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The plates are incubated for 12 hours up to several days, depending on the test that is performed. Commonly used types of agar plates include: Red blood cells on an agar plate are used to diagnose infection. On the left is a positive Staphylococcus infection, on the right a positive Streptococcus culture.
Streptolysin O is an oxygen-sensitive cytotoxin secreted by most Group A streptococcus (GAS) and Streptococcus dysgalactiae; it interacts with cholesterol in the membrane of eukaryotic cells (mainly red and white blood cells, macrophages, and platelets), usually resulting in β-hemolysis under the surface of blood agar. Streptolysin S is an ...
When certain microorganisms are grown on blood agar, they may digest the blood in the medium, causing visible hemolysis (destruction of red blood cells) on the agar plate. In colonial morphology, hemolysis is classified into three types: alpha-, beta-, and gamma-hemolysis.
Streak a beta-lysin–producing strain of aureus down the center of a sheep blood agar plate. The test organism streak should be 3 to 4 cm long. Streak test organisms across the plate perpendicular to the S. aureus streak within 2 mm. (Multiple organisms can be tested on a single plate). Incubate at 35°-37°C in ambient air for 18-24 hours.
This type of test is considered a diffusion test. [18] In agar and broth dilution methods, bacteria are placed in multiple small tubes with different concentrations of antibiotics. [14] Whether a bacterium is sensitive or not is determined by visual inspection or automatic optical methods, after a period of incubation. [5]
Chocolate agar (CHOC) or chocolate blood agar (CBA) is a nonselective, enriched growth medium used for isolation of pathogenic bacteria. [ 1 ] [ 2 ] [ 3 ] It is a variant of the blood agar plate , containing red blood cells that have been lysed by slowly heating to 80°C.
A blood culture is a medical laboratory test used to detect bacteria or fungi in a person's blood. Under normal conditions, the blood does not contain microorganisms : their presence can indicate a bloodstream infection such as bacteremia or fungemia , which in severe cases may result in sepsis .
The main criterion for differentiation between Staphylococcus spp. and Streptococcus spp. is the catalase test. Staphylococci are catalase positive whereas streptococci are catalase-negative. [2] S. pyogenes can be cultured on fresh blood agar plates.