GCU B io 205 Lab Final
Exam Qu estions and
answ er s w ith accu r ate
r ationales(PASSED)
Selective medium- give examples - answer Allows the growth of certain bacteria
while preventing or retarding the growth of other bacteria.
Ex: mannitol salt agar, eosin methylene blue (EMB) agar, HEA agar
Differential medium- give examples - answer Allows for growth of all bacteria
while differentiating them from one another.
Ex: MacConkey Agar, blood agar
MacConkey agar selects for which group of bacteria? explain - answer Gram
negative because the crystal violet inhibits the growth of gram positive.
MacConkey agar media differentiates between enteric bacteria based on what
biochemical reaction? Explain - answer Lactose fermentation which is the mixture
of carb lactose, bile salts, and pH indicator neutral red which permits
differentiation of enteric bacteria.
, If the organism is E. coli, what would you see on your plate? explain. - answer You
would see pink it is a coliform bacteria which is a lactose fermenter that produces
lactic acid by fermenting the lactose in the media
If the organism(s) is/are other enteric, what would you see on your plate? explain.
- answer Coliform bacteria- pink/red colonies because the pH is lowered and they
are lactose fermenters
Dysentery, typhoid, and paratyphoid would indicate beige and transparent
colonies because they are lactose non-fermenters
EMB agar selects for which group of bacteria? explain - answer Gram negative
bacteria.
The dyes eosin Y and methylene blue inhibit the growth of gram positive bacteria
and allow the gram negative to grow.
EMB agar media differentiates between gram negative enteric based on what
biochemical reaction? - answer Lactose fermentation. Large amounts of acid are
produced, metallic green. small amounts will make the colonies pink/red. No
fermentation= colorless colonies
If the organism is E.coli, what would you see on your plates? - answer Green
metallic because the bacteria is gram negative and because of lactic acid.
If the organism is/are other enterics, what would you see on your plate? explain. -
answer Purple/pink colonies from no lactose fermentation
Exam Qu estions and
answ er s w ith accu r ate
r ationales(PASSED)
Selective medium- give examples - answer Allows the growth of certain bacteria
while preventing or retarding the growth of other bacteria.
Ex: mannitol salt agar, eosin methylene blue (EMB) agar, HEA agar
Differential medium- give examples - answer Allows for growth of all bacteria
while differentiating them from one another.
Ex: MacConkey Agar, blood agar
MacConkey agar selects for which group of bacteria? explain - answer Gram
negative because the crystal violet inhibits the growth of gram positive.
MacConkey agar media differentiates between enteric bacteria based on what
biochemical reaction? Explain - answer Lactose fermentation which is the mixture
of carb lactose, bile salts, and pH indicator neutral red which permits
differentiation of enteric bacteria.
, If the organism is E. coli, what would you see on your plate? explain. - answer You
would see pink it is a coliform bacteria which is a lactose fermenter that produces
lactic acid by fermenting the lactose in the media
If the organism(s) is/are other enteric, what would you see on your plate? explain.
- answer Coliform bacteria- pink/red colonies because the pH is lowered and they
are lactose fermenters
Dysentery, typhoid, and paratyphoid would indicate beige and transparent
colonies because they are lactose non-fermenters
EMB agar selects for which group of bacteria? explain - answer Gram negative
bacteria.
The dyes eosin Y and methylene blue inhibit the growth of gram positive bacteria
and allow the gram negative to grow.
EMB agar media differentiates between gram negative enteric based on what
biochemical reaction? - answer Lactose fermentation. Large amounts of acid are
produced, metallic green. small amounts will make the colonies pink/red. No
fermentation= colorless colonies
If the organism is E.coli, what would you see on your plates? - answer Green
metallic because the bacteria is gram negative and because of lactic acid.
If the organism is/are other enterics, what would you see on your plate? explain. -
answer Purple/pink colonies from no lactose fermentation
