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Characteristic Growth Pattern in Static closed system
- Lag phase: getting used to the new environment
- log/exp growth phase
- stationary phase
- death or log decline phase (if no breakdown, turbidity remains the same)
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Continuous Culture
- Chemostat / Bioreactor
- can grow infinitely
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Inoculum
Introduction of microbes into medium
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Measuring Microbial Growth
- Direct Measurements: Microscopically total count; dilute + plate + colony count
- Indirect Measurements: turbidity; Metabolic activity
- Total Counts
- Viable Counts
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Actions of Microbial Control Agents
- • Alternation of membrane permeability
- • Damage to proteins
- • Damage to nucleic acids
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Sterilization
Removal of all microbial life, including endospores
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Autoclave
- Moist heat/Steam sterilization
- Kills vegetative cells and spores.
- Good for utensils and liquids.
- Might affect heat sensitive biological compounds
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Moist Heat/Boiling!
- • Boiling water kills bacteria in the vegetative stage.
- • Used for cooking and canning of food.
- • Boiling doesn't sterilize food, but does reduce the number of disease-causing micro-organisms to a level that is not dangerous
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Dry Heat/ Oven
- Samples are placed into a hot air oven for 120 min at 160 C.
- Kills vegetative cells and spores.
- Good for heat-stable items, but not liquids.
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Dry Heat/Flaming
done to loops and straight-wires in microbiology labs.
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Pasteurization
- reduces microbial load, reduces spoilage, increases shelf life, and maintains most of the food composition.
- • 63°C for 30 min.
- • High-temperature short-time 71°C for 15 sec.
- • Ultra-high-pasteurization: 140°C for <1 sec.
- • Thermoduric organisms survive; won't kill spores.
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Filtration Sterilization
- • Could be used to sterilize heat sensitive liquids and gases.
- • 0.2um (common size1x0.5; for viruses, use 0.02um)
- • HEPA filter- High-Efficiency Particulate Arresting filter (0.3um).
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Radiation
- • Radiation damages DNA
- • Ionizing radiation (X rays, gamma rays)
- • Nonionizing radiation (UV)
- • Microwaves kill by heat; not very antimicrobial
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UV Radiation
- Causes modification of DNA by cross-linking DNA.
- Used to decontaminate surfaces and materials that do not absorb light, such as air and water.
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Ionizing radiation
- -X rays
- -Gamma rays
- High energy that produces ions and reactive particles, which can alter DNA, lipids, proteins and spores.
- Used to penetrate solid or light-absorbing materials
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Low temperatures and freezing inhibit growth, but
does not kill microorganisms.
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Biocide/Germicide:
Kills microbes.
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Sterilization:
Removal of all microbial life.
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Sanitization:
Lower microbial counts.
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Disinfectants:
substances that are applied to nonliving objects to remove pathogens.
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Antiseptics:
substances that are applied to living surfaces such as skin to to remove pathogens.
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Antibiotic:
Substance produced by one microorganism that can destroy or inhibit the growth of other microorganisms.
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Antibacterial
a compound or substance that kills or slows down the growth of bacteria.
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Bactericidal:
Substance that can kill bacteria.
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Bacteriostatic:
Capable of inhibiting the growth of a bacteria. some bactericidal sub becomes bacteriostatic at low concentration.
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Joseph Lister
- antiseptic surgery
- promoted the idea of sterile surgery.
- Used carbolic acid (phenol) to sterilize surgical instruments and to clean wounds
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Chemical Antiseptics and Disinfectants
- Alkylating agents: Ethylene oxide, aldehyde
- Heavy metals
- Alcohols
- Halogens
- Phenols and derivatives
- Oxidants
- Detergents
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Ethylene oxide
- Used as gas vapor.
- sterilize heat sensitive equipment and drugs.
- Efficient but limited use: Flammable, explosive and carcinogenic.
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Aldehydes
- • Inactivate proteins by cross-linking with functional groups (–NH2, –OH, –COOH, —SH).
- • Glutaraldehyde and formaldehyde.
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Heavy metals
- Mercury
- Silver
- Zinc
- Copper
- Denature proteins and enzymes by binding to reactive groups resulting in their precipitation and inactivation.
- Mercury containing compound used as antiseptic.
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Alcohols
- Denature proteins and dissolves lipids by acting on cell membranes.
- Pure alcohol is less effective as it will dehydrate a cell but will not kill it. Rehydration could resume viability.
- Usually used at 70% concentration (30% water).
- 60-95%, >=10sec, kills S. pyogenes
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Halogens
- Iodine: Povidone iodine. To clean skin before surgery with soap -> alcohol -> iodine (red).
- Chlorine: Used in swimming pools, water treatment units, and bleach.
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Phenols and derivatives (Phenolics)
- Phenol: mouth rinses (Listerine), Lysol
- Triclosan: anti-bacterial soap
- Disrupt plasma membranes
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Oxidants
- Hydrogen peroxide (H2O2)
- Kills bacteria at 3-6%.
- Kills spores at 10-25%.
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Detergents - Surface-Active Agents or Surfactants
- Dissolve membranes.
- QACs
- SDS: Most common ingredient in toothpaste.
- Chlorhexidine: in mouth rinses.
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Antimicrobial Agents Selective toxicity
a drug that kills bacteria without damaging the host: Therapeutic index
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First synthetic chemotherapeutic agents w/ Selective toxicity
- Salvarsan ( compounds “606”) by Paul Ehrlich
- treat syphilis
- Arsenic based compound (toxic disrupts ATP production).
- Difficult and painful to inject.
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Growth Factor Analogs
- synthetic metabolic inhibitors
- sulfa drugs, isoniazid, and nucleic acid analogs
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Sulfa Drugs - Sulfanilamide
- Gerhard Domagk
- The first widely used growth factor analogs that specifically inhibit the growth of bacteria
- analog of a part of the vitamin folic acid (a nucleic acid precursor), blocks folic acid synthesis, inhibits nucleic acid synthesis.
- Broad spectrum
- effective on bacteria, which synthesize folic acid, but not humans who obtain folic acid from their diet.
- Resistant mechanism: Obtain folic acid from the environment/host
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Nucleic acid analogs
- Blocks nucleic acid synthesis.
- Used to treat viral and fungal infections.
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Quinolones and Fluoroquinolones (Ciprofloxacin)
- Blocks and inhibits DNA gyrase (unwinds DNA) - DNA replication is stopped.
- Broad-spectrum.
- Used to treat urinary tract infections, penicillin resistant anthrax, and TB.
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Mechanisms of Resistance to Quinolones
- • Decrease intracellular quinolone concentration by efflux pumps.
- • Plasmid-mediated resistance genes that produce a proteins that can bind to the target DNA gyrase and protect it from drug.
- • Mutation in the DNA gyrase that can decrease its binding affinity to quinolones, reducing drugs effectiveness
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