Hemolysis (microbiology)

Hemolysis is used in the empirical identification of microorganisms based on the ability of bacterial colonies grown on agar plates to break down red blood cells in the culture. When the organism has been grown on blood agar plates, it can be classified with regard to whether or not it has caused hemolysis in the red blood cells (RBCs) incorporated in the medium. This is of particular importance in the classification of streptococcal species. A substance that causes hemolysis is a hemolysin.

While a blood agar plate may contain varying concentrations of RBCs and may use blood from a variety of animals, clinical results are most often reported on 5-10% sheep blood agar plates (SBAP).

Types of hemolysis

  • Alpha hemolysis (α-hemolysis) is present if there is a greenish darkening of the agar under the colonies. Streptococcus pneumoniae and Streptococcus viridans display alpha hemolysis. This is sometimes called green hemolysis because of the color change in the agar. Other synonymous terms are incomplete hemolysis and partial hemolysis. Alpha hemolysis is generally caused by peroxides produced by the bacterium.
  • Beta hemolysis (β-hemolysis) is caused by a complete lysis of the red cells in the media. The area around and under the colonies are lightened and transparent. Streptococcus pyogenes, or Group A beta-hemolytic Strep, displays beta hemolysis. Hemolytic tests are also used to differentiate Staphylococcus aureus, which displays beta-hemolysis, from S. epidermidis, a non-hemolytic, commensal species. Beta hemolysis is sometimes called complete hemolysis. Beta hemolysis is caused by hemolysins.
  • Some weakly beta hemolytic species will cause intense beta hemolysis when grown together with a strain of Staphylococcus. This is called the CAMP test1. Streptococcus agalactiae displays this property. Clostridium perfringens can be identified presumptively with this test.
  • If an organism does not cause hemolysis, it is said to display gamma hemolysis (γ-hemolysis): the agar under and around the colony is unchanged (this is also called non-hemolytic). Enterococcus faecalis (formerly called Group D Strep) displays gamma hemolysis.

Notes

1The CAMP test is so called from the initials of those who initially described it, R. Christie, N. E. Atkins, and E. Munch-Peterson.

References

  • Ryan KJ; Ray CG (editors) (2004). Sherris Medical Microbiology, 4th ed., McGraw Hill. ISBN 0-8385-8529-9. 
A central concept in science and the scientific method is that all evidence must be empirical, or empirically based, that is, dependent on evidence or consequences that are observable by the senses. Empirical data is data that is produced by experiment or observation.
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microorganism (also spelled as microrganism) or microbe is an organism that is microscopic (too small to be seen by the human eye). The study of microorganisms is called microbiology.
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agar plate is a sterile Petri dish that contains a growth medium (typically agar plus nutrients) used to culture microorganisms. Selective growth compounds may also be added to the media, such as antibiotics.
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Red blood cells are the most common type of blood cell and the vertebrate body's principal means of delivering oxygen from the lungs or gills to body tissues via the blood.
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Hemolysis. Red blood cells with (right) and without (left and middle) hemolysis.]] Hemolysis (or haemolysis)—from the Latin Hemo-, Greek Αἷμα meaning blood, -lysis
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Red blood cells are the most common type of blood cell and the vertebrate body's principal means of delivering oxygen from the lungs or gills to body tissues via the blood.
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Streptococcus
Rosenbach, 1884

Streptococcus is a genus of spherical Gram-positive bacteria, belonging to the phylum Firmicutes[1] and the lactic acid bacteria group.
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S. pneumoniae

Binomial name
Streptococcus pneumoniae
(Klein 1884)
Chester 1901

Streptococcus pneumoniae, or pneumococcus
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Streptococcus

Streptococcus viridans is a pseudo-taxonomic term for a large group of generally non-pathogenic, commensal streptococcal bacteria that are either α-hemolytic and produce a green (hence the name viridans
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A peroxide is a compound containing an oxygen-oxygen single bond. The simplest stable peroxide is hydrogen peroxide. Superoxides, dioxygenyls, ozones and ozonides compound are considered separately.
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S. pyogenes

Binomial name
Streptococcus pyogenes
Rosenbach 1884

Streptococcus pyogenes is a spherical gram-positive bacteria that grows in long chains [1]
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S. aureus

Binomial name
Staphylococcus aureus
Rosenbach 1884

Staphylococcus aureus /ˌstæf.ə.loˈko.
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S. epidermidis

Binomial name
Staphylococcus epidermidis
(Winslow & Winslow 1908)
Evans 1916

Staphylococcus epidermidis is a member of the bacterial genus Staphylococcus
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Hemolysin is a form of exotoxin protein produced by bacteria which causes lysis of red blood cells in vitro. Visualization of hemolysis of red blood cells in agar plates facilitates the categorization of some pathogenic bacteria such as Streptococcus.
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Staphylococcus
Rosenbach 1884

Species

S. afermentans
S. aureus
S. auricularis
S. capitis
S. caprae
S. cohnii
S. epidermidis
S. felis
S.
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S. agalactiae

Binomial name
Streptococcus agalactiae
Lehmann and Neumann, 1896

Streptococcus agalactiae also known as Group B Streptococcus
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C. perfringens

Binomial name
Clostridium perfringens
Veillon & Zuber 1898
Hauduroy et al. 1937

Clostridium perfringens (formerly known as Clostridium welchii
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E. faecalis

Binomial name
Enterococcus faecalis
(Orla-Jensen 1919)
Schleifer & Kilpper-Bälz 1984

Enterococcus faecalis
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