Lab questions - BIOS 313 lab PDF

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Kyler Mercado Lab Questions Section 3 Z1766175 P. 39 Source Staphylococcus epidermidis on NA slant Staphylococcus epidermidis in NB Staphylococcus epidermidis on sterile NA plate

Nutrient broth ++

Nutrient agar slant Cloudy, abundant growth

++

White spots were grown

+

NA

P. 40 3. Did you notice a difference in density (turbidity) of growth in NB tubes and NA slants? Suggest possible reasons why a difference might occur. Yes, there was a difference in turbidity of growth in the NB tubes and NA slants. This could be because the nutrient broth is able to allow the bacteria to grow in large numbers for study. The NA slant is used for growing stock cultures and does not produce as many. 4. Did you notice a difference in density of growth on NA slants inoculated from NA slants and NB? Suggest possible reasons why a difference might occur. Yes, there was a difference of growth. This could be because of the nutrients available within the NB tubes and the NA slants. P. 47 1. Preform a quadrant streak on the “practice plate”.

P. 48 3. Did you achieve isolation using the quadrant streak? If so, in which streak did it occur? If you did not achieve isolation, what might you do differently next time? Yes, isolation was achieved, and it was achieved in the second streak as the cells formed an isolated colony. P. 53 Table 1 Organism E. coli S. marcescens

Plate with isolation Third plate Third plate

Comments Formed individual colonies separate from S. marcescens Formed individual colonies separate from E. coli

1a/b. Which plate did you first obtain isolation with E. coli? S. marcescens? First achieved isolation on plate 3 for both E. coli and S. marcescens. 1c. Do you have reason to believe that they should become isolated on the same dilution plate? Why or why not?

Yes, there is reason to believe because by the fourth plate the mixture of the two bacteria is so diluted that the organisms are able to separate themselves which is reflected on the third dilution plate. P. 54 2. Once you obtained isolation at a particular dilution, did you continue to have isolation on subsequent dilution plates? Is this what you would expect? Why or why not? Isolation occurred on the final plat, but yes it would be expected to continue to be isolated as the dilution would only increase from then on. 3. What is the primary negative consequence of not spreading the inoculum evenly over the agar surface? The bacteria would be less likely to form individual colonies or none at all. 4. To get isolated colonies on a plate, only about 300 cells can be in the inoculum. What will happen if the cell density of the inoculum significantly exceeds this number? There will be no isolation of colonies on the agar plate. P. 87 Specimen E. Coli L. lactis

Nutrient Broth 3 2

BHI 1 2

Glucose Salts 1 0

S. epidermidis 1

3

0

B. subtilis

0

0

0

Interpretation Least fastidious Moderately fastidious Moderately fastidious Most fastidious

P. 89 3. What does comparing the growth of a given organism in the three media tell you? In this exercise we gained more knowledge about the media that the organisms were growing in. This was done by transferring different bacteria into different media and observing their growth in that environment and the nutrients it provides. P. 90 6. Which medium supports growth of the widest range of organisms? The BHI media because it had the most growth within each tube compared to the others. Which medium supports the fewest organisms? The glucose salt medium because only E. coli had minor growth while all the others had no growth. 7. Which organism appears to be the most fastidious? How can you tell? B. subtilis appeared to be the most fastidious as it grew the least in any of the media. Which organism appears to be the least fastidious? How can you tell? E. coli appeared to be the least fastidious as it grew in all of the media provided. P. 256 4. In your own words, what is the role of sodium chloride in MSA and how does it work?

Sodium chloride makes the medium selective because its high salt concentration kills most bacteria. This works by the salt dehydrating the bacteria. 5. In your own words, what are the roles of mannitol and phenol red in MSA. The role of mannitol is to provide a substrate for fermentation which will make the medium differential and therefore able to isolate specific organisms. Phenol red is used in MSA is used to indicate the levels of pH throughout the media. P. 255 Organism Growth (N/P/G) MSA growth Interpretation Presumptive color ID S. aureus G yellow Organism not inhibited by NaCl. Staphylococcus E. coli P red Organism inhibited by NaCl. Not Staphylococcus S. epidermis P red Organism inhibited by NaCl. Not Staphylococcus P. 269 Table 1. Organism Enterobacter aerogenes Enterococcus faecalis Escherichia coli E. tythinurium

Interpretation and presumptive ID

Growth (N/P/G) EMB Growth Color EMB G Dark purple

Possible coliform

P

Pink

Gram positive

G P

Green Pink

Possible coliform Gram positive

P. 270 4. In your own words, what are the roles of eosin Y and methylene blue in EMB agar? Eosin Y and methylene blue are dyes that inhibits gram positive bacteria and will allow gram negative bacteria to grow. They also react with lactose fermenters that will have a dark growth. 5. In your own words, what is the role of lactose in EMB agar? Lactose adds to the differential media because it is the substrate of the fermentation. If the organism does not have the ability to ferment lactose to acid end products, then it will not grow....