What blood tests are done in bacterial infections?īlood tests require a sample of blood accessed by a needle from a vein. The catalase test differentiates catalase-positive staphylococci and micrococci from catalase-negative streptococci. The production of bubbles (oxygen) indicates a positive result. The bacterial sample is added to a test tube of hydrogen peroxide. Catalase testĬatalase is an enzyme that degrades hydrogen peroxide into hydrogen and oxygen. The coagulase test differentiates coagulase-positive Staphylococcus aureus from coagulase-negative staphylococci. ![]() *Note palisading/ paralleling of cells in 'Chinese lettering' formation What other tests can be done with bacterial cultures? Coagulase testĬoagulase is an enzyme produced by certain bacteria that converts fibrinogen to fibrin and is observed as clumping of cells in plasma. Gram-positive bacilli: corynebacteria cultured from forearm skin* Some bacteria form clusters whilst others form chains.The Gram stain also identifies the bacterium's shape and behaviour. A Gram-negative bacterium appears red, as it is counterstained with a red dye such as saffron.A Gram-positive bacterium appears purple due to crystal violet dye adhering to the cell wall.A Gram stain can be done on the original sample, but it is usually done on cultured bacteria after transferring a colony of bacteria from the agar plate to a glass microscope slide. To identify bacterial antibiotic resistance patterns.Ī Gram stain uses a series of stains or dyes on a sample, followed by inspection under a light microscope to detect and identify bacteria as Gram-positive or Gram-negative.Whether the bacteria are resistant to selected antibiotics.The effectiveness of particular antibiotics against particular bacteria.Antibiotic susceptibility testing is used to determine: ![]() This information allows the selection of the most suitable antibiotic to treat a particular infection. ![]() Antibiotic sensitivity testing determines which antibiotics inhibit the growth of the bacteria that have been cultured.
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