Presentation on theme: "Differential medium. Differential medium helps us to differentiate one group of bacteria from another. Blood agar – differentiate hemolytic bacteria from."— Presentation transcript:
Differential medium helps us to differentiate one group of bacteria from another. Blood agar – differentiate hemolytic bacteria from nonhemolytic bacteria. 1.RBCs --- beta hemolysin – complete hemolysis When Beta hemolytic bacteria grow on blood agar complete clearing of RBCs round their colonies.
2. alpha hemolysis RBCs ---- alpha hemolysin --- methemoglobin ( green zone around the colonies) partial hemolysis. 3. gamma hemolysis – no hemolysis. No color change in the medium.
Selective medium Allows the growth of some bacteria. This medium prevents the growth of certain other bacteria NaCl agar – facultative halophiles such as S. aureus will grow while other bacteria such as E. coli cannot grow Looking for growth - colonies
EMB Eosin methylene blue These dyes prevent the growth of G+ Selective for G- Lactose makes the medium differential Fermenters make pink colonies Nonfermenters make colorless or white colonies Both selective and differential E. coli makes shiny green ( metallic green sheen colonies) – lactose fermenter.
McConkey agar Crystal violet, bile salts prevent the growth of G+. Selective for G- Differential medium Lactose Fermenters make pink colonies Nonfermenters make colorless or white colonies.
Triple Sugar iron agar TSI medium Three sugars 0.1% glucose 1% lactose 1% sucrose Peptone Iron Phenol red
Entire medium yellow – fermeneted one or both of the disaccharides in addition to glucose. Entire medium is red – none of the sugars were fermented. Red slant and rest of the medium yellow – only glucose fermented – S. flexneri Red slant and most of the medium black Most likely bacteria fermented only glucose and also produced hydrogen sulfide