When a mutations result when the bacterium is exposed to a mutagen (a physicl or chemicl agent)
What plate method is used in the bacterial mutation exercise?
Gradient-agar plate method
What is the purpose of the gradient-agar plate method?
To isolate and select streptomycin-resistant mutant staphylococcus aureus strains.
T or F: You observe for the development of resistant S. Ureus colonies in the reas of lower streptomycin concentration.
False: Higher concentration
What is the Kirby-Bauer method used for?
It is used to determine antibiotic susceptibility, using antibiotics impregnated onto paper disks.
What does the zone of inhibition and MIC represent? What does it mean if there is a zone of inhibition? small to no inhibition diamter?
The inhibition zone diameter that is produced will indicate the susceptibility or resistance of a bacterium to the antibiotic.
Zone of inhibition indicates susceptibility
Zones of a smller diameter or no zone at all show that the bacterium is resistant to the antibiotic.
What is being tested for in the presumptive phase in the MPN test? What does a positive result mean?
Durham tubes are used to show gas production in lactose broth tubes
A positive test shows that there are possible coliforms in the tube by a gas bubble present.
What is the purpose of the confirmed test in the MPN test? How is this done?
This is to confirm that there are coliforms in the tube of the positive presumptive test tubes.
After the presumptive test is done, materials are transferred from the highest dilution of those lactose broth tubes that showed growth and gas production into brilliant green lactose bile broth.
These tubes are selective and differential for coliforms, so gas formation is a confirmed test for total coliforms.
How is the completed phase of the MPN done and what is being looked at?
After a positive test is shown in the confirmed phase, plates are streaked onto EMB or Endo plates for isolation. Colonies are then split into 2 tests:
*Before the tests are done, colonies are put into lactose bile broth and streaked on a slant and then incubated*
1. A sample is taken from the slant, and gram stained.
2. The LBB has another Durham tube and is looked at for gas production.
Conclusion: If gas is produced and the bacterium is a gram-negative nonsporing rod, the completed test is positive.
What are actinomytes?
Members of the soil microbial family, including filamentous fungi
What are the three groups of microorganisms being looked for in the soil lab?
In this soil micorganism exercise, match the group of microorganism with the type of media used for them:
1. Actinomycetes ____
2. Bacteria ____
3. Fungi ____
A. Triptic soy agar
B. Sabouraud dextrose agar
C. Glycerol yeast agar
If 200 colonies of soil microorgnism was present on the 10^-7 plate, what would the number of respective micorganisms be per milliliter of orginl culture (gram of soil)?
Answer: 2.0 x 10^9 colonies/gram
What are some physical features of soil that influence microbial populations? (7 possible)
1. Soil fertility
2. Soil moisture
3. Soil temperature
4. Soil aeration
6. Soil PH (H-ion Concentration)
7. Organic matter, Food and energy supply
Why are different dilutions used for bacteria, fungi, and actinomycetes?
Each gram of rich garden soil may contain millions of these micro- and macroorganisms, so dilutions must be made for counting.
Fill in the blank:
The phenol coefficient is calculated by dividing the __a__ dulution of the antimicrobial of interest, which kills organisms after __b__ minutes, but not after __c__ minutes, by the __d__ dilution of phenol that has the same characteristics.
A dilution of phenol at 1/20 kills S. Aureus within 10 minutes.
Another dilution of Lysol kills S. Aureus within 10 minutes as well.
What is the Phenol coefficient?
What is the phenol coefficient of Lysol if no growth occured at 1/450 at 10 minutes, nd growth occured for phenol at 1/90 fter 10 minutes?
PC of Lysol = 450/90 (Lysol dilution/Phenol dilution) = 5