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Lecture 14

NURS 364 Lecture Notes - Lecture 14: Minimum Inhibitory Concentration, Serial Dilution, Antimicrobial Resistance

Course Code
NURS 364
Deborah Van Kuiken

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Microbiology (BIOL201) Study Guide for Test 3: Can you…?
For all exercises
• Define all the bold terms in each exercise.
• Describe the protocols for each exercise, including the purpose of each step
• Know all given background material, including homework assignments, and additional material
provided in class.
Exercise 19: Physical Means of Control: Ultraviolet Radiation
• Identify the different wavelengths of light and their effects on cells UVA, UVB, UVC. UVA- can be
protected by it fairly easily, doesn’t really cause any damage. UVB- use sunscreen to protect from can
cause damage to endothelial cells on surface of skin. UVC- most dangerous can cause damage to deeper
tissues below skin
• Explain the logic behind tests that kill bacteria in order to evaluate carcinogenicity the more resistant
the bacteria are to death the more carcinogenic they are
• Interpret the growth of microbes after UV exposure in terms of both decontamination effects and
potential carcinogenicity
• Explain why not all bacteria are killed by UV light (there is more than one reason)
Either they had a mutation (already present in genome not caused by UV exposure) or they had
Exercise 20: Chemical Means of Control: Disinfectants and Antiseptics
• Evaluate the effectiveness of disinfectants and antiseptics based on the growth of microbes after
exposures the less microbes that grow after exposure the more effective… greater the zone of inhibition
the better
• Connect the time of exposure to efficacy of the control method
• If present, be able to identify the minimum inhibitory concentration (MIC)
Minimum amount of solution required to inhibit growth of bacteria… in serial dilution it’s the first tube
in which microbes didn’t grow
• Explain how to do a serial dilution
Put 100% (10ml of substance) in first tube then take 50% (5ml) of the substance in the first tube and add
it to the 5ml of water in the 2nd tube. Then take 5 ml of the solution in the second tube and add it to the
5 ml water in the 3rd tube. Then take 5 ml of that solution and add it to the 5ml of water in the 4th tube.
Therefore, you would have concentrations of 100%, 50%, 25%, and 12.5% respectively.
• Be able to describe how we determined the effectiveness of your antimicrobial agent
The larger the zone of inhibition the more effective it was
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Exercise 21: Chemical Means of Control: Antimicrobial Drugs
• Measure the zone of inhibition around various antibiotic disks and determine which organisms are
most susceptible (sensitive) or most resistant (least sensitive)?
Most susceptible = greater zone of inhibition…. Less susceptible= smaller zone of inhibiton
• Explain why some antibiotics may work on some bacteria while others may not.
Antibiotics target specific enzymes of bacterial cell walls and some bacteria have it while others don’t
therefore some bacteria are affected while others are not
• Discuss why antibiotic resistance is a serious concern, how it can develop, and methods to avoid it
It’s a serious concern beause we aren’t making new antibiotics at like all because it’s hard and we’ve
already made a lot so if bacteria build up rsistance to antibiotics they are harder to get rid of and cause
more serious affects.
It can develop by overuse of antibiotics, misuse of antibiotics etc.
Avoid it by taking the full course of you antibiotic prescribed, don’t share anitibiotics , try to fight things
off naturally for a while before getting an antibiotic, use the correct antibiotic for the infection at hand
• Discuss why two antibiotics with the same zone of inhibition are not necessarily equally effective.
Antibiotics have different diffusion rates therefore sometimes when comparing zone of inhibitons
results can be misleading
• Explain why we used Mueller-Hinton agar.
• What is happening when there are a few scattered colonies in your zone of inhibition?
The bacteria may have been spore forming and came back after the antibiotic had run its course or they
could be mutated and resistant.
Exercise 22: Epidemiology
• Explain (broadly) how epidemiologists collect data and the purpose of disease clusters
• Given a table of results from an epidemiology exercise, determine the first two people infected
Who is patient 0…. If someone sick came in contact with someone and they didn’t get sick they aren’t
patient 0
• Discuss the role of vaccines and herd immunity in protecting us from epidemics. Include in your
explanation a discussion of the most vulnerable people, and public health trends that may affect the
vaccination rate.
Vaccines help eliminate or reduce incidences of infections. Herd immunity is when 95% of the
population is vaccinated or immune to the disease/ infection and the other 5% are not but since the vast
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