streptococci

Question 1

how do you know if an infection is streptococcus?

Answer 1

• gram positive
• chains

Question 2

how do you further differenciate streptococcus?

Answer 2

• haemolysis on blood agar
• beta - antigenic group
• alpha - optochin test

Question 3

outline how haemolysis on blood agar is used to differentiate streptococci.

Answer 3

Beta - complete lysis (clean zone appears around the colonies) - because of pore forming toxins

alpha - partial lysis - (green discolouration surrounding the colonies) - because of production of hydrogen peroxide

gamma - no lysis occurs - colonies dont change the colour of the agar

Question 4

if the streptococci is beta on blood agar, how do we further differentiate this?

Answer 4

• Lancefield A-H and K-V (most important and A and B)
• this is based on their antigen (carbohydrate) on its surface
• antiserum is added to each group is added to the bacteria - clumping indicated recognition

Question 5

outline the most relevant group A and group B strep?

Answer 5

group A - S. pyogenes
group B - S. apalactiae

Question 6

outline the virulence factors of S. pyogenes.

Answer 6

exported factors
toxins
surface factors

exported factors:
- hyaluronidase - spreading
- streptokinase - breaks down clots
- C5a peptidase - reduces chemotaxis

toxins:
- streptolysins O&S - binds cholesterol
- erythrogenic toxin - exaggerated response

surface factors:
- capsule - hylauronic acid
- M protein on surface - encourages compliment degredtion

Question 7

what infections are caused by S. pyogenes?

Answer 7

• would infections - cellulitis and puerperal fever
• tonsilitis and pharyngitis
• otitis media
• impetigo
• scarlet fever

complications:
- rheumatic fever
- glomerulonephritis

Question 8

what infections do S. agalactiae commonly cause?

Answer 8

neonatal infection

Question 9

how do we further classify alpha haemolytic strep?

Answer 9

optochin test
- resistant
- sensitive - S. pheumoniae

Question 10

name the predisposing factors of S. pneumoniae infections and the conditions which the bacteria cause.

Answer 10

normal commensal in oro-pharynx - 30% of population

causes:
- pneumonia
- otis media
- sinusitis
- meningitis

predisposing factors:
- impared mucus trapping
- hypo-gamma-globulin-aemia
- asplenia

Question 11

outline the virulence factors of S. pneumoniae.

Answer 11

• its capsule has 84 diff types of serogroup - hard to vaccinate
• antipathogenic - evasion from phagocytosis
• inflammatory wall constituents
• contains the cytoxin pneumolysin - pore forming toxin

Question 12

whats another term for optochin test resistant strep?

Answer 12

viridans strep

Question 13

what group of haemolytic can virdans strep be?

Answer 13

alpha or none-haemolytic

Question 14

outline the main points of virdans group strep.

Answer 14

• can cause dental absecess
• S. sanguinis and S. oralis - can cause infective endocarditis
• can cause deep organ absesses
• most virulent are the milleri group

Question 15

name the main beta-haemolytic strep.

Answer 15

• group A - S. pyogenes
• group B - S. agalactiae (neonatal infections)

Question 16

name the main alpha haemolytic strep.

Answer 16

sensitive - S. pneumoniae
resistant - virdans group strep