Week 10 Review

Question 1

Compare and contrast sterilization, commercial sterilization, and disinfection.

Answer 1

Sterilization: kill all living organisms

Commercial sterilization: eliminate spoilage and disease-causing organisms in food

Disinfection: kill vegetative (non-spore) cells

Question 2

Describe the stages of a bacterial growth and death curve. How are death and growth curves alike?

Answer 2

Lag Phase: bacteria are adapting
Exponential (Log) Phase: bacterial growth occurs at an exponential rate
Stationary Phase: balance between cell division and cell death
Death Phase: the number of viable bacterial cells declines rapidly

Both are influenced by environmental factors such as temperature, pH, nutrient availability, oxygen levels, and the presence of inhibitors or antimicrobial agents.

Question 3

What type of graph is used to measure microbial growth and death? Why is it used?

Answer 3

Logarithmic graph, visualize and analyze microbial populations’ exponential growth or decline over time.

Question 4

What factors influence the effectiveness of control agents?

Answer 4

Number of microbes you are trying to kill
Environmental influences (blood, vomitus, feces, biofilms)
Microbial characteristics
Time of exposure
Physical/chemical control methods

Question 5

What are the actions of control agents (i.e. how do they work)?

Answer 5

Alternation of membrane permeability
Damage to proteins and nucleic acids
Breaking H bonds, disulfide bridges -> protein structure lost (denaturation)

Question 6

What are the physical methods of control of growth? Describe each method and give examples.

Answer 6

Temperature (heat/low temp)
Heat: varies in microbes
Thermal death point: lowest temperature which kills all microbes in 10min
Thermal death time: minimum amount of time that kills all microbes
Moist sterilization: boiling kills most pathogens in 10mins
Autoclave: high pressure (100kPa) + high temp (100C) = 121C 15 min, used to sterilize culture media, lab/surgical equipment
Pasteurization: reduce spoilage organisms and pathogens
- 63C for 30min, high-temp short time: 72C for 15sec, ultra-high-temp: 140C for <1 sec
Dry heat: kills by oxidation (flaming, incineration, hot-air sterilization: 170C, 2 hours)
Low temp: Inhibits microbial growth (refrigeration, deep-freezing, lyophilization: freeze drying)

Radiation
Ionizing (X-rays, gamma rays, electron beams): damages DNA
Nonionizing (UV, 260nm): damages DNA
Microwaves: kill by heat, not specially antimicrobial

Filtration
High-efficiency particulate air: removes microbes >0.3um diameter in air
Membrane filers: remove microbes >0.1um diameter in liquid

High pressure: denatures proteins

Desiccation: causes plasmolysis (cells lose water/shrink/die via osmosis)

Question 7

What are the chemical methods of control of growth? What do they depend on?

Answer 7

Disinfectants: nonliving tissue
Used on inanimate objects

Antiseptics: living tissue
Used on skin

Question 8

Give examples of each disinfectant. How do they work? Give examples.

Answer 8

Phenols and phenolics: Interrupt plasma membrane, making it more permeable
- Phenol: rarely used
- Phenolics: chemically alters phenols
- Injure plasma membrane, cell wall of mycobacteria (O-phenyl phenol)

Bisphenols: Two phenyl groups w/ bridge
- Disrupt plasma membrane (hexachlorophene (hospital), triclosan (widely used, inhibits enzymes used for fatty acid synthesis)

Alcohols: Denatures proteins and dissolves lipids (ethanol, isopropanol)

Heavy metals
- Oligodynamic action: small amounts of antimicrobial activity
- Protein denaturation (silver, copper)

Question 9

What are chemotherapeutic agents? What should they ideally kill and not harm?

Answer 9

Chemotherapeutic agents: selectively interfere with microbial growth
- Ideal kills pathogens w/o hurting host (antibiotics/synthetics)

Question 10

What is the history of the chemotherapeutic agents? Name the scientists and their contributions.

Answer 10

Paul Erlich
- Used salvarsan to treat syphilis (localized)
- First synthetics: sulfonamides (treated systematically)

Alexander Fleming
- Found Penicillin notatum inhibits S. aureus
- Isolated as penicillin (first antibiotic)

Selman Waksman
- Isolated streptomycin from Streptomyces sp.
- Antibiotics: compounds produced by microorganisms that inhibit the growth of other microorganisms

Question 11

How does the number of antimicrobial drugs differ for bacterial, fungal & protozoan, and viral infections? What is the reason for these differences?

Answer 11

Bacterial infections: variety of drugs
- Lots of differences between eukaryotes/prokaryotes

Fungal/Protozoan infections: More difficult
- Physiology similar to eukaryotic cells

Viral infections: Even more difficult (infects host cell)
- The cellular physiology of the pathogen is the same as the host

Question 12

How does effectiveness differ between narrow and broad-spectrum antimicrobial drugs? What are the advantages and disadvantages of each?

