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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)
- Chemostat / Bioreactor
- can grow infinitely
Introduction of microbes into medium
Measuring Microbial Growth
- Direct Measurements: Microscopically total count; dilute + plate + colony count
- Indirect Measurements: turbidity; Metabolic activity
- Total Counts
- Viable Counts
Actions of Microbial Control Agents
- • Alternation of membrane permeability
- • Damage to proteins
- • Damage to nucleic acids
Removal of all microbial life, including endospores
- Moist heat/Steam sterilization
- Kills vegetative cells and spores.
- Good for utensils and liquids.
- Might affect heat sensitive biological compounds
- • 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
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.
done to loops and straight-wires in microbiology labs.
- 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.
- • 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).
- • Radiation damages DNA
- • Ionizing radiation (X rays, gamma rays)
- • Nonionizing radiation (UV)
- • Microwaves kill by heat; not very antimicrobial
- Causes modification of DNA by cross-linking DNA.
- Used to decontaminate surfaces and materials that do not absorb light, such as air and water.
- -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
Low temperatures and freezing inhibit growth, but
does not kill microorganisms.
Removal of all microbial life.
Lower microbial counts.
substances that are applied to nonliving objects to remove pathogens.
substances that are applied to living surfaces such as skin to to remove pathogens.
Substance produced by one microorganism that can destroy or inhibit the growth of other microorganisms.
a compound or substance that kills or slows down the growth of bacteria.
Substance that can kill bacteria.
Capable of inhibiting the growth of a bacteria. some bactericidal sub becomes bacteriostatic at low concentration.
- antiseptic surgery
- promoted the idea of sterile surgery.
- Used carbolic acid (phenol) to sterilize surgical instruments and to clean wounds
Chemical Antiseptics and Disinfectants
- Alkylating agents: Ethylene oxide, aldehyde
- Heavy metals
- Phenols and derivatives
- Used as gas vapor.
- sterilize heat sensitive equipment and drugs.
- Efficient but limited use: Flammable, explosive and carcinogenic.
- • Inactivate proteins by cross-linking with functional groups (–NH2, –OH, –COOH, —SH).
- • Glutaraldehyde and formaldehyde.
- Denature proteins and enzymes by binding to reactive groups resulting in their precipitation and inactivation.
- Mercury containing compound used as antiseptic.
- 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
- Iodine: Povidone iodine. To clean skin before surgery with soap -> alcohol -> iodine (red).
- Chlorine: Used in swimming pools, water treatment units, and bleach.
Phenols and derivatives (Phenolics)
- Phenol: mouth rinses (Listerine), Lysol
- Triclosan: anti-bacterial soap
- Disrupt plasma membranes
- Hydrogen peroxide (H2O2)
- Kills bacteria at 3-6%.
- Kills spores at 10-25%.
Detergents - Surface-Active Agents or Surfactants
- Dissolve membranes.
- SDS: Most common ingredient in toothpaste.
- Chlorhexidine: in mouth rinses.
Antimicrobial Agents Selective toxicity
a drug that kills bacteria without damaging the host: Therapeutic index
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.
Growth Factor Analogs
- synthetic metabolic inhibitors
- sulfa drugs, isoniazid, and nucleic acid analogs
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
Nucleic acid analogs
- Blocks nucleic acid synthesis.
- Used to treat viral and fungal infections.
Quinolones and Fluoroquinolones (Ciprofloxacin)
- Blocks and inhibits DNA gyrase (unwinds DNA) - DNA replication is stopped.
- Used to treat urinary tract infections, penicillin resistant anthrax, and TB.
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