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42 Cards in this Set
- Front
- Back
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When we are looking to see whether a bacteria ferments lactose, what are we really determining?
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What metabolism enzymes are present
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Escherichia coli and proteus miribilis:
Are both usually acquired in hospital settings – Are both gram-positive – are common causes of UTI |
Are common causes of UTI
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You are working for the CDC after hurricane and are testing to find out if the water supplies have been contaminated by sewage. What will you be looking for on EMB plates? (choose all that apply)
–nothing growing at all – Purple colonies from lactose fermenting E. coli –purple colonies from Enterobacter aerogenes - metallic green colonies from lactose fermenting E. coli - yellow colonies from salt tolerance staphylococci |
– Purple colonies from Enterobacter aerogenes
- metallic green colonies from lactose fermenting E. coli |
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What do you think the buffers in the recipe like EMB are important? (Hint: buffers control the starting pH).
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The starting pH must be the right for the color change to occur with fermentation
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Match the ingredients to what they supply.
– Peptone – Lactose – Sucrose – Carbon and nitrogen – Carbon from milk sugar – Carbon |
Peptone = carbon and nitrogen
Lactose = carbon from milk sugar Sucrose = carbon |
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Match the ingredients to their function:
–Bromthymol blue – sucrose – Lactose – Ferric ammonium sulfate – PH indicator – Carbon source – Carbon source from milk sugar – Sulfur indicator |
Bromthymol blue = PH indicator Sucrose = carbon source Lactose = carbon source from milk sugar Ferric ammonium sulfate = Sulfur indicator |
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You have various dishes served at a company picnic for numerous people developed food poisoning. You test the dishes on Hektoen Enteric plates. Match the results with the type of food poisoning.
– Egg salad turns black on HE –Hamburgers turn yellow on HE –Potato salad turns green on HE –salmonella – E. coli – Shigella |
Egg salad turns black on HE = Salmonella
Hamburgers turn yellow on HE = E. coli Potato salad turns green on HE = Shigella |
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You have made a batch of HE media and accidentally left out the ferric ammonium citrate. What will happen?
– Both salmonella and E. coli will appear yellow – Both shigella and E. coli will appear yellow – Both salmonella and Shigella will appear green – Both Shigella and E. coli will appear green – Nothing will appear yellow |
– Both salmonella and Shigella will appear green |
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Some strains of E. coli are able to ferment lactose, and some are not. You street a sample of broth onto MAC, knowing its E. coli. The colonies turns slightly yellow. What does that mean?(Choose all that apply)
– You have contamination – Your E. coli is able to ferment lactose – Your E. coli is unable to ferment lactose – Your E. coli contains lactase enzyme – Your E. coli does not contain lactase |
– Your E. coli is unable to ferment lactose
– Your E. coli does not contain lactase |
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Your patient has food poisoning, and the samples turn metallic green on EMB, yellow on HE, and pink on MAC. What do you decide is the culprit?
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E. coli
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Your patient has food poisoning, and the samples turn dark purple on EMB, dont grow on HE, and pink on MAC. What do you decide is the culprit?
– Enterobacter aerogenes – Salmonella – Shigella – E. coli |
Enterobacter aerogenes |
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A common cause of hospital acquired infections and skin infections |
Pseudomonas aeruginosa
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A common cause of foodborne G.I. infection
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Salmonella and Shigella species
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Part of the natural flora of the gut, and important for health (this bacteria makes some of our bodies vitamins). But some types can contain toxins that cause disease. It is an ________ bacteria that often strongly ferments what two things?. Salmonella, on the other hand, cannot ferment lactose, they can reduce ______.
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E. Coli; enteric; E. coli = lactose, glucose. Salmonella = no lactose, sulfur. |
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Eosin methylene blue agar selects for?
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Gram Negatives |
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Eosin methylene blue agar contains the dyes ______ and ______. |
Eosin Y, Methylene blue |
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The dyes in the Eiosin methylene blue agar, Eosin Y and methylene blue inhibit the growth of _______ organisms. In addition, the dyes function as an ______, Producing a dark ____ color under slightly acidic conditions, and a dark _____ color under more acidic conditions. Under very acidic conditions, the dye will produce a ___________ on bacterial colony
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Gram positive; indicator; slightly acidic = pink; more acidic = purple; very acidic = Green metallic sheen
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In which two tests does acid cause color change as a result of the fermentation of sugars?
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EMB and MSA |
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EMB contains what three things as carbon sources, and what kind of growth does this encourage? |
Lactose, sucrose, peptone; fecal coliforms
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Bacteria most commonly found in the human colon and store samples
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Fecal coliforms |
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In EMB tests, why are the gradiations of color change useful? |
Because strains of E. coli that are capable of fermenting lactose produce a lot of acid (and usually have a metallic green hue); Enterobacter aerogenes usually from it lactose slowly and take on a pink to purple color.
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Your unknown sample results show a metallic green hue on your EMB. What does this indicate and why?
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Presence of E. coli, high acidity; E. coli can ferment lactose, which produces a great amount of acid
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You're unknown sample results show a pink to purple color on your EMB. What does this indicate and why?
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Possible presence of Enterobacter Aerogenes, slight/medium acidity; can ferment lactose, but does it slowly, producing a slight/medium amount of acid
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Why are the gradations of color useful in an EMB test?
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Because of this creation characteristic, and mixed sample streaked on EMB can result in isolated colonies with different colors, which can then be streaked themselves onto plates, allowing for the isolation of multiple strains from a single sample
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Hektoen Enteric Agar contains ________, which inhibit most gram __________ bacteria. The agar contains ingredients that allow for the isolation of _____ and _____ from other enteric bacteria.
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Bile salts; Positive; Salmonella, Shigella |
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Which two types of tests select for Graham negative?
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EMB and HE |
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Hektoen Enteric Agar contain what three substances as carbon sources? Why is this significant? |
Lactose, Sucrose, Salicin; salmonella and Shigella species cannot ferment these three sugar carbon sources, but most other enteric scan. Therefore, colonies that can't ferment the sugars to produce acid can't be determined to NOT B salmonella for Shigella.
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You are looking at the results of your Hektoen Enteric Agar plate for a patient with food poisoning and discover yellow/salmon colonies. What does this infer? What is it most likely?
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The colonies can ferment the sugars that act as carbon sources, therefore the colonies cannot contain Salmonella or Shigella. The colony is most likely E. coli, given that it can ferment the sugars, and, along with Salmonella and Shigella, is one of the three most common causes of food poisoning.
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HE plates contain sulfur, which functions as a ________. _______ and _______ species can reduce sulfur to _________ (H2S) HE plates contain ____________, which functions as an indicator. This reacts with _______ to produce a black precipitate (black color on top of the colonies) in colonies that are able to reduce sulfur. |
Substrate; Salmonella, Proteus; hydrogen sulfide gas (H2S)
Ferric ammonium sulfate; H2S; black |
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You're looking at the results of your HE plate, and see that there is a black precipitate over some of your colonies. What does this indicate and why?
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This indicates that the species are most likely Salmonella or Proteus, as the HE plate contains sulfur (substrate), which they can reduce to H2S. The HE plate also contains ferric ammonium sulfate, which reacts with this H2S to form a black precipitate.
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HE plates also contain a pH indicator, ________, so the colonies that ferment sugars that produce acid take on a ______ to _____ color. Colonies that cannot ferment the sugars (ie Salmonella, Shigella, Proteus species) will form ________ colonies, due to their use of ______ as the main carbon source and subsequent production of an _______ environment |
bromthymol blue; yellow, salmon; blue green; protein; alkaline |
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You are looking at the results of your HE plate. You see a blue-green lawn with black precipitate. What can you infer?
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The plate is green, meaning that the colony is alkaline, and use protein as their main carbon source because they can not use the sugars, meaning that it could be Salmonella, Shigella, or Proteus. BUT, there is also a black precipitate, and only Salmonella and Proteus are both able to reduce sulfur, giving the black precipitate. Therefore, we can assume it is either Salmonella or Proteus. |
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You are looking at the results of your HE plate. You see a blue-green lawn with no black precipitate. What can you infer? |
The plate is green, so it must either be salmonella, shigella, or proteus, as they can't ferment the carbon sugars. However, since salmonella and proteus are able to reduce sulfur, and there is no black precipitate, we can assume that this colony is Shigella. |
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In regard to color, your HE plate is yellow. What does this mean? |
It means that your plate has a high acidity, and whatever bacteria is on your streak has the ability to ferment the carbon sugars lactose, sucrose, or salicin (meaning that it can not be salmonella, shigella, or proteus) |
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MAC agar is both selective and differential, T/F
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True
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MAC agar contain ______ and ______ to inhibit the growth of gram ______, therefore it selects for gram ______.
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bile salts, crystal violet, inhibits gram positive, selects gram negative.
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MAC, HE, and EMB all select gram ______ |
negative |
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pH indicator that is red when it has an acidic ph (any pH less than neutral) and is colorless otherwise. In what test does this indicator exist? |
Neutral Red; MAC |
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You're looking at a MAC and the colony is red. What does this indicate? What if the colony is colorless or slightly yellow? |
An acidic pH, meaning that the bacteria has th ability to ferment lactose and produce acid Colorless or slightly yellow = alkaline = can't ferment lactose. |
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MAC agar is usually used to differentiate between subspecies of the Enterobacteriaceae group, based on their ability to ferment lactose, T/F? |
True |
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Sometimes a special recipe of MAC is made without _______, to allow the growth of salt tolerant gram positives such as ________ and _______ |
crystal violet; enterococcus, staphylococcus |
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Staph and Enterococcus are halophilic and gram positive, T/F
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T |
