Plates Quiz Flashcards
Composition of manitol salt agar
Carbohydrate mannitol
Sodium chloride
Phenol red indicator
What are the colors phenol red turns at which pH
It is yellow below. pH. 6.8
Red at pH. 7.4 to 8.4
Pink at pH. 8.4 and above
What does the mannitol do in manitol salt? Agar
Provides the substrate for fermentation and makes the medium differential
What does the sodium chloride do in the manitol salt agar
Makes the medium selective because its concentration is high enough to dehydrate and kill most bacteria
What type of bacteria typically thrives on manitol salt agar and why?
Staph aureus because of their adaptation to salty habitats such as human skin
How does staph Aureus react to manitol?
It ferments the mannitol which produces acids and lowers the pH of the medium
What is manitol salt agar used for
Isolation differentiation of staphylococcus aureus
With the manitol salt agar, what are the results with
Poor growth
Good growth
Yellow growth or Halo?
Red growth no. Halo
Poor growth. The organism is inhibited by the NaCl so it is not staphylococcus
Good growth. The organism is not inhibited by NaCl so it is definitely staphylococcus
Yellow, growth or Halo. The organism produces acid for mannitol fermentation possible pathogenic staphylococcus aureus
Red growth or no Halo. The organism does not ferment mannitol so it is a staphylococcus other than s. Aureus
What are the characteristics of eosine methylene blue or EMB agar?
It is a complex (chemically undefined) selective and differential medium
It contains the dyes eosin y and methylene blue
What are the purpose of the dyes in EMB agar
They inhibit the growth of most gram-positive organisms
They react with vigorous lactose fermenters whose acid end-products turn the growth dark, purple or black
What are the results of using methylene blue agar for
Poor growth or no growth
Good growth
Growth is pink and mucoid
Growth is dark( purple to Black with or without green metallic Sheen)
Growth is colorless meaning not purple, green, red or pink
Poor growth means organism is inhibited by eosin and or methylene blue equals gram-positive bacteria
Good growth organism is not inhibited by eosin and methylene blue equals gram-negative bacteria
Growth is pink and mucoid. Organism ferments lactose with little acid production equals possible coliform bacteria
Growth is dark purple to Black with or without green. Metallic Sheen means organism ferments lactose with acid production equals probable coliform
Growth is colorless means organism does not ferment lactose equals non-coliform bacteria
What are the characteristics of macconkey agar
It is a selective and differential medium containing lactose bile salts neutral red and Crystal Violet
What is the purpose of bile salts and Crystal Violet in McConkey agar?
Bile salts and Crystal Violet inhibit growth of gram-positive bacteria
What is the purpose of the neutral red dye in McConkey agar?
It is a pH indicator that is colorless above a pH of 6.8 and red pH less than 6.8
In McConkey agar what are the results of
Poor growth or no growth
Good growth
Pink to Red growth with or without bile precipitate
Growth is colorless meaning not red or pink
Poor growth indicates organism is inhibited by Crystal Violet and or bile equals gram-positive bacteria
Good growth indicates organism is not inhibited by Crystal Violet or bile equals gram-negative bacteria
Pink to red growth with or without bile precipitate indicates organism produces acid from lactose fermentation equals probable coliform
Growth is colorless indicates organism does not ferment lactose equals non-coliform bacteria
What is the purpose of the lactose in the McConkey agar?
It selects for organisms that ferment lactose to acid high end-products that lower the pH
What are the characteristics of the hektoen enteric agar
It is a complex (chemically undefined) moderately selective and differential medium designed to isolate salmonella and shingella species
What is the HE test based on
The ability to ferment lactose sucrose or salicin to acid end products and to reduce sulfur to hydrogen sulfide gas
What is the purpose of the ferric ammonium citrate in the he test
It is included as a source of oxidized iron to react within a H2S produced to form the black precipitate ferrous sulfide
What are the purpose of bile salts in the he test and what is included to help their inhibitory effects?
They are included to prevent or inhibit the growth of gram-positive organisms
A relatively high concentration of animal tissue and yeast extract are included to offset their inhibitory effects
What is included to indicate pH changes in the he agar
Bromothymal blue and acid fusion dyes
What is interpretation of the he test results including
Poor growth or no growth
Good growth
Pink to orange growth
Blue green growth with black precipitate
Blue green growth without black precipitate
Poor growth means organism is inhibited by bile and or one of the dyes included equals gram-positive bacteria
Good growth means organism is not inhibited by bile or any of the dyes included equals gram-negative bacteria
Pink to Orange growth means organism produces acid from lactose sucrose and or salicin fermentation equals not shingella or salmonella
Blue or green growth with black precipitate means organism does not ferment lactose sucrose or salicin but reduces sulfur to hydrogen sulfide equals probable salmonella bacteria
Blue or green growth without black precipitation means organism does not ferment lactose sucrose or salicin or reduce sulfur equals probable shingella or rarely salmonella bacteria
