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(right) γ-hemolysis (non-hemolytic, S. salivarius) Hemolysis is the breakdown of red blood cells. The ability of bacterial colonies to induce hemolysis when grown on blood agar is used to classify certain microorganisms. This is particularly useful in classifying streptococcal species. A substance that causes hemolysis is called a hemolysin.
A red blood cell in a hypotonic solution, causing water to move into the cell A red blood cell in a hypertonic solution, causing water to move out of the cell. Hemolysis or haemolysis (/ h iː ˈ m ɒ l ɪ s ɪ s /), [1] also known by several other names, is the rupturing of red blood cells (erythrocytes) and the release of their contents into surrounding fluid (e.g. blood plasma).
When alpha-hemolysis (α-hemolysis) is present, the agar under the colony will appear dark and greenish due to the conversion of hemoglobin to green biliverdin. Streptococcus pneumoniae and a group of oral streptococci ( Streptococcus viridans or viridans streptococci) display alpha-hemolysis.
The level of alpha-toxin expressed by a particular strain of S. aureus directly correlates with the virulence of the strain. [2] Recent research has shown that immunization with a mutant form of alpha-toxin that is no longer able to form pores protects against S. aureus pneumonia in mice. Also, introduction of alpha-toxin specific antibodies ...
Enterococci exhibit variable hemolysis on blood agar. Differences occur between species, and between strains of species. More virulent organisms are more likely to exhibit alpha (partial) or beta (complete) hemolysis than less virulent specimens of Enterococcus, which frequently exhibit gamma (absent) hemolysis. [5]
Streptococcus pneumoniae can be differentiated from the viridans streptococci, some of which are also alpha-hemolytic, using an optochin test, as S. pneumoniae is optochin-sensitive. S. pneumoniae can also be distinguished based on its sensitivity to lysis by bile, the so-called "bile solubility test".
Alpha-hemolysin from uropathogenic E. coli produces extra-intestinal infections and can cause cystitis, pyelonephritis, and sepsis. Alpha-hemolysin from Staphylococcus aureus can cause severe diseases, such as pneumonia. Aerolysin from Aeromonas sobria infects the intestinal tract, but it might also cause sepsis and meningitis.
The first group of streptococci is alpha-hemolytic which comprises primarily S.pneumoniae and viridans streptococci. This group is referred to as alpha-hemolysis because the cell membrane of red blood cells is left intact. [2] When cultured, alpha-hemolysis can be deemed present when the agar gel appears greenish. [2]