2.2

Question 1

Blood agar

Answer 1

• A nutritious solid culture medium containing 5% intact mammalian red blood cells, usually sheep or horse
  ○ Bacteria, when inoculated into an agar plate, will grow to form colonies
  ○ Some bacteria produce haemolysins - substances which digest red blood cells
  ○ These haemolysins diffuse from the colonies out into the agar

Question 2

• Beta haemolysis

Answer 2

○ Some haemolysins completely digest the red blood cells in the agar, producing complete haemolysis, a transparent zone of agar surrounding each colony

Question 3

• Alpha haemolysis

Answer 3

○ Partially digest the red blood cells, leaving an olive green colouration of the agar around each colony
○ Sometimes called viridans streptococci due to the green colour

Question 4

viridans streptococci

Answer 4

alpha haemolytic

Question 5

B-haemolytic streptococci classified by

Answer 5

• Using the Lancefeild classification system streptococci can be grouped into 20 serotypes

Question 6

lancefeild classfication system

Answer 6

• In the lap, beta haemolytic strep is mixed with individual Lancefeild antisera
  ○ latex particles coated with antibodies against the individual carbohydrate antigens
  ○ Check which antisera the streptococcal bacteria agglutinates with

Question 7

lancefeild group A

Answer 7

• Streptococcus pyogenes

Question 8

lancefeild group B

Answer 8

streptococcus agalactiae

Question 9

one Alpha haemolytic streptococci

Answer 9

Streptococci pneumoniae

Question 10

alpha haemolytic strep characteristics

Answer 10

• Many of these streptococci are part of the normal flora of the oropharynx, gastrointestinal tract and vagina
  
  • May become pathogens when they gain access to sites in the body where they don’t belong

Question 11

Streptococci pneumoniae

Answer 11

○ Highly virulent
○ May also be commensal of the human nasopharynx
○ Virulence factor - polysaccharide capsule
○ >90 serotypes based on antigenic differences in the capsule
○ Appears as a diplococcus

Question 12

2 enterococci

Answer 12

E. Faecalis

E. Faecium

Question 13

enterococci serotype with

Answer 13

group D antigen

Question 14

enterococci morphology

Answer 14

gram positive cocci in short chains

Question 15

enterocci are commensals of

Answer 15

the human bowel