Streptococci

Question 1

Characteristics of Streptococci

Answer 1

• facultative anaerobes
• Catalase negative
• normal members of body flora
• non motile
• non spore forming

Question 2

Growth medium of streptococci

Answer 2

Blood agar

Question 3

Hemolysis on blood agar

Answer 3

Alpha hemolytic -> incomplete hemolysis (oxidizes haemoglobin to biliverdin) -> greenish discoloration

Beta hemolytic -> complete hemolysis -> clear zone (no RBC, we only see the agar)

Gamma (non) hemolysis -> some bacteria grow, but no change in RBC

Question 4

Structure of Streptococcal cell from inside to outside

Answer 4

• cytoplasmic membrane
• peptidoglycan
• group carbohydrate
• protein antigens
• capsule

Question 5

Serologic classification is based on

Answer 5

Antigenic differences in cell wall carbohydrates
(-> in beta hemolytic streptococci)

Question 6

Which streptococci has no group specific antigen?

Answer 6

Viridans streptococci & s. Pneumonia

Question 7

Who is the most important human pathogen in Group A Streptococci?

Answer 7

S. Pyogenes

Question 8

Susceptibility of s. Pyogenes to

Answer 8

Bacitracin

Question 9

S. Pyogenes causes disease by three mechanisms

Answer 9

• pyogenic inflammation
• exotoxin production
• immunologic

Question 10

Name the virulence factors of s. Pyogenes

Answer 10

• capsular polysaccharide -> hyaluronic acid
• M Protein -> inhibits alternate C pathway, opsonization, phagocytosis
• Lipoteichoic acid -> cytotoxic
• protein F -> binds fibronectin (attachment)
• protein G -> binds Fc portion of ABs

Question 11

Enzymes in S. pyogenes

Answer 11

• streptokinase (digests fibrin clots)
• nuclease
• hyaluronidase
• proteinase

Question 12

Exotoxins of s. Pyogenes

Answer 12

Streptolysins
Streptococcal pyrogenic exotoxins

Question 13

Suppurative diseases of S. pyogenes

Answer 13

• pharyngitis
• scarlet fever (strawberry tongue)
• cutaneous & soft tissue infection (Impetigo, Erysipelas, necrotizing fascitis)
• systemic diseases (Toxic schock syndrome)

Question 14

S. Pyogenes appearance on blood agar

Answer 14

Small colony, large zone of hemolysis

Question 15

Member of group B Streptococci

Answer 15

S. Agalactiae

Question 16

How does S. agalactiae reacts to bacitracin?

Answer 16

Resistant

Question 17

Virulence factors of S. agalactiae

Answer 17

• polysaccharide capsule
• beta hemolysin
• C5a peptidase

Question 18

Which test is used to detect s. Agalactiae?

Answer 18

CAMP test

Question 19

Which test is done?

Answer 19

CAMP test -> s. Agalactiae

Question 20

Infections of S. agalactiae common in ?

Answer 20

Pregnant & newborn infants or adults
-> pneumonia, sepsis, meningitis

Question 21

Hippurase test is positive in which bacteria?

Answer 21

S. Agalactiae

Question 22

Group D streptococci member

Answer 22

S. Bovis

Question 23

S. Bovis can cause

Answer 23

Bacteremia
Abdominal abscesses (associated with carcinoma of colon)
Wound infections

Question 24

Group D enterococci

Answer 24

Enterococcus faecalis

Question 25

Lab identification of Enterococci

Answer 25

Black colonies on bile esculin agar

Question 26

Enterococci treatment

Answer 26

Intrinsic resistance to cephalosporins
Inhibited but not killed by penicillin -> combined with aminoglycosides for invasive infections

Question 27

Characteristics of S. pneumonia

Answer 27

• diplococci
• encapsulated

Question 28

Virulence factors of S. pneumonia

Answer 28

• capsule
• pneumolysin O
• leukocidin
• neuraminidase
• hyaluronidase
• IgA protease

Question 29

S. Pneumoniae infections

Answer 29

Pneumonia
Meningitis
Otitis media

Question 30

How to differentiate S pneumonia from other alpha hemolytic streptococci?

Answer 30

S pneumoniae is Optochin sensitive

Question 31

Answer 31

Optochin test