Streptococci and Enterococci

Question 1

Streptococcus pyogenes

Answer 1

Group A strep, Beta hemolytic

Question 2

Streptococcus agalactiae

Answer 2

Group B strep, Beta hemolytic

Question 3

Appearance of streptococci

Answer 3

Gram positive in chains

Question 4

Beta hemolysis

Answer 4

Blood agar plate turns clear where the strep is spread

Question 5

Alpha hemolysis

Answer 5

Green

Question 6

Gamma hemolysis

Answer 6

Clear

Question 7

Lancefield typing

Answer 7

Uses an antibody test to look for clumping. Positive test shows clumping, negative test does not.

Question 8

Group A beta-hemolytic streptococci and major virulence factor

Answer 8

S. pyogenes, sensitive to bacitracin (which is what determines group A). M protein

Question 9

Pathogenesis of Strep A infection

Answer 9

Suppurative complication: sore throat, primarily neutrophil responses
Non-suppurative complications: manifestations of disease remote from primary site of colonization/infection.

Question 10

Four suppurative (pyogenic) complications of S. pyogenes (group A beta-hemolytic)

Answer 10

Pharyngitis, impetigo, cellulitis, necrotizing fasciitis

Question 11

Four non-suppurative complications of S. pyogenes

Answer 11

Acute rheumatic fever, poststreptococcal glomerulonephritis (THESE ARE BOTH Immunogenic), scarlet fever, streptococcal toxic shock syndrome.

Question 12

Acute Rheumatic Fever

Answer 12

Occurs from ages 6-20, common in impoverished countries. Clear association with preceding throat S. pyogenes infection (not any other area). Higher incidence if strain has high levels of M-protein.

Question 13

Why does the heart get messed up in ARF?

Answer 13

Molecular mimickry, cross reactivity of GAS antibodies with that of the endocardium.

Question 14

Clinical manifestations of ARF

Answer 14

Migratory arthritis, carditis, sydenham’s chorea, erythema marginatum.

Question 15

Why is childhood strep treated so aggressively?

Answer 15

To prevent progression into rheumatic fever.

Question 16

Post-streptococcal glomerulonephritis

Answer 16

Antibodies and complement components react with streptococcal antigens to form immune complexes, which deposit in glomerulus.

Question 17

Clinical manifestations of PSG

Answer 17

Affects children, hypertension, edema, bloody urine, may be associated with development of hypertension later in life.

Question 18

Toxic shock syndrome

Answer 18

Caused by so-called pyrogenic exotoxins (SPEA, SPEB, SPEC), act as superantigens that nonspecifically bind MHC and T cells causing cytokine storm. Shock and multi-system organ failure ensue.

Question 19

Streptococcus Agalactiae

Answer 19

Group B beta hemolytic strep (not sensitive to bacitracin). Associated with neonatal and puerpural sepsis, occasionally UTI and endocarditis too.

Question 20

Enterococcus Fecalis, Enterococcus faecium

Answer 20

Bowel organisms, cause infections below the diaphragm, relatively antibiotic-resistant particularly to cephalosporins and other beta lactams. Urinary tract infections, peritonitis.

Question 21

What differentiates enterococci from other streps?

Answer 21

Relatively antibiotic-resistant particularly to cephalosporins and other beta lactams.

Question 22

Strep Viridans

Answer 22

Alpha-hemolytic streps (green=viridans), include S. mutans (dental caries), S. sanguis (endocarditis on previously damaged valves). Not sensitive to optochin like pneumococci are.

Question 23

How to distinguish pneumococci from strep viridans?

Answer 23

Optochin test. Strep viridans is not sensitive to optochin, but pneumococci are.

Question 24

Do strep viridans invade?

Answer 24

No, but can pass into bloodstream when gums are damaged. Can cause endocarditis.