Some bacteria have 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
|Pseudomonas aeruginosa haemolysis on sheep
Multiplying bacteria on blood agar may have the following results:
1. bacterial growth with no medium changes = non-haemolytic bacteria (also known
as gamma haemolysis) .
2. a clear area surrounding the colonies caused by the complete lysis of the
erythrocytes = beta haemolysis
3. a greenish area around colonies caused by the incomplete lysis of the erythrocytes
= alpha haemolysis (hemoglobin is transformed in methemoglobin under H2O2
produced by bacteria - viridans effect).
A type of haemolysis do not exclude the other; members of the Staphylococcus genus
frequently produce double haemolysis: alpha and beta. Alpha-haemolysis becomes
more visible after placing the blood agar at 4 °C for few hours.
1. Helgomar Raducanescu, Valeria Bica-Popii,1986. Bacteriologie veterinara, Ed.
2. Margaret Barnett, 1992. Microbiology Laboratory Exercises. Wm. C. Brown
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
(c) Costin Stoica