Term
salts
MSA (mannitol salt agar) is selective for halophile bacteria. |
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Definition
What inhibits some bacteria from growing in MSA Agar?
dyes
alcohol
mannitol
salts |
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Term
methylene blue
EMB contains methylene blue (the "MB" part of the name) which is toxic to Gram + bacteria. Therefore, EMB grows up Gram - only which are not affected by the methylene blue. |
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Definition
What inhibits G+ from growing In EMB?
methylene blue
alcohol
bile salts
antibiotics |
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Term
bile salts
MacConkey contains bile salts which are similar to the bile salts that come out of our gallbladder that digest fats we eat. Bile salts are detrimental to Gram + bacteria, therefore MAC will kill off any G+ bacteria that is streaked onto the MAC plate. This also accounts for the fact that most of our intestinal bacteria are Gram - because they can make it past the bile salts, but Gram + cannot. |
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Definition
What inhibits G+ from growing in MacConkey?
methylene blue
alcohol
bile salts
antibiotics |
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Term
Bacteria that are found in the intestine.
Coliform refers to bacteria which can be found living in the intestinal tract. Think of the word "colon". This was also the term used when naming "E. coli". You may see a notice that a beach is closed due to high coliform counts. This usually means that the water was tested and too much E. coli was found which could indicate contamination of the water by sewage - something you don't want to swim in! Although E. coli itself usually will not harm you, this bacteria is used as a "measuring stick" for other possible pathogenic coliform bacteria which may be lurking in sewage along with the E. coli. |
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Definition
What does the term “coliform” mean?
Bacteria which are lactose fermenters
Bacteria that are found in the intestine.
To be able to produce colored colonies.
To be able to grow on special media. |
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Term
selective for Gram - bacteria and differential for lactose fermenters
MacConkey is selective for Gram - bacteria only. It is also differential for lactose fermenters. If a Gram - is grown on MAC, if it is a lactose fermenter, it will produce colorful colonies, usually pink, although some can have purple mixed in too. If the G- bacteria does not have the ability to ferment lactose, it will grow on MAC, but it will not produce colorful colonies, but grow its usual colors like tan or gray. |
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Definition
What is MacConkey selective for and is it also differential?
selective for Gram + bacteria but it is not a differential agar
selective for Gram - bacteria and differential for lactose fermenters
selective for Gram + bacteria and differential for lactose fermenters
selective for Gram - bacteria, but it is not a differential agar |
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Term
selective for Gram - bacteria and differential for lactose fermenters
EMB is selective for Gram - bacteria only. It is also a differential agar for lactose fermenters which will grow very colorful colonies. Lactose fermenters produce colonies with colors ranging from pink to purple to metallic green (E. coli turns green). Gram - bacteria which cannot ferment lactose will grow on EMB, but they will retain their normal colony color (usually tan or gray). |
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Definition
What is EMB agar selective for and is it also differential agar?
selective for Gram + bacteria and differential for lactose fermenters
selective for Gram + bacteria but it is not a differential agar
selective for Gram - bacteria and differential for lactose fermenters
selective for Gram - bacteria, but it is not a differential agar |
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Term
selective for Gram + bacteria, but it is not a differential agar
PEA (Phenylethyl Alcohol Agar) is selective for Gram + bacteria only. It is not a differential agar though. The only information you can gather about a bacteria that grows on PEA is that it is G+. |
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Definition
What is PEA agar selective and differential for?
selective for Gram - bacteria and differential for lactose fermenters
selective for Gram + bacteria, but it is not a differential agar
selective for Gram + bacteria, and differential for lactose fermenters
selective for Gram - bacteria, but it is not a differential agar |
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Term
growth with tan or colorless colonies
This bacteria is a Gram -, therefore it will grow on EMB which is selective for G- bacteria. However, the colonies will not change from their normal tan/colorless colonies because it is not fermenting lactose. EMB is a differential agar which will cause lactose fermenting bacteria to pick up colors as they form colonies. |
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Definition
What results would you obtain if you streaked out a non-lactose fermenting G- onto EMB?
growth with tan or colorless colonies
no growth
growth with pink colonies
growth with metallic green colonies |
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Term
growth with tan colorless colonies
E. coli is a Gram - bacteria, therefore it would grow on MacConkey agar which is selective for Gram - bacteria. However, because it is a "non-lactose fermenting" strain of E. coli, you should not see any of the differential colors which indicate fermentation of this sugar. |
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Definition
What results would you obtain if you streaked out a non-lactose fermenting G- onto MacConkey?
no growth
growth with pink colonies
growth with metallic green colonies
growth with tan colorless colonies |
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Term
no growth
Staphylococcus aureus is a Gram + bacteria. Therefore, it would not grow on EMB which is selective for G- bacteria only. |
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Definition
What results would you obtain if you streaked out Staphylococcus aureus on EMB?
no growth
growth with metallic green colonies
growth with pink colonies
growth with tan colonies |
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