Answer 12

Narrow:
Effectiveness: limited no. microbes
Advantage: less damage to normal flora, less selection for resistance
Disadvantage: must ID agent

Broad:
Effectiveness: wider range of microbes
Advantage: don’t need to ID
Disadvantage: destroy native flora/select for resistant pathogens

Question 13

What are the 5 main targets of antibacterial drugs? Describe how each method works and give examples.

Answer 13

Cell wall
- B-lactams (penicillins/cephalosporins, share B-lactam structure) inhibit peptidoglycan synthesis
- Modifications allow increased target range
- Bacitracin (topical ointments): interferes w/ cell wall synthesis
- Vancomycin (glycopeptide antibiotic): useful for treating S. aureus resistant to B-lactams
- Enterococcus faecium resistant to vancomycin (VRE)

Ribosomes
- Chloramphenicol, macrolides, and lincosamides: bind 50S subunit, prevent peptide bond formation, stop protein syn.
- Aminoglycosides: bind to 30S subunit, impair proofreading, resulting in the production of faulty proteins
- Tetracyclines: bind to 30S subunit, block binding of tRNAs, inhibiting protein synthesis

DNA/RNA synthesis
- Rifamycins (Rifampin): inhibit RNA synthesis
- Treat TB, prophylactic for meningitis
- Quinolones/fluoroquinolones: inhibit DNA replication
- Norfloxacin/ciprofloxacin wide use

Metabolic pathways: sulfonamides/Sulfa drugs = competitive inhibitor of enzymes involved in folic acid synthesis

Plasma membrane
- Polymyxins (polymyxin B, colistin)
- Lipopeptide (daptomycin)

Question 14

How is susceptibility/resistance determined for antimicrobial drugs?

Answer 14

Kirby-Bauer
- Mueller Hinton plates
- Lawn of bacteria
- Antibiotic discs
- Measure clearing

Question 15

What are the mechanisms of resistance?

Answer 15

Efflux pump (pump antibiotic out)

Blocked penetration (block antibiotic entering)

Inactivation of enzymes (prevent antibiotic function)

Target modification (prevent antibiotic binding)

Question 16

Name the types and examples of antifungal, antiviral, and antiprotozoan drugs.

Answer 16

Antifungal: Amphotericin B: target ergosterol, increase membrane permeability for fungi only

Antiviral: Nucleoside analogs
- Acyclovir is an analog for guanosine (G), limits the severity of Herpesvirus reactivation

Antiprotozoan: Quinine, chloroquine (synthetic): malaria

Question 17

What factors accelerate drug resistance?

Answer 17

Inappropriate use

Overuse

Subtherapeutic does

Patient noncompliance

Question 18

How are antibiotic-resistant bacteria naturally selected?

Answer 18

Only high-level resistance bacteria are left in the final population
- Low resistance is killed by antibiotics

Question 19

What are two ways that resistance is developed? What role do mutations and plasmids play in developing resistance?

Answer 19

Mutations:
Spontaneous mutation rate: 1/10^-6
- Methicillin-Resistant S. aureus (MRSA): change in DNA sequence of plasmid, new low-affinity penicillin-binding protein

Plasmids: self-replication, circular DNA, not part of chromosome
- Naturally occurring
- Resistance (R) and/or Conjugative (help spread)
- Can mutate and transpose
Ex: mutations and transposons (jumping genes) can lead to multi-drug resistance
- A single plasmid can carry the genes to resist many different antibiotics

Question 20

What is the most common horizontal gene transfer method to transfer resistance?

Answer 20

Conjugation: resistance genes can be transferred between germs when they connect

Question 21

What are the different mechanisms of resistance? How does each work? What organisms are usually involved? Give examples.

Answer 21

Inactivation of enzymes or drugs: Gram -/+
Enzymes: Result is decreased affinity of drug to its target (aminoglycosides modifying enzymes change target side so it can no longer bind antibiotic)
Antibiotics: modifies the drug (B-lactamase destroys B lactams (penicillin))

Target modification: Gram -/+
Plasmids/transposons:
- Tet resistance in Streptococcus and Campylobacter sp.
- Bacteria make Tet proteins that dislodge Tet on ribosome
Mutation of enzymatic alteration of target sites
- MRSA modifies penicillin-binding proteins which are involved in getting penicillin into cell

Efflux pump: Gram -
- Found in bacteria to remove toxic substances
- Encompasses practically all classes of antibiotics

Blocked penetration: Gram - (E.coli, P. aeruginosa)
- B-lactams, tetracyclines, some fluoroquinolones
- Examples are modification of porins (pore-forming proteins, typically allow amino acids/antibiotics to diffuse into cells)