6-4: Control of Microbial Growth (and death) Flashcards
What is decontamination/disinfection?
Neutralizing or removing microbes. Goal is to reduce numbers of potentially harmful organisms
What is sterilization?
Process of killing all microbes. Either sterile (no microbes) or not
What is decimal reduction time
Amount of time it takes to reduce number of microbes by a factor of 10 at a given temperature
What is thermal death time? What does it depend on?
Amount of time it takes to kill all cells at a given temperature. Depends on the number of cells
What do decimal reduction time/thermal death time both depend on?
pH, [salt], moisture (dry heat not as effective as wet heat), presence of fats/sugars/proteins (can decrease heat penetration)
What are autoclaves
Used to sterilized objects in healthcare, research using steam. Water is pressurized to increase the boiling temperature to 121 degrees, typically for 15 minutes.
What temperature is required to kill endospores using autoclaves
121C for 15 minutes
What is pasteurization
Food is heated for specific amount of time to eliminate pathogens and reduce spoiling agents (eg. non pathogenic bacteria, enzymes)
What causes milk to spoil
Heat-resistant lactic acid bacteria that survive pasteurization
What temp is milk pasteurized at
71C for 15 seconds
What is the difference between UV light and ionization radiation?
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
What is filtration
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).
What are some ways that disinfectants, sanitizers and antiseptics use to control chemical growth?
Membrane disruption, protein denaturation, oxidizing agents
What are sterilants? Give an example.
Kill all microbes e.g. formaldehyde
What are disinfectants? Give an example.
For surfaces, kill many/most but not all (eg. not endospores) e.g. lysol
What are sanitizers? Give an example.
Less harsh to humans, generally less effective e.g. soaps
What are antiseptics? Give an example.
Kill or inhibit growth of microbes, non-toxic enough to use on tissues/wounds e.g. ethanol
What is an antimicrobial agent
Chemical that kills or inhibits microbial growth
What is the difference between bactericidal, bacteriostatic, and bacteriolytic.
Cidal = kill cells
Static = inhibit growth, microbe not dead and can recover
Lytic = kills cells and cause them to lyse (no longer observable)
What is the minimal inhibitory concentration of a compound
Lowest concentration of a compound that fully inhibits growth
How is MIC determined?
Using serial dilutions of the compound and measuring when there is a complete lack of microbial growth.
How can solid media be used to measure chemical toxicity?
Solid media with antimicrobial disk placed on it, measuring zones of inhibition. Eg. Kirby-Bauer Test
What are antibiotics
Medicines/molecules with antimicrobial properties used to treat infections.
Specific mechanisms to target specific aspect of microbial biology that is absent/different in humans
Who discovered the first true antibiotic? How?
Alexander Fleming (penicillin). Discovered from a mold that was secreting a compound that kills bacteria.
Aside from penicillin, what else did Alexander Fleming discover?
Lysozymes
What was the first true antibiotic used in clinic?
Prontosil, an inihibitor of folate biosynthesis. It is a produg and only works in animal models, not in vitro.
How do antibiotics work?
Target essential processes such as cell wall biosynthesis, translation, DNA replication, essential biosynthetic processes.
What is an important issue in ensuring that antibiotics work?
Most have intracellular targets, so permeability can be an issue.
What is the target of penicillin? What does it do?
Inhibits penicillin binding protein activity, which catalyzes the transpeptidation reaction that crosslinks the cell wall.
What is the mechanism of action of penicillin?
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.
What Actinomycetes soil-dwelling bacteria produce a large number of antibiotics?
Streptomyces
What are Streptomyces?
Soil dwelling bacteria that produce large numbers of antibiotics - have large genomes with interesting biosynthetic gene clusters.
How is antibiotic resistance a problem
Drugs that were once effective against pathogens unusable due to high resistance
Running out of options to treat MDR pathogen strains
What is the most common mechanism by which antibiotic resistance is required?
Acquiring antibiotic resistance genes via horizontal gene transfer
What are the four mechanisms of antibiotic resistance?
- Modification of drug target (enzyme mutation)
- Enzymatic inactivation of the drug (degrading the drug)
- Preventing access to bacterial cell (efflux pump)
- Metabolic bypass (find another way to do what the drug is blocking)
How is persistence different than resistance>
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.
Name one common route of persistence.
Dormancy (slowing/shutting off metabolism). Works since lots of antibiotics depend on metabolic activity/growth in order to work.
