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• Control of microbes in healthcare facilities, laboratories, and home is critical in microbiology
• Disease prevention economically saves on morbidity and mortality more than disease treatment

Basic Principles of Microbial Control

• Using correct microbiology terminology prevents miscommunication by scientists and healthcare workers

Sterilization

• Completely removes and destroys all microbes, including viruses and bacterial endospores, but not prions

Aseptic

• An environment or procedure that is free of pathogens
• Surgeons use aseptic techniques in operating rooms to prevent spreading microbes to patients

Disinfection

• Destroys microorganisms by physical or chemical agents, like bleach, UV light, etc.
• Does not kill all pathogens like sterilization, cannot kill endospores or certain viruses
• Only refers to the treatment of inanimate objects
• Antisepsis is when a chemical is safe to use on skin/biological tissue
• The chemical is called an antiseptic

Degerming

• Removes microbes from a surface via scrubbing
• Refers to the act of scrubbing with a chemical agent

Sanitization

• Disinfecting places and utensils used by the public to reduce pathogenic microbes to meet health standards

Pasteurization

• Heating food or beverage just enough to reduce the number of microorganisms without reducing quality

• Reduces the amount of microbes to prevent illness, but doesn't eliminate them all

• Sterilization and disinfection are the primary means of controlling pathogen populations

• Aseptