General comment

Gram-Stain

MacConkey agar

Blood agar

Bacterium

Shape

Reaction

LF/NLF

Growth

Haemolysis

Colony

Hazy haemolysis along streak line often before small colonies can be seen. Very pleomorphic in the gram-stained smear. catalase

R(C)

+

 

-

+

(hazy)

Translucent, pin-point 0.5mm

    Actinomyces  pyogenes

The size of the clear zone of haemolysis varies with the lancefield group and species. Catalase

C

+

 

-

+

Translucent, glistening and round 0.5-1.0mm

  Betahaemolytic

  streptococci

Colonies very similar to the beta-haemolytic streptococci. Young colonies yield many coccal cells. Catalase+

R(C)

+

 

-

+

White, smooth and round 0.5-1.0mm

   Listeria     monocytogenes