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22.4: Blood Agar Plates (BAP)

  • Page ID
    40298
  • Introduction

    Blood Agar is an important clinical medium. It is both enriched and differential. The blood contains many nutrients that help support “fastidious” bacteria, those that need additional or particular types of nutritional support. Many bacteria can hemolyze blood, partially or completely, and these hemolysis patterns can help differentiate and identify certain bacterial pathogens. The blood agar we use in lab is commercially prepared and has a TSA base with 5% Sheep’s blood added to it. To prepare the medium, the TSA is cooled, the blood is added aseptically, and then the plates are poured. (1)

    There are two types of hemolysis. Alpha-hemolysis (α) is caused by damage (but not lysis) of the RBCs in the blood; the media is translucent with a green-ish tinge around the colonies (1). Beta-hemolysis (β) is lysis of the RBCs and the media looks completely transparent around the colonies.

    Non-hemolytic (often called gamma-hemolysis, γ) bacteria exhibit neither lysis nor clearing of any kind.

    (Not available during the unknowns)

    clipboard_e1073b5290af70225cabdec0b4ee0700e.png
    Figure \(\PageIndex{1}\): HemolysisStreptococcus . Spp (Left) alpha-Hemolysis ( S.Mitis ); (Middle) beta-Hemolysis ( S. Pyogenes );

    (Right) gamma-Hemolysis (= Non-Hemolytic, S. Salivarius ) GFDL and CC-by-SA 2.5, 2.0, 1.0

    https://ja.Wikipedia.org/wiki/%E8%A1%80%E6%B6%B2%E5%AF%92%E5%A4%A9%E5%9F%B9%E5%9C%B0

    clipboard_ec3e8a76e11ef1ba4980828ea5d2d2fc5.png
    Figure \(\PageIndex{2}\): BAP exhibiting hemolysis patterns, particularly beta-hemolysis in the upper right. K.C. Burke CC BY-NC SA

    Materials

    • Gloves
    • 1 Blood Agar Plate (BAP)/group
    • Lactococcus lactis
    • Staphylococcus aureus (One slant per table is provided at the front table)
    • Staphylococcus epidermidis

    Procedures

    1. Label the plates, and “split” into 3 quadrants, labeling each quadrant with the name of one of the 3 organisms.
    2. Inoculate the 3 organisms onto a BAP and stab the inoculation with the loop along the streak line.

    Alpha (α) Hemolysis (Lactococcus lactis)

    Beta (β) Hemolysis (Staphylococcus aureus)

    Gamma (γ) Hemolysis (Staphylococcus epidermidis)

    Safety

    Staphylococcus aureus is a BSL2 organism. Wear glove while handling.

    Results

    Record your observations.

    Bacterium

    Hemolysis pattern

    Description

    Conclusion

    • In your own words, explain the mechanism behind Blood Agar (how it works), and why you think it is a good growth medium for fastidious bacteria.

    Resources

    1. Rebecca Buxton. 2005. Blood agar plates and hemolysis protocols. Web. 1 October 2016 http://www.asmscience.org/content/education/protocol/protocol.2885

    Contributors and Attributions