Streptococcus and Enterococcus

Question 1

What do Streptococcus spp. and Enterococcus look like?

Answer 1

they are gram-positive cocci (oval/round) typically found in chains

Question 2

Where are Streptococci and Enterococcus found?

Answer 2

they are normal flora of humans in the oral cavity, nasopharynx, and intestinal tract

Question 3

What are the characteristics of Streptococcus and Enterococcus?

Answer 3

most are facultative anaerobes, catalase negative (but Enterococcus may be weakly positive), non-motile, non-spore forming, group according to appearance of colonies and hemolytic reaction

Question 4

Alpha streptococci

Answer 4

produce alpha hemolysis, partial destruction of red blood cells around colony, looks green to brown

Question 5

Beta streptococci

Answer 5

produce beta hemolysis, red blood cells are completely lysed giving a clear colorless zone around the colony; streptolysin O and streptolysin S can be produced

Question 6

Gamma streptococci

Answer 6

no hemolysis, there is NO gamma hemolysis

Question 7

Which Streptococcus and Enterococcus are beta hemolytic?

Answer 7

Strep pyogenes, strep agalactiae, strep equisimilis, strep equi, strep anginosus, strep canis, (enterococcus, and streptococcus bovis are rarely beta-hemolytic)

Question 8

Which Streptococcus and Enterococcus are alpha hemolytic?

Answer 8

strep pneumoniae, strep bovis, enterococcus, viridans streptococcus group

Question 9

Which Streptococcus and Enterococcus are nonhemolytic?

Answer 9

strep bovis and enterococcus

Question 10

What are the virulence factors of S. pyogenes (group A)?

Answer 10

M protein - on cell wall surface allows organism to resist phagocytosis
Hyaluronidase - enzyme digests ground substance of CT
Streptokinase - enzyme digests fibrin clots
Streptolysin O - highly immunogenic, triggers auto-immune reaction

Question 11

What infections does S. pyogenes cause?

Answer 11

Pharyngitis, tonsillitis, swollen lymph nodes (“strep throat), otitis media, scarlet fever, impetigo, cellulitis

Question 12

Post-streptococcal sequelae

Answer 12

1) rheumatic fever - auto-immune reaction in heart muscle following pharyngitis with S. pyogenes
2) acute glomerulonephritis - auto-immune reaction in renal glomeruli following skin infection or pharyngitis with S. pyogenes

Question 13

What is the virulence factor of S. agalactiae (group B)?

Answer 13

produces polysaccharide capsules with 5 major antigen types

Question 14

What infections does S. agalactiae cause?

Answer 14

colonization of female genital tract (10-30%), leading cuase of meningitis, septicemia, pneumonia in neonates, urinary tract infections and bacteremia in the elderly and immunocompromised, post-surgical gynecologic infections

Question 15

What are the virulence factors of S. pneumoniae?

Answer 15

polysaccharide capsule that prevents phagocytosis, pneumolysin that is toxic to pulmonary endothelial cells and can spread to bloodstream

Question 16

What infections does S. pneumoniae cause?

Answer 16

virulent strains are encapsulated, more frequent cause of otitis media in children, community acquired bacterial pneumonia, meningitis, sinusitis

Question 17

What vaccines do we have to prevent S. pneumoniae infections?

Answer 17

Pneumococcal conjugate vaccine for infants and children, and 23-valent polysaccharide vaccine (23 PPVSV) for adults 65 +

Question 18

What does viridans Streptococcus look like?

Answer 18

it is green or alpha-hemolytic

Question 19

What infection does viridans Streptococcus cause?

Answer 19

most common cause of subacute bacterial endocarditis

Question 20

What are some characteristics of Enterococcus?

Answer 20

two species responsible for most human infections are E. faecalis and E. faecium, it has relatively low virulence, normal flora of intestinal tract

Question 21

What infections does the Enterococcus cause?

Answer 21

urinary tract infection, endocarditis, and wound infections

Question 22

What is Group D Streptococcus?

Answer 22

possible S. bovis group; can cause GI disease (carcinomas)

Question 23

How do we treat Streptococcus?

Answer 23

we use penicillin, but we can treat resistance with vancomycin or 3rd generation cephalosporin

Question 24

How do we treat Enterococcus?

Answer 24

it is resistant to penicillins and cephalosporins when given alone, so we use a combination of penicillin and aminoglycoside; if resistant to this combination we treat with vancomycin. If it is STILL resistant, we can use synercid or linezolid

Question 25

How do we identify Streptococci?

Answer 25

gram-stain: +
catalase: -
it can cause hemolysis, and we can use bacitracin sensitivity tests as well as rapid strep tests