On this page is a set of general review questions forwhich there is presently no posted key.
1. Relevant to just plain, old Common Sense: Technicians Aand B work in a water quality lab. They received a sample of water from theVilas Park Beach and they found that they were out of sterile saline which theyusually use for a diluent, so they used the next best thing on hand: sterileBrain Heart Infusion Broth.
Technician A made decimal (1/10) dilutions of the water sample and theninoculated plates from the dilutions. Technician B did the same, but he gotdistracted and let his first 1/10 dilution sit around for a few hours beforemaking subsequent dilutions and platings.
After incubation of the plates, Technician A got a count of 4.4 X102 CFU/ml and Technician B's count was 4.9 X 106 CFU/ml. Who had the more reliable count of the water sample? Why?
(Note: Both technicians performed specific techniques regardingdilutions, inoculations and incubations correctly. The answer has nothing to dowith those techniques.)
2. Relevant to our enrichment/isolation experiments (9.3, 10.2, 11.1, 11.2, 11.3): Fill in the blanks on the table given here. When we get to other specific groups of bacteria (enterics, coliforms, etc.), the same considerations apply – that is, we can extend the table to accomodate these organisms and fill in the blanks with the relevant items.
3. Relevant to the energy-generating processesdiscussed in Experiments 5.1, 7.1 and 11.1: You should be able tomatch the energy-generating processes in column b with the items incolumn a. (One letter per blank. Some items in column a havemore than one blank.)
Twoprocesses which are responsible for the patterns of growth seen inThioglycollate Medium that help in defining "oxygen relationships."
Twoprocesses which are possessed by the purple non-sulfur photosynthetic bacteria. We set up a test for these (in Experiment 11.1, Period 3) which was similar tothe test for "oxygen relationships."
The process associated with nitratereduction.
Three processes which are associated withanaerobic growth.
The process responsible for creatinganaerobic conditions in our photosynthetic enrichments (and in media overlayedwith mineral oil in the enteric experiment).
A. aerobic respiration
B. anaerobic respiration
D. oxygenic phototrophy
E. anoxygenic phototrophy
4. More about the nature and definitions of "cells" and"colony-forming units": First consider the organism Aerococcusviridans and the characteristic arrangement of its cells. Now, suppose youhad a broth culture in a tube which you vortexed vigorously for a minute or two. Just before and immediately after this vortexing, you made dilution plates todetermine the CFU/ml of the culture. After incubation of the plates, you findthat the pre-vortexing count was approximately 2 X 108 CFU/ml, andthe post-vortexing count was approx. 8 X 108 CFU/ml. As you realizethe number of cells in the culture would not have changed between theinoculations of the two sets of plates, how do you account for the increase inthe count?
5. Relevant to Experiment 11.2 – relating the age of aBacillus culture to the staining and morphological characteristics of thecells: You believe you have isolated a species of Bacillus, andan isolated colony is on a plate which was incubated for two days. What twostaining procedures could you perform on the colony which would help toconfirm your diagnosis? Also, what portion of the colony (centeror edge) would you use for each stain, and why?
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6. Comparing growth curves (which are drawn according to periodiccounts made for broth cultures) and colony development – similar in part tothe above question: You have a colony of Bacillus cereus whichhas been growing for two days on a plate, constantly expanding outward("colonizing new territory") as the vegetative cells continue to grow anddivide. Might various points from the center to the edge of the colonycorrespond to particular points or stages on a growth curve which could be madefor a broth culture of B. cereus? How might this relate to differencesone may see in the gram reaction and presence of endospores between the centerand the edge? (Note: Can one truly say "old" cells and "young" cells? Recallthe introduction to Experiment 1.)
7. Relevant to Experiment 14 and the negative consequences ofbad streaking and isolation: Here is a "faulty diagnosis" question,showing how following correct procedures (such as the minimum aseptic andsafety procedures in Appendix B of the
A patient was admitted with signs of a severe bacteremia (bacterial bloodinfection). Technician A took a blood culture and determined that the cause ofthe infection was a typical Salmonella. The patient was then treated forSalmonella blood infection but did not respond to treatment. Classicsigns of another disease began to appear.
Technician B came in and took another blood culture and correctly determinedthat (1) Salmonella was not present and (2) there were actually twodifferent organisms in the blood, one of which was Yersinia pestis, thecausative agent of plague.
Consider the following table as you answer the questions below. (Note: Maltose, mannose and mannitol are sugars or sugar-like compounds which can befermented by some organisms to produce acid.)
8. Relevant to the most-probable number method and Experiment9: You decide to do a most probable number analysis to enumeratebacteriophages in soil, specifically those which can lyse E. coli strainB. A 1/10 dilution of soil was made, and this suspension was passed through afilter in order to remove microbial cells and soil particles. From the filteredmaterial, two more 1/10 dilutions were made (up through10–3).
From each of these three dilutions, flasks of Nutrient Broth wereinoculated; each flask was inoculated with either 10, 1 or 0.1 ml as shown inthe table below. Immediately following this procedure, each flask wasinoculated with E. coli strain B.
After incubation, the flasks were checked for turbidity (growth of thehost culture), and the results were tabulated as shown in the table below. Fromthese results, what would be the most probable number of plaque-forming units(PFUs) per gram of the soil?
(A hint: What actually constitutes a "positive reaction" in these flasks? Utilize the bottom row of the following table. Figure that out and use the MPNtable accordingly!)
|dilution of soil||10–1||10–2||10–3|
|amount of the dilution inoculated into each of threeflasks||10 ml||1.0 ml||1.0 ml||1.0 ml||0.1 ml|
|number of flasks showing turbidity||0||1||2||3||3|
|number of flasks showing a "positive reaction" can beindicated here, for convenience|
9. Relevant to our phage-infectivity and conjugationexperiments: In Experiment 9.2, we found that the Hfr strain we usedin Experiment 8.2 is resistant to phage JL-1, and the F– strainis sensitive to the same phage strain. If we were to find the opposite to holdtrue regarding another phage strain (we can call it JL-2), how could we set upan experiment to demonstrate the result of conjugation and recombinationinvolving the transfer of phage resistance genes from the Hfr strain to theF– strain? Recall what was done in Experiment 8.2. Included inyour experiment would be a consideration of the selective medium we woulduse to detect the desired recombinants.
10. Relevant to dilution plating and Experiment 15: Isthis set-up OK?
11. Relevant to dilution plating and Experiment 15: Consider the following set-up, and again recall our old definitions (fromAppendix C) of "dilution factor" and "plated dilution."
12. Relevant to differential media and Experiment 17: Foryour Experiment 17 unknown, you find you have two colony types (=2different gram-negative rods) on your MacConkey plates, and you need tofind your third unknown. Looking at the colonies on your HIA plates, howwould you go about finding your third unknown?