Control of Microbe Growth

Controlling Microorganism

• Salting

• Pickling

• Smoking

• Drying

• Sunlight

• Burning

• Water in Copper and Silver Containers

Terminology

Sterilization → Killing of ALL Microbes + Endospores in or on Objects

• Surgical Equipment

• Can’t Sterilize LIVING Humans

Disinfection → Destroy Most Microbes, NOT Endospores → Reduce Contamination

• Disinfectants → Applied to Objects, Toxic to People

Antisepsis (Degermation) → Same as Disinfection but Antisepsis Topically to LIVING Tissues

Decontamination or Sanitization → Cleaning Technique to Remove Most Microbes

• Washing Hands

• Washing Cutlery

Microbial Control Agents - Microbicidal and Microbiostatic

Germicide and Microbicide → Agents that Kill Microbes

Static → Inactivate, not Kill Microbes

Bactericide → Kill Bacteria

Bacteriostatic → Inhibit Bacteria Growth

Viricide → Inactivate Virus

Fungicide + Fungistatic → Kill or Inhibit Fungi

Sporicide → Destroy Endospore

• Sterilizing Treatment

Factors that Impact Treatment

Nature of Organism

Degree / Number of Microbes

Time of Exposure

Strength of Agent

Microbial Control on Medical Devices

Critical Medical Devices

• Contact with Sterile Tissue (Surgery)

Semi-critical Medical Devices

• Contact with Mucosal Membranes (Not Surgery) (Tongue Depressor)

Non-critical Medical Devices

• Contact with Skin

Concerns in Control

Sterilization?

Reuse or Discard?

Withstand Heat, Pressure, Radiation, Chemicals?

Agent Effective?

Cost Efficient and Safe?

Selecting Microbicide

• Action even in Low Concentration

• Soluble in Water or Alcohol + Stable Long Term

• Broad Action without Toxicity

• Penetrate Surfaces

• Resistance to Being Inactivated

• Non-Corrosive/Stain

• Sanitizing and Deodorizing

• Affordable

Targets of Most Germicides

• Proteins

• Cell Wall

• Cell Membrane

• Nucleic Acids

Chemical Antimicrobial Agents

Soaps + Detergent → Surfactant, Amphipathic

• Water Loving + Hating Regions

• Disrupt Cell Membrane

Acids + Alkylating Agents

• Denature Proteins

• Disrupt pH Balance

Heavy Metals

• Silver, Mercury, Coppy

• Denature Inactive Proteins

Halogens

• Chlorine, Iodine

• Oxidize Cell Components

Alcohols

• Denature Proteins

• Disrupt Lipid Bilayer

• Not Good vs Endospores or NON-Enveloped Virus

Phenols (Carbolic Acid)

• Disrupt Protein + Cell Membrane

Oxidizing Agents

• Hydrogen Peroxide

• Denature Proteins

Dyes

• Induce Mutations

• Interfere with Replication and Wall Synthesis

Surfactant

Dissolves Lipids

• Soaps, Detergents, Alcohols
  
  

Amphipathic → Hydro Loving and Hating Regions

• Disrupt Cell Membrane

• Loses Selective Permeability

Remember: Membranes are Made of Lipids

Other Agents Review

Halogens → Chlorine

• Liquid and Gaseous Chlorine

• Don’t Breath

• Hypochlorite → Bleach is a Weak Solution of Sodium Hypochlorite

• Chloramines → Treat Water Supply

• Kill Endospores

• Less Effective Exposed to: Light, Alkaline pH, Excess Organic Matter

Heavy Metal

• Oligodynamic → Toxic in Small Amounts

• Mercury and Silver are Significant Germicides

• Toxic to Humans

• Allergic Reactions

• Neutralized by Body Waste

• Microbe Resistance

Phenols

• Lister Disinfectant in 1867

• Standard to Compete

• Phenol Coefficient

• Lysol has Coeff of 5 against S. Aureus, 3.2 against S. Typhi

• Ethyl Alcohol → 6.3 against Both

• Triclosan

  • In Antimicrobial Soap

  • Block Enzyme in Bacteria → Fatty Acid Biosynthesis

  • Can’t Reduce Disease Spread

  • Ends up in Environment and Disrupt

Physical Antimicrobial Agents

• Heat → Preferred

  • Higher Temp are Microbicidal

  • Lower Temps are Microbiostatic

• Refrigeration / Freezing

• Drying

• Radiation

• Sonic + Ultrasonic Waves

• Filtration

• Osmotic Pressure

Heat

Dry Heat → Denatures Protein

• Oven, Flaming Loop

• Destroy Endospores

• Slower than Moist Heat

Moist Heat → Denatures Proteins

• Boiling Water → Disinfect, does NOT Destroy Endospores

• Autoclave → Sterilization by Steam

  • Increasing Boiling Point and Pent H2O

Pasteurization → Control Microbial Growth in Food

• Moderate - High Heat → Denature without Ruining Food

• Milk - 71°C for 15 Seconds

• Kills Most Pathogens → Not Sterility or Destroy Endospores

Alkalis and Acids - Change pH

Raise pH → Alkaline

Lower pH → Acidic

Denatures Proteins and Metabolism Stops

Acts as Preservative in Food

• Acetic Acid, Lactic Acid

• Stops Fungal Growth

Cold Temperature + Dessication

Slow Growth, Not Sterilize

Refrigeration → Slow Enzyme Reactions

• Stops Spoiling Short Term → 4°C

Freezing → Slow Enzyme Reactions

• Stop Spoiling Longer (-20°C)

Drying → No Water Inhibits Enzymes

Freeze Drying (Lyophilization) → Inhibits Enzymes

• Drying Materials from Frozen State

• Long Term Preservation

Radiation

Ionizing Radiation → Short Wavelength, High Intensity Radiation Energy

• High Pent

• Electrons Ejected from Cell Molecules and Breaks Bonds

• X-Rays, Gamma Rays

UV Light - Long Wavelength, Less Intense

• Poor Pent

• Excites Electrons to Higher Energy State

• Formation of Abnormal Bonds and Breaks

• Mutations

Filtration

Sterilize Materials Damaged by Heat Sterilization

Filter to Separate Microbes from Liquid or Air

Pores Large enough for Liquid / Air but Too Small for Microbes

Mechanically Removes Microbes

Membrane Filters Commonly Used

Osmotic Pressure

Salt or Sugar Creates Hypertonic Environment

Water Escapes Microbes

• Plasmolysis → Loss of Water, Cell Shrink

Interfere with Cell Function

Curing Meat → Pickling