©JUSTTRACY EXAM SOLUTIONS
21/11/202410:20AM
Microbiology LAB UTC - Barbosa Exam
Questions And Improved Responses
What does MSA stand for? - answers✔✔Mannitol Salt Agar
What does MAC stand for? - answers✔✔MacConkey's Agar
What does EMB stand for? - answers✔✔Eosin Methylene Blue Agar
How is the MSA test selective, and what type of bacteria growth does it NOT inhibit (allows
to grow)? - answers✔✔It contains mannitol (sugar) which is used for fermentation
The high salt concentration inhibits the growth of most bacteria other than staphylococci
How is the MSA test differential? - answers✔✔the phenol red is a pH indicator that changes
from red to yellow when the bacteria ferments the mannitol and produces an acid
On the MSA test, which bacteria shows growth AND produces a color change? -
answers✔✔Staphylococcus aureus
On the MSA test, which bacteria produces colonies but does NOT produce a color change? -
answers✔✔Staphylococcus epidermis
How is the MAC test selective, and which type of bacteria does it inhibit growth? -
answers✔✔The crystal violet and bile salts inhibit the growth of gram-Positive organisms
The lactose in the agar allows for fermentation
How is the MAC test differential? - answers✔✔The lactose allows for fermentation, whose
acid end-products act on bile salts, and neutral red is absorbed by the precipitated salts.
, ©JUSTTRACY EXAM SOLUTIONS
21/11/202410:20AM
Non-fermenting bacteria give an alkaline reaction and are non colored/transparent.
On the MAC test, which bacteria produced red/pink colonies? - answers✔✔Escherichia coli
On the MAC test, which bacteria produced colorless colonies? - answers✔✔Salmonella
enteritidis
How is the EMB test selective? - answers✔✔The methylene blue acts as an inhibitor to gram-
Positive organisms.
Both lactose and saccharose are included to allow for fermentation.
How is the EMB test differential? - answers✔✔INDICATOR for those that ferment lactose
and those that do not... eosin & methylene blue
Strong lactose fermentation = green metallic sheen
Weak lactose fermentation/ prefer saccharose = pinkish colonies, mucoid, larger colonies
No fermentation = colorless
On the EMB test, which bacteria produced a green metallic sheen? - answers✔✔Escherichia
coli
On the EMB test, which bacteria produced pinkish colonies? - answers✔✔Enterobacter
aerogenes
On the EMB test, which bacteria were colorless? - answers✔✔Salmonella enteritidis
21/11/202410:20AM
Microbiology LAB UTC - Barbosa Exam
Questions And Improved Responses
What does MSA stand for? - answers✔✔Mannitol Salt Agar
What does MAC stand for? - answers✔✔MacConkey's Agar
What does EMB stand for? - answers✔✔Eosin Methylene Blue Agar
How is the MSA test selective, and what type of bacteria growth does it NOT inhibit (allows
to grow)? - answers✔✔It contains mannitol (sugar) which is used for fermentation
The high salt concentration inhibits the growth of most bacteria other than staphylococci
How is the MSA test differential? - answers✔✔the phenol red is a pH indicator that changes
from red to yellow when the bacteria ferments the mannitol and produces an acid
On the MSA test, which bacteria shows growth AND produces a color change? -
answers✔✔Staphylococcus aureus
On the MSA test, which bacteria produces colonies but does NOT produce a color change? -
answers✔✔Staphylococcus epidermis
How is the MAC test selective, and which type of bacteria does it inhibit growth? -
answers✔✔The crystal violet and bile salts inhibit the growth of gram-Positive organisms
The lactose in the agar allows for fermentation
How is the MAC test differential? - answers✔✔The lactose allows for fermentation, whose
acid end-products act on bile salts, and neutral red is absorbed by the precipitated salts.
, ©JUSTTRACY EXAM SOLUTIONS
21/11/202410:20AM
Non-fermenting bacteria give an alkaline reaction and are non colored/transparent.
On the MAC test, which bacteria produced red/pink colonies? - answers✔✔Escherichia coli
On the MAC test, which bacteria produced colorless colonies? - answers✔✔Salmonella
enteritidis
How is the EMB test selective? - answers✔✔The methylene blue acts as an inhibitor to gram-
Positive organisms.
Both lactose and saccharose are included to allow for fermentation.
How is the EMB test differential? - answers✔✔INDICATOR for those that ferment lactose
and those that do not... eosin & methylene blue
Strong lactose fermentation = green metallic sheen
Weak lactose fermentation/ prefer saccharose = pinkish colonies, mucoid, larger colonies
No fermentation = colorless
On the EMB test, which bacteria produced a green metallic sheen? - answers✔✔Escherichia
coli
On the EMB test, which bacteria produced pinkish colonies? - answers✔✔Enterobacter
aerogenes
On the EMB test, which bacteria were colorless? - answers✔✔Salmonella enteritidis
