Selective & Differential Bacterial Growth Media

Specialized bacterial growth media are nutrient-rich substances that are used to grow bacteria in a lab setting. But these media also do more than just grow becateria, Thye also provide information about the bacteria growing there. Specialized media are sometimes selective (only grow certain microbes), sometimes differential (a color change provides additional information about the microbe growing there), or are both selective and differential. Below are links to useful articles and websites about specialized media and their use in the identification of bacteria.

Selective and Differential Media & Bacterial Cultures - SPO Virtual Microbiology Laboratory: When bacterial cultures are grown in a laboratory environment, they are essentially captives, part of a microbial zoo that is dependent on people to provide the proper environment for their survival and growth. A nutrient-rich media is required to grow bacteria in the lab. Some types of growth media go beyond just growing bacteria. They also help identify the micobes growing. This article contains information from an actual college microbiology laboratory exercise on using MacConkey's, Mannitol Salt and Blood agar media.

Differential Bacterial Growth Media - Using Blood Agar, MacConkey’s or Mannitol Salt Medium to ID Bacteria: In microbiology, there are many different techniques used to identify microbes. Differential media typically produce a color change when certain microbes are growing that provides general information regarding identity that help eliminate 'suspects' rather than confirming the specific type of microbe growing.

Selective Bacterial Growth Media - Using MacConkey’s Agar and Mannitol Salt Medium to ID Bacteria: Selective media inhibit the growth of certain microbes. By eliminating 'suspects' the media providing general information regarding the bacteria that are able to grow on this specialized type of agar.

Mannitol Salt Agar (MSA) Bacterial Growth Medium - Differential and Selective Media Used to Identify Staphylococcus Bacteria: Mannitol salt agar has high concentrations of salt that inhibit the growth of most microbes. However Staph bacteria, which is adapted to salty conditions, grows well on MSA. This medium does more than just grw Staph, it produces a color change if pathogenic, disease causing Staph is growing on it.

Blood Agar (BAP) Bacterial Growth Medium - Differential Medium to Identify B-hemolytic Streptococcus: Blood agar (BAP) isnot selective. It is nutrient-rich and will grow many types of microbes. BAP is a differential growth medium which microbiologists use to distinguish clinically significant bacteria from throat and sputum cultures. BAP contains 5% sheep blood. Certain bacteria produce enzymes (hemolysins) that act on the red blood cells to lyse or break them down. The pattern created by the breakdown of blood cells helps provide information on the identity of the bacteria growing on BAP.