6-4: Control of Microbial Growth (and death)

Question 1

What is decontamination/disinfection?

Answer 1

Neutralizing or removing microbes. Goal is to reduce numbers of potentially harmful organisms

Question 2

What is sterilization?

Answer 2

Process of killing all microbes. Either sterile (no microbes) or not

Question 3

What is decimal reduction time

Answer 3

Amount of time it takes to reduce number of microbes by a factor of 10 at a given temperature

Question 4

What is thermal death time? What does it depend on?

Answer 4

Amount of time it takes to kill all cells at a given temperature. Depends on the number of cells

Question 5

What do decimal reduction time/thermal death time both depend on?

Answer 5

pH, [salt], moisture (dry heat not as effective as wet heat), presence of fats/sugars/proteins (can decrease heat penetration)

Question 6

What are autoclaves

Answer 6

Used to sterilized objects in healthcare, research using steam. Water is pressurized to increase the boiling temperature to 121 degrees, typically for 15 minutes.

Question 7

What temperature is required to kill endospores using autoclaves

Answer 7

121C for 15 minutes

Question 8

What is pasteurization

Answer 8

Food is heated for specific amount of time to eliminate pathogens and reduce spoiling agents (eg. non pathogenic bacteria, enzymes)

Question 9

What causes milk to spoil

Answer 9

Heat-resistant lactic acid bacteria that survive pasteurization

Question 10

What temp is milk pasteurized at

Answer 10

71C for 15 seconds

Question 11

What is the difference between UV light and ionization radiation?

Answer 11

UV = damages DNA and lethal to microbes at high intensities, sterilize surfaces/air, but low penetration

Ionizing R = gamma rays, improved penetration , used to sterilize surgical supplies, labware, even food

Question 12

What is filtration

Answer 12

Passing liquids through filters with pore size of ~0.2 microns to “sterilized”.
Not as reliable as autoclaving, but does not cause damage like heat (which will damage protein).

Question 13

What are some ways that disinfectants, sanitizers and antiseptics use to control chemical growth?

Answer 13

Membrane disruption, protein denaturation, oxidizing agents

Question 14

What are sterilants? Give an example.

Answer 14

Kill all microbes e.g. formaldehyde

Question 15

What are disinfectants? Give an example.

Answer 15

For surfaces, kill many/most but not all (eg. not endospores) e.g. lysol

Question 16

What are sanitizers? Give an example.

Answer 16

Less harsh to humans, generally less effective e.g. soaps

Question 17

What are antiseptics? Give an example.

Answer 17

Kill or inhibit growth of microbes, non-toxic enough to use on tissues/wounds e.g. ethanol

Question 18

What is an antimicrobial agent

Answer 18

Chemical that kills or inhibits microbial growth

Question 19

What is the difference between bactericidal, bacteriostatic, and bacteriolytic.

Answer 19

Cidal = kill cells
Static = inhibit growth, microbe not dead and can recover
Lytic = kills cells and cause them to lyse (no longer observable)

Question 20

What is the minimal inhibitory concentration of a compound

Answer 20

Lowest concentration of a compound that fully inhibits growth

Question 21

How is MIC determined?

Answer 21

Using serial dilutions of the compound and measuring when there is a complete lack of microbial growth.

Question 22

How can solid media be used to measure chemical toxicity?

Answer 22

Solid media with antimicrobial disk placed on it, measuring zones of inhibition. Eg. Kirby-Bauer Test

Question 23

What are antibiotics

Answer 23

Medicines/molecules with antimicrobial properties used to treat infections.
Specific mechanisms to target specific aspect of microbial biology that is absent/different in humans

Question 24

Who discovered the first true antibiotic? How?

Answer 24

Alexander Fleming (penicillin). Discovered from a mold that was secreting a compound that kills bacteria.

Question 25

Aside from penicillin, what else did Alexander Fleming discover?

Answer 25

Lysozymes

Question 26

What was the first true antibiotic used in clinic?

Answer 26

Prontosil, an inihibitor of folate biosynthesis. It is a produg and only works in animal models, not in vitro.

Question 27

How do antibiotics work?

Answer 27

Target essential processes such as cell wall biosynthesis, translation, DNA replication, essential biosynthetic processes.

Question 28

What is an important issue in ensuring that antibiotics work?

Answer 28

Most have intracellular targets, so permeability can be an issue.

Question 29

What is the target of penicillin? What does it do?

Answer 29

Inhibits penicillin binding protein activity, which catalyzes the transpeptidation reaction that crosslinks the cell wall.

Question 30

What is the mechanism of action of penicillin?

Answer 30

In growing bacteria, the cell wall is constantly being remodelled using autolysin proteins. Penicillin prevents the digested cell wall from being repaired, causing the cell wall to lose integrity and lyse.

Question 31

What Actinomycetes soil-dwelling bacteria produce a large number of antibiotics?

Answer 31

Streptomyces

Question 32

What are Streptomyces?

Answer 32

Soil dwelling bacteria that produce large numbers of antibiotics - have large genomes with interesting biosynthetic gene clusters.

Question 33

How is antibiotic resistance a problem

Answer 33

Drugs that were once effective against pathogens unusable due to high resistance
Running out of options to treat MDR pathogen strains

Question 34

What is the most common mechanism by which antibiotic resistance is required?

Answer 34

Acquiring antibiotic resistance genes via horizontal gene transfer

Question 35

What are the four mechanisms of antibiotic resistance?

Answer 35

1. Modification of drug target (enzyme mutation)
2. Enzymatic inactivation of the drug (degrading the drug)
3. Preventing access to bacterial cell (efflux pump)
4. Metabolic bypass (find another way to do what the drug is blocking)

Question 36

How is persistence different than resistance>

Answer 36

Persistence is when antibiotic-sensitive populations of bacteria include rare cells than are transiently tolerant to antibiotics. These cells are genetically unchanged, can be killed after emergence from tolerant state.

Question 37

Name one common route of persistence.

Answer 37

Dormancy (slowing/shutting off metabolism). Works since lots of antibiotics depend on metabolic activity/growth in order to work.