Transcript Lab Differential medium

Differential medium
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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
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Eosin methylene blue
These dyes prevent the growth of G+
Selective for GLactose 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
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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