Systematic Veterinary Bacteriology and Mycology

CULTURAL CHARACTERS

• The organism grows on media containing blood, serum and produces small dewdrop like colonies on the surface of the media.
• Streptococci produce three zones of Haemolysis on blood agar.
  • a - Haemolysis: A zone of greening or of partial haemolysis eg: S. pneumoniae produces a - haemolysis and mucoid type of colonies on sheep blood agar.Immediately around the colonies there are remains of RBC and green colouration (breakdown of Haemoglobin to the intermediate stage methaemoglobin) . This is surrounded by a narrow second zone of complete haemolysis.
  • b - Haemolysis: A clear zone of haemolysis around the colony eg: S. equi. It is a defined zone of complete lysis of both RBC and Haemoglobin.
  • g - Haemolysis: No alteration of either RBC or Haemoglobin
• Edward's medium which contains thallous acetate and crystal violet favours the growth of Streptococcus.
• The presence of aesculin helps in identifying group D Streptococci from Streptococcus agalactiae. S. agalactiae forms small transparent, bluish grey color colonies. S. dysgalactiae forms green colonies. S. uberis is esculin positive, causing brown discolouration of the medium and brown (dark) colonies.

Biochemical properties of Streptococci

• Distinguishing features of Streptococci causing Bovine mastitis.

Organism	Sugar fermentation			Sodium hippurate test	CAMP test
	Salicin	Inulin	Sorbitol
S. agalactiae	+ (–)	–	–	+	+
S. dysgalactiae	– (+)	–	– (+)	– (+)	–
S. uberis	+	+	+	+	+
S.zooepidemicus	+	­ –	+	–	–

Laboratory Indications of Streptococci

Group A	Group – B	Group – D
Beta – hemolysis	CAMP +	Hydrolysis of bile esculin
Bacitracin sensitive	Beta – hemolysis	Growth in high salt conc