Lec 5: Agents of Skin Infection I (O'Brien)

Question 1

Alpha hemolysis

Answer 1

Partial blood lysis; hemoglobin leaks out, which leads to a green color on blood-agar plates

Question 2

Beta hemolysis

Answer 2

Complete blood lysis and heme degradation; produces clear zone around bacterial colony on blood-agar plates

Question 3

Gamma hemolysis

Answer 3

No hemolysis; aka nonhemolysis

Question 4

Group A Streptococci

Answer 4

Species: S. pyogenes
Hemolysis: Beta
Gram (+) and forms in chains
Diseases: Pharyngitis, soft tissue infection, toxic shock syndrome, necrotizing fasciitis, acute rheumatic fever, etc
Carbohydrate Group A (Lancefield)

Question 5

M Protein

Answer 5

Major virulence factor for GAS
In Group A Streptococci; anti-phagocytic, adhesin to keratinocytes, attached to cell wall of GAS (Group A Strep), outermost regions are variable in structure
Some M proteins appear similar to host proteins, so cannot use these as vaccine targets and an adaptive immune response to some M proteins may lead to autoimmune disorders

Question 6

Impetigo

Answer 6

Superficial bacterial infection of the skin, leaves crusty, honey-colored lesions; epidermis alone involved
Commonly seen during warm, moist weather
Associated with s. Aureus and s. Pyogenes

Question 7

Hyaluronic Acid Capsule

Answer 7

Disguise for the bacteria since HA is common in humans, antiphagocytic

Question 8

Scarlet Fever

Answer 8

Rash on body coming from pharyngeal infections, caused by bacterial toxins: Streptococcal pyrogenic exotoxins A, B, and C. A and C are superantigens capable of inducing strep toxic shock syndrome
Signs: Circumoral redness, strawberry tongue, desquamation post-rash

Question 9

Sequelae

Answer 9

Secondary effects, like a disease caused by a preceding disease (ex: acute rheumatic fever)

Question 10

Acute Rheumatic Fever

Answer 10

Non-suppurative sequela to strep pharyngitis, cause of valvular heart disease, appears 1 to 4 weeks after pharyngitis
Manifestations: Carditis, polyarthritis, chorea (uncontrolled dancing movements), etc. Thought to be an autoimmune disease
Requires long term treatment with Penicillin to prevent future GAS infections

Question 11

Suppurative

Answer 11

Pus-forming

Question 12

Acute Poststreptococcal Glomerulonephritis

Answer 12

Occurs 1-4 weeks post strep infection; Caused by only a few M-protein Types, pathogenesis suspected to be immune complex formation at glomeruli, leading to complement activation and degradation.
Manifestations: Blood and elevated protein in urine

Question 13

Erysipelas

Answer 13

Skin infection causing a raised, bright red patch with sharp edges, dermal lymph tissue involved, commonly on the face
May spread quickly and is dangerous if not treated with Penicillin

Question 14

Myositis/Necrotizing Fasciitis

Answer 14

Potentially lethal infections of muscle (deep), requires aggressive IV therapy

Question 15

Rapid Strep Test

Answer 15

Very specific, NOT sensitive, strep ruled out when negative test appears. Detects Group A carbohydrate antigen from bacteria

Question 16

Group B Strep

Answer 16

Species: S. agalactiae
Hemolysis: Beta and Gamma
Diseases: Neonatal meningitis and sepsis
Neonates at high risk, pregnant women screen for GBS before birth
Uses polysaccharide capsule for evasion of opsonization and phagocytosis
Gram (+) and forms in chains
Carbohydrate Group B Antigen

Question 17

Soft Tissue Infections:
Exogenous
Endogenous
Toxin-Mediated

Answer 17

Exo - direct invasion of microbe from external environment
Endo - invasion of microbe from internal environment
Toxin - manifestations at sites away from infected area

Question 18

Cellulitis

Answer 18

Subcutaneous fat layer infection

Question 19

All Streptococci are:

Answer 19

Gram Positive

Catalase Negative

Question 20

Hyalouronidase

Answer 20

AKA Spreading Factor, helps bacteria spread by breaking down Hyaluronic Acid in the ECM (made by S. Aureus and S. pyogenes)

Question 21

Abscess Formations (the 3 types)

Answer 21

Folliculitis (hair follicles), Furuncles (boils), Carbuncles (large boil/series of boils)

Question 22

Necrotizing Infections

Answer 22

Fasciitis and gas gangrene (caused by Clostridium genus)

Question 23

Diseases of Staphylococci

Answer 23

Folliculitis, Carbuncles, Furuncles, Impetigo, Cellulitis

Question 24

Diseases of Streptococci

Answer 24

Impetigo, Erysipelas. Lymphangitis, Cellulitis, Synergistic Cellulitis, Necrotizing Fasciitis

Question 25

Superantigen Toxins

Answer 25

A toxin released by bacteria which cross-links the T-Cell Receptor and MHC Class II molecules, causing massive cytokine release from T Helper Cells and Macrophages

Question 26

PANDAS

Answer 26

Pediatric Autoimmune Neuropsychiatric Disorder Associated with group A Streptococci
Five Criteria
1) OCD or tic disorder
2) Pediatric Onset
3) Abrupt onset, episodic course of symptoms
4) Association with GAS infections
5) Association with neurologic abnormalities (tics, motoric hyperactivity (excessive movement), choreiform movements (jerky involuntary movements across whole body)

Question 27

Penicillin G

Answer 27

Drug of choice for GAS infections

Question 28

Resident vs. Transient Skin Flora

Answer 28

Resident - long-term bacteria on host, typically not pathogenic
Transient - short-lived bacteria on host, can be pathogenic (S. aureus and S. pyogenes)

Question 29

PYR Test

Answer 29

Pyrrolidonyl Arylamidase Test
If you already know your culture is streptococcus, you may use this test to determine if it is GAS or not.
(+) = GAS (colony turns red)