Medias for bacterial growth
1 / 16

Medias for Bacterial Growth - PowerPoint PPT Presentation

  • Uploaded on

Medias for Bacterial Growth. Objectives. Distinguish between the different types of media used to grow bacteria. Contrast selective and differential medias. Identify bacteria from the growth on agar plates. Growth media-.

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
Download Presentation

PowerPoint Slideshow about ' Medias for Bacterial Growth' - augustus-moser

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript


  • Distinguish between the different types of media used to grow bacteria.

  • Contrast selective and differential medias.

  • Identify bacteria from the growth on agar plates.

Growth media
Growth media-

  • Growth media (singular: medium) are used to cultivate bacteria. Media are mixtures of nutrients that the microbes need to live, and the necessary moisture and pH to support microbial growth

Culture media
Culture Media

  • 1. Chemically Defined

    • the exact chemical composition is known

    • used to grow fastidious organisms

  • 2. Complex Media

    • exact chemical composition is not known

    • most bacteria and fungi are grown with this

Agar is
Agar is…

  • a seaweed extract that becomes a solid at room temperature.

  • Many normal flora and clinically important microbes can be grown either in liquid medium (sometimes called broth), or on Petri dishes when adding agar to the liquid to make it solid.

Selective media
Selective Media

  • Inhibits the growth of some bacteria while selecting for the growth of others

  • Example:

    • Brilliant Green Agar

      • dyes inhibit the growth of Gram (+) bacteria

      • selects for Gram (-) bacteria

      • Most G.I. Tract infections are caused by Gram (-) bacteria

Selective media1
Selective Media

  • EMB (Eosin Methylene Blue)

    • dyes inhibit Gram (+) bacteria

    • selects for Gram (-) bacteria

    • G.I. Tract infections caused by Gram (-) bacteria

Differential media
Differential Media

  • Differentiates between different organisms growing on the same plate

  • When certain microbes grow on that medium, it exhibits a color change that gives us information about the type of microbe growing there.

  • Example:

    • Blood Agar Plates (TSA with 5% sheep blood)

      • used to differentiate different types of Streptococci

Blood agar bap
Blood Agar (BAP)

  • is a differential bacterial growth medium that can distinguish normal from pathogenic bacteria based on the interaction of sheep's blood and bacterial hemolytic enzymes.

  • Alpha hemolysis (α-hemolysis) - bacterial enzymes partially break down the blood cells. Results in a yellowish/greenish/brownish discoloration (like a bruise) around the colony, indicating incomplete hemolysis. – strep throat

  • Gamma hemolysis is no hemolysis at all. The bacteria have no effect on the red blood cells, and no change to the color of the medium. – normal flora/ strep on skin


Bacteria lysis of the RBCs – pathgenic strep

Selective and differential media
Selective and Differential Media

  • Mannitol Salt Agar (MSA)

    • used to identify Staphylococcus aureus

  • Mannitol Salt Agar

    • High salt conc. (7.5%) inhibits most bacteria

    • sugar Mannitol

    • pH Indicator (Turns Yellow when acid)

Nutrient agar
Nutrient Agar

  • TSY (Tryptic Soy Agar)

  • The medium that we use most often in lab is called "TSY" (Tryptic Soy Agar), a complex nutrient medium which supports the growth of a wide variety of microbes.

Selective and differential media1
Selective and Differential Media

  • MacConkey’s Agar

    • used to identify Salmonella

  • MacConkey’s Agar

    • Bile salts and crystal violet (inhibits Gram (+) bacteria)

    • lactose

    • pH Indicator

Many Gram (-) enteric non-pathogenic bacteria can ferment lactose, Salmonella can not

Medias for bacterial growth

  • Bacteria, known as “lactose fermenters”, eat the lactose and in the process create an acidic end product that causes the pH indicator, neutral red, to turn red.  It is the actual colonies of lactose fermenting bacteria that appear pink. Non-lactose fermenting bacteria will be colorless (or, if they have any color, it will be a color other than pink). 

Medias for bacterial growth

  • What Does it Mean if I Find Bacterial Colonies Growing on MacConkey's? 

  • Whenever bacterial colonies are growing on MacConkey’s, you know that they are Gram-negative bacteria (since Gram+ do not grow on this type of medium). If the colonies are pink, you know that they are Gram- lactose fermenting bacteria.