin as in Scarlet fever
Or Superantigens that stimulate Tcells and cause toxic shock syndrome
What causes Scarlet fever?
GAS- associated with GAS pharyngitis
Erythrogenic toxin
Symptoms of scarlet fever?
Head/trunk/extremities have a sandpaper rash that desquamates aka peels
Circumoral pallor
Strawberry tongue
There is also a benign course where it is mild
4 skin and soft tissue infections of GAS that are suppurative aka cause pus or exudate?
Impetigo, folliculitis
Necrotizing fasciitis
Cellulitis- dermis and subcutaneous infection
Erysipelas- epidermis only rash fever
S pyogenes aka GAS Impetigo is common in what age?
2-5 yrs old
Symptoms of GAS impetigo/pyoderma?
Ulceration of skin/ crusted lesions usually on face
Is GAS impetigo/pyoderma contagious?
Yes
GAS impetigo/pyoderma treatment?
Local/mupirocin or penicillin
Potential complication of S pyogenes Impetigo?
Post Streptococcal Glomerulonephritis
Post Streptococcal Glomerulonephritis?
Sometimes Follows skin and pharyngeal infections
More common in kids
Dark urine from hematuria, edema and hypertension from fluid retention
Not helped with antibiotics but usually goes away on its own
What virulence factors are associated with necrotizing fasciitis and what do they do?
Exotoxins SpeA and SpeC- activate T-Cells and stimulate inflammatory cytokines
Cysteine protease SpeB degrades extra cellular matrix, cytokines, lgs
