Some bacteria has the ability to lyse erythrocytes from the culture
substrate. This property can be examined both on liquid and solid
blood-containing media. Most used is the sheep blood agar, composed of
tryptic soy agar supplemented with 5 to 10% blood.
Multiplying bacteria on blood agar may have the following results:
1. bacterial growth with no medium changes = non-hemolytic bacteria
(also known as gamma hemolysis) .
2. a clear area sorrounding the colonies caused by the complete lysis of
the erythrocytes = beta hemolysis
3. a greenish area around colonies caused by the incomplete lysis of the
erythrocytes = alpha hemolysis (hemoglobin is transformed in
methemoglobin under H2O2 produced by bacteria - viridans effect).
A type of hemolysis do not exclude the other; members of the
Staphylococcus genus frequently produce double hemolysis: alpha and
beta. Alpha hemolysis becomes more visible after placing the blood agar
at 4 °C for few hours.
1. H. Raducanescu, V.Bica-Popii,1986. Bacteriologie veterinara, Ed. Ceres, Bucuresti.
2. Margaret Barnett, 1992. Microbiology Laboratory Exercises. Wm. C. Brown Publishers.
3. Murray, P.R., Baron, E. J., Jorgensen, J.J., Pfaller, M.A., and Yolken, R.H. Manual of Clinical Microbiology, 8th ed.
ASM Press: Washington, DC, 2003.
|Escherichia coli beta haemolysis
on sheep blood agar
alpha & beta haemolysis
Rabbit, horse, bovine or human blood may also be used for different
types of blood media.
A demonstration of blood harvesting from a ram is available in video
See also "Blood agar preparation" video.
(c) Costin Stoica