Microbiology Lab Midterm Unit 7 Supportive, Selective, Differential Media (chocolate, TSA, CNA, MacConkey

Supportive media

Additional ingredients that support the growth of more fastidious (picky) bacteria

MacConkey's selective ingredients

Crystal violet and bile salts selective for Gram(-), non-fastidious species, and against everything else

CNA-blood differential ingredients

Defibrinated red blood cells (whole sheep RBC) If the bacteria grow and produce the enzyme hemolysin, they can digest the RBC's in media Level of hemolysis is gamma, alpha, beta

TSA blood agar

Differential media Defibrinated red blood cells Differentiates between a species ability to produce the enzyme hemolysin which breaks down red blood cells. Bacteria that can hemolyze blood utilize the nutrients and iron in the RBCs for growth. Hemolysin production is associated with pathogenicity (Gamma, alpha, beta hemolysis)

Incubation of TSA-blood and CNA-blood

Placed upside down in a candle jar for incubation. The candle jar provides a low oxygen environment that is required for proper function of the bacterial blood hemolysins.

CNA-blood agar

Selective & differential media

MacConkey's

Selective and Differential medium

Chocolate agar

Supportive media medium containing sheep blood cells, the RBCs have been lysed (broken open) to make their contents more readily available to bacteria for growth. Red blood cells are an excellent source of iron, amino acids, and the required bacterial growth factors NAD (factor V) and hemin (factor X).

CNA-blood selective ingredients

colisten and nalidixic acid. Colisten negatively affects the cell membrane of many Gram(-) species, and nalidixic acid inhibits replication of DNA in susceptible species. CNA-blood selects for Gram(+) coccus-shaped species, and against everything else.

beta hemolysis

complete digestion of the blood, the medium under the bacteria is light to clear. Bacteria produce a high level of hemolysins. The bacteria is a likely pathogen.

differential media

differentiate between species that grow on the media according to specific metabolic processes the bacteria may have Has differential ingredient that allows us to determine metabolic processes

MacConkey's differential ingredients

disaccharide lactose and the pH indicator neutral red Bacteria that grow and produce the enzyme lactase are able to ferment the lactose sugar in the medium. This will cause a drop in the pH (to less than 7 , which causes the neutral red to become a bright fuchsia color (non-pathogenic)

gamma hemolysis

no hemolysis. Bacteria grow on top of the medium, but the blood in the medium underneath the cells remains a red color. The bacteria do not produce hemolysins, and are probably not pathogenic.

alpha hemolysis

partial digestion of the blood hemoglobin, the medium has an olive-green color. Bacteria produce some hemolysins. The bacteria is a possible pathogen

Selective media

select for growth of particular bacteria and inhibit (or select against) growth of other types of bacteria