Strep

Question 1

General description

Answer 1

Gram +
Facultative anaerobic
Cocci in pairs
Mostly commensal

Question 2

3 schemes for identification

Answer 2

Hemolytic properties (alpha beta or gamma) - activity in blood agar

Lancefield groupings - serologic based on ex with antisera with cell wall carbohydrate antigens

Biochemical or physiologic properties
Further groups alpha

Question 3

Alpha hemolytic strep

Answer 3

Shows incomplete lysis

Greenish discolouration

Question 4

Beta hemolytic

Answer 4

Complete hemolysis

Question 5

Gamma streptococci

Answer 5

Non hemolytic so no lysis

Question 6

Under lancefield grouping A

Answer 6

Beta
GAS
Streptococcus pyogenes

Found in throats and skin

Pharyngitis cellulitis impetigo

Question 7

Lancefield Group B

Answer 7

Beta
Strep agalactiae

Causes neonatal sepsis n meningitis

Found in female genital tract

Question 8

Lancefield group D

Answer 8

Alpha

Enterococcus

Question 9

Impetigo

Answer 9

Lesions
Start as vesicles and then rupture and release serum

Has to be distinguished from herpes

Question 10

Lancefield C G

Answer 10

Beta hemolytic

Found in throat

Cause cellulitis (infx of dermis and subcutaneous tissue), bacteremia, endocarditis, pharyngitis

Question 11

Strep pneumoniae

Answer 11

Alpha hemolytic
Found in throats

Causes pneumonia meningitis endocarditis corneal n conjunctival infx

Question 12

Sequence of infection

Answer 12

Initial binding with surface binding proteins (lipotechoic n Fprotein)

Mediating internalization (w M protein - major virulence)

After internalization leads to
Persistence of infx - carrier state
Invasion of deeper tissues (aided by hyaluronidase)

Question 13

M protein

Answer 13

Activates coagulation in bacterial surface
Major virulence protein
Class 1 or 2

Is a type of adhesive that mediatates internalization of GAS by host

Terminal part of amino chain is highly variable
Strains that don’t express M are avirulent

Question 14

M protein is dominant in

Answer 14

Binding to keratinocytes on skin infx

Question 15

Protein g binds to

Answer 15

Fav part of antibodies

Prevents opsonization

Question 16

F protein

Answer 16

Binds fibronectin on host epithelial cell and favours adhesion

Critical in throats infx

Question 17

Streptolysin O

Answer 17

Oxygen labile
Destroys rbc, WBC, and platelets
Allows for hemolytic ability
Pore forming toxin

Question 18

Streptolysin S

Answer 18

Serum soluble
S means stable
Does beta hemolysis
Not antigenic

Question 19

Streptodornase

Answer 19

DNAse enzyme that depolarizers DNA

Question 20

Pyrogenic toxins

Answer 20

Found in few strains
Scarlett fever
Produce super antigens that stimulate T cell production to make streptococcal toxic shock syndrome

Question 21

Streptokinase and streptodornase are used for

Answer 21

Enzymatic debridement is necrotic tissues
Gives antibiotics better access

Are fibrinolysis so break up fibrin blood clots

Question 22

Pathology

Answer 22

Surface binding proteins bind epithelial fibronectin
Promotes high affinity binding and is first step in establishing infx
After adhering they invade cells

Question 23

Host response to group a

Answer 23

1. Complement coats strep
2. B cells make type specific opsonic antibodies against M protein
   (M is weakest link)
3. Antibodies bind
   4.Fc receptors on neutrophils bind antibody and induce phagocytosis
4. Type specific antibodies can be detected 4-8 weeks after infx

Question 24

Delayed antibody mediated diseases

Answer 24

Rheumatic fever

Glomerulonephritis

Question 25

4 types of disease due to exotoxin release

Answer 25

Pharyngitis
Scarlet fever
Skin infx
Toxic shock syndrome

Question 26

Strep pyogenes

Group a (GAS)
Beta hemolytic

Answer 26

20-40% cases of pharyngitis in kids
1-4day incubation
Symptoms normal sickness
Tonsils or throats issue

Question 27

Spread of GAS

Answer 27

Respiratory droplets

Short distance spread

Question 28

Scarlet fever symptoms

Answer 28

Strawberry tongue
Circumoral pallor around lips
Upper respiratory infx

Question 29

Step skin infx

Answer 29

Seen in poor hygiene conditions
Skin colonization plus trauma leads to impetigo
Lesions start as red papules eventually become honey comb like crusts

Erysipelas- bright red appearance of skin, forms plateau sharply demarcated from surrounding normal skin

Question 30

Acute rheumatocnfever

Answer 30

Caused by GAS
Mitral valve is affected then aortic valve

Fever
Myocarditis 
Joint swelling arthritis 
Chorea
Subcutaneous nodules 
Rash

Deals with M protein of strep

Question 31

Nephritogenic strain

Answer 31

Causes kidney damage
Get deposition of NaPlr in inner glomerular tuft
Causes endocapillary inflammation
Results in accumulation of immune complexes in outer side of glomerular tuft

Question 32

Glomerulonephritis

Answer 32

Seen 1-2 weeks after infx
Inflammatory disease of glomeruli
Seen after skin infx
Deposits of m protein in glomerulus induces antibody response

Question 33

Glomerulonephritis is characterized by

Answer 33

Edema
Hypertension
Hematuria
Proteinuria

Question 34

Group B - beta hemolytic a

Answer 34

b for baby

Strep agalactiae
Part of normal vaginal flora
Common in first week after birth

Avoid immune response by
Polysaccharide capsule
Makes c5a peptidase which inactivated chemoattractant c5a

Question 35

GBS manifestations

Answer 35

Neonatal sepsis, pneumonia, meningitis
Early onset infx occur within first week of life. High mortality rate

Late onset is 1week-3month
Get meningitis

Question 36

Ophthalmia neonatrium

Answer 36

Conjunctivitis in the first month of life

Incident is 1.6-12%