L19-Microbial Growth Control (26)

Question 1

List the methods of physical sterilization.

Answer 1

heat (autoclave and pasteurization), radiation (UV, ionizing), filtering (depth, membrane)

Question 2

List the methods of chemical sterilization.

Answer 2

• sterilant/sterilizer/sporicide-destroy microbial life and endospores, ex-ethylene oxide, formaldehyde, sodium hypochlorite (bleach) or amylphenol. hospital/lab instruments
• disinfectant-kill micorbes but not always endospores, ex-ethanol on lab bench
• sanitizer-reduce not eliminate, ex.-cooking supplies
• antiseptic-chemical agents that kill/inhibit growth, can be applied to living tissue. ex. ethanol

Question 3

Differentiate between bacteriostatic, bacteriocidal, bacteriolytic.

Answer 3

• bacteriostatic-inhibits growth
• bacteriocidal-kills microbes
• bacteriolytic-kills and lyses cells

Question 4

What are the ways we measure anti-microbial activity?

Answer 4

1) disk diffusion test-measure zone of inhibition

2) minimum inhibitory concentration-incr concentration in test tube culture medium

Question 5

What is/how is the log-fold reduction used?

Answer 5

defn-amount the microbial population has decreased, 1 unit=90% decr, 2 unit=99% decr
Regulatory agencies use “x log” reduction to determine amount of sterilization needed 7-milk, 12-canned goods

Question 6

What is viable but not culturable? How does that present issues when trying to enumerate bacteria?

Answer 6

defn-bacteria that are in a state of very low metabolic activity and do not divide, but are alive and have the ability to become culturable once resuscitated
-poses problems in assessing quality of sample

Question 7

What is the general mechanism by which antibiotics work?

Answer 7

Interruption of one of many cell processes such as cell wall synthesis, folic acid metabolism, DNA gyrase, RNA elongation, protein synthesis, or lipid synthesis

Question 8

Describe: nucleoside analogs, protease inhibitors, influenza antivirals

Answer 8

• nucleoside analogs: inhibit retrovirus multiplication by mimicking part of nucleoside structure/blocking RT (ex. AZT)
• protease inhibits: mimics protein substrate (assembly of new virions) and inhibits proteases
• influenza antiviral-blocks neuraminidase and prevents infl. from leaving the cell, ex tamiflu

Question 9

What is the natural ecological purpose of antibiotics?

Answer 9

To decrease competition for resources. Ex. streptomycin in soil

Question 10

What is selective toxicity?

Answer 10

The ability of a chemical or drug to kill a microorganism without harming its host.

Question 11

Describe the mechanisms of antibiotic resistance.

Answer 11

1. organism lacks structure antibiotic inhibits, mycoplasma-lack cell wall
2. organism is impermeable,, ex-gram neg to penicillin G
3. organism can inactivate-ex. beta lactamase
4. modify target of antibiotic
5. development of resistance biochemical pathway-ex. sulfa drugs/uptake folic acid instead
6. organism pumps out antibiotic via efflux pump

Question 12

How is antibiotic resistance spread?

Answer 12

R-plasmid, also

1) overuse in clinical practice
2) patient noncompliance
3) antibiotics in agriculture (50%)

Question 13

Sulfa drugs- mechanism of action, target and examples.

Answer 13

• mech: inhibit DHPS which blocks folate synthesis
• target: bacteria
• ex: sulfacetamide, sulfonamide

Question 14

Quinolones- mechanism of action, target and examples.

Answer 14

• mech: inhibit DNA gyrase (gram-), topoisomerase (gram +)
• target: broad spectrum bacteria
• ex: ciprofloxacin

Question 15

B lactams- mechanism of action, target and examples.

Answer 15

• mech: block peptide bond formation by transpeptidase in cell wall (NAG-NAM)
• target: gram +
• ex: penicillin, methicillin

Question 16

cephalosporins- mechanism of action, target and examples.

Answer 16

• mech: resist B-lactamase competitively inhibit penicillin binding proteins
• target-gram +
• ex: Cephalosporium

Question 17

aminoglycoside- mechanism of action, target and examples.

Answer 17

• mech: inhibit protein synthesis at 30s subunit of ribosome, interfere with proofreading, and disrupts cell membrane
• target: gram -
• ex:streptomycin

Question 18

tetracyclin- mechanism of action, target and examples.

Answer 18

• mech: bind 30s ribosomal unit and inhibit protein synthesis, easily resisted
• target: gram + and - broad spectrum
• ex: tetracycline