Question

Confirmed test Streak a sample from the positive lactose broth tubes on to eosin-methylene blue agar plates. This medium is both selective and differential. Eosin Methylene Blue (EMB): selective, differential Peptone 10 g Lactose 5 g Sucrose 5 g K2HPO4 2 g Agar 13.5 g Eosin Y 0.5 g MB 0.06 g The dyes can readily enter into gram positive cells by diffusing through the peptidoglycan layer to the cell membrane. The outer membrane of gram negative organisms prevents access through the cell wall making this a selective medium for gram negative bacteria. EMB is also a differential medium. The medium also contains lactose and those organisms that can ferment lactose will reduce the pH resulting in colonies that with a blue-black appearance often with a green sheen (E. coli below left). Non-lactose fermenters grow as colorless or translucent colonies (Proteus vulgaris, below right). 16.6 : Explain why Proteus or Enterrobacter are not considered coliforms.

          Confirmed test
Streak a sample from the positive lactose broth tubes on to eosin-methylene blue agar plates. This
medium is both selective and differential.
Eosin Methylene Blue
(EMB):
selective, differential
Peptone 10 g
Lactose 5 g
Sucrose 5 g
K2HPO4 2 g
Agar 13.5 g
Eosin Y 0.5 g
MB 0.06 g
The dyes can readily enter into gram positive cells by diffusing through the peptidoglycan layer to
the cell membrane. The outer membrane of gram negative organisms prevents access through the
cell wall making this a selective medium for gram negative bacteria.
EMB is also a differential medium. The medium also contains lactose and those organisms that can
ferment lactose will reduce the pH resulting in colonies that with a blue-black appearance often with
a green sheen (E. coli below left). Non-lactose fermenters grow as colorless or translucent colonies
(Proteus vulgaris, below right).
16.6 : Explain why Proteus or Enterrobacter are not considered coliforms.

Confirmed test
Streak a sample from the positive lactose broth tubes on to eosin-methylene blue agar plates. This
medium is both selective and differential.
Eosin Methylene Blue
(EMB):
selective, differential
Peptone 10 g
Lactose 5 g
Sucrose 5 g
K2HPO4 2 g
Agar 13.5 g
Eosin Y 0.5 g
MB 0.06 g
The dyes can readily enter into gram positive cells by diffusing through the peptidoglycan layer to
the cell membrane. The outer membrane of gram negative organisms prevents access through the
cell wall making this a selective medium for gram negative bacteria.
EMB is also a differential medium. The medium also contains lactose and those organisms that can
ferment lactose will reduce the pH resulting in colonies that with a blue-black appearance often with
a green sheen (E. coli below left). Non-lactose fermenters grow as colorless or translucent colonies
(Proteus vulgaris, below right).
16.6 : Explain why Proteus or Enterrobacter are not considered coliforms.

Added by David D.

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