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MICRO 150 - Lab Exam
Terms in this set (65)
Trypticase Soy Agar
Why are mediums inverted?
So that condensation won't interfere with the bacteria
What is total magnification?
Total magnification = occular x objective
Ex. (10x) x (4x) = total magnification of 40x
Are molds eukaryotic or prokaryotic?
Are yeasts eukaryotic or prokaryotic?
Are bacteria eukaryotes or prokaryotes?
What magnification is oil immersion?
What kind of anaerobe is E. coli?
a facultative anaerobe
What are facultative anaerobes?
Grow with or without oxygen
colony forming units
When are serial dilutions used?
done when there are too many colonies to get into the 25-250 colony range per plate
When is filtration used?
When quantity of bacteria is very small
bacteria grows throughout media
Bacteria grows on surface of media
eosin methylene blue
List 3 reasons why the results of the test tube evaluation of a disinfectant may not accurately reflect its performance in practical application:
1) Temperature - work well at room temperature (NOT cold temperatures)
2) Fresh disinfectant - as disinfectants age they lose their killing power
3) some work against gram (-) bacteria and some work against gram (+) bacteria
In fermentation lab, what were the three necessary things?
1) TSA with sugar (either lactose, sucrose, or glucose)
2) phenol red (indicator)
3) durham tube (captures gas - CO2)
In fermentation lab, what would the color yellow indicate?
In fermentation lab, what would the bubbles indicate?
Presence of CO2
How much ATP does respiration make compared to fermentation?
Respiration: 38 ATP
Fermentation: 2 ATP
What were the types of acids in the fermentation lab?
Pyruvate, lactic acid, and acidic acid
What are neutral in the fermentation lab?
Alcohols, isopropinal, and acetone
What temperature does yeast grow?
37 C (body temperature)
What temperature does mold grow?
25 C (room temperature)
Sabouraud's Dextrose Agar
selects for yeast and fungi (bacteria will not grow); sugar concentrations will go up, pH will go down
can grow as yeast when temperatures are 37 C or molds when temperatures are 25 C
Describe components of fungi
spores - fruiting bodies
hyphae - threadlike structures
mycelium - mass of hyphae
What kind of agar is Mueller Hinton Agar?
Purpose of the Kirby Bauer Method
to find the MIC - minimum inhibitory concentration
to find the minimum antibiotic needed to kill bacteria
disease carried by an animal
If DNA is negative, it will migrate to
What bacteria was used in the epidemiology lab and turns red with heat?
What is the yeast that can grow in the human body?
Is the Sabaraud's Dextrose agar selective, differential or both?
It is selective for fungi and yeast (bacteria will NOT grow)
What method was used in the antibiotics lab?
Kirby Bauer Method
Is Blood agar selective or differential?
NOT selective, differential based on hemolysis
Define beta, alpha, and gamma within the context of Blood agar:
Beta = complete clearing of blood (staph. areus and strep. pyogenes - yellow)
Alpha = partial clearing of blood (strep. pneumoniae - green)
Gamma = no clearing of blood (everything else)
What does the presence of bubbles mean in a catalase test?
means it is catalase + (Staph. areus)
What bacteria is catalase -?
What is used as the determinant in the catalase test?
Is Mannitol Salt agar selective, differential, or both?
It is selective for staphylococcus (because staph grows in high salt concentrations) but the pH indicator makes it also differential
What bacteria ferments mannitol in the mannitol salt agar?
S. areus (yellow)
*anything pink is S. epidermidis
What enzymes causes blood to clot?
Why is nutrient agar used in experiment 1?
Because everything grows on it
Why is the petri dish so suitable for the aerobic cultivate of microorganisms?
1) when inverted, they keep condensation from mixing samples
2) They keep contaminants out
3) Are clear so colonies are easily visible
What is the function of oil when used with the 100x objective?
Prevents scattering of light rays, and increases numerical aperature
Identify the following terms: parfocal and resolution
Parfocal - lens that stays in focus when magnification is changed
Resolution - shortest distance between 2 points on a specimen that can still be distinguished by the observer
Why do you flame the necks of the tubes immediately after uncapping and before replacing caps?
To kill bacteria that may try to get into the tube
How would you know if you contaminated the cultures during transfer?
More than one colony type would be growing, and this would be tested by a gram stain or streaking for isolation
List the points of aseptic technique that should be observed when streaking a plate
Heating the loop between each streak
What kind of dyes are are crystal violet, carbol fuchsin, and methylene blue?
In the negative stain lab, why is it called a negative stain?
Nigrosin is an acidic stain and gives up a hydrogen ion to become negatively charged. The surface of the cell repels the stain. The bacteria will be clear while the background is dark
What are the advantages of differential staining over simple staining of bacterial cells?
Differential staining helps identify different bacterial cells; gram positive or gram negative. Gram positive will stain with the primary stain and gram negative will stain with the counterstain
How does the structure of the bacterial cell wall determine the gram stain reaction?
Gram positive bacteria have a large layer of peptidoglycan and stain purple by crystal violet. Gram negative bacteria have a much smaller layer and do not turn purple because they cannot retain the dye. Gram negative bacteria turn red due to the counterstain, safranin
Did the data from each dilution set reflect a tenfold or hundredfold difference in count as expected?
How might variations in the class results be explained in dilutions?
2) not adding enough drops
Indicate some possible ways in which foods may become contaminated with enteric organisms (bacteria of the intestines):
1) thawing and re-freezing certain produces
2) lack of washing hands of food handlers
3) during commercial processing
4) infected food handlers
5) from other infected food sources
6) using human feces as fertilizer
Explain why it is not advisable to thaw and then re-freeze food products without having cooked them
Staph. aureus can produce toxins at room temperature - freezing does not kill toxins
You transfer 1 ml of stock to 99 ml of saline
1/1+99 = 1/100 = 10-2
You transfer 0.1 ml of stock to 9.9 ml of saline
0.1/0.1+9.9 = 0.1/10 = 1/100 = 10-2
You transfer 100 ml of stock to 900 ml of saline
100/100+900 = 100/1000 = 1/10 = 10-1
You transfer 50 ml of stock to 450 ml of saline
50/50+450 = 50/500 = 1/10 = 10-1
You transfer 0.1 ml of stock E. coli into 9.9 ml of saline in tube 1. From tube 1 you transfer 0.1 ml into 9.9 ml of saline in tube 2. From tube 2 you transfer 0.1 ml into 9.9 ml of saline in tube 3. What is the total dilution in tube 3?
1) 0.1/0.1+9.9 = 0.1/10 = 10-2
2) 0.1/0.1+9.9 = 0.1/10 = 10-2
3) 0.1/0.1+9.9 = 0.1/10 = 10-2
(10-2)(10-2)(10-2) = 10-6
From tube 3 (above) you plate 0.1 ml onto each of 3 plates. After 24hrs of incubation, the average of the 3 plates is 500 colonies. How many bacteria (CFU/ml) are in the original stock culture?
Cell counts from tube 5 = 500 (CFU) per 0.1 ml = 5000 CFU per 1.0 ml = 5 x 10 to the 6 CFU/ml
Total CFU in stock tube = 5 x 10 to the 3/10-3 = 5 x 10 to the 9
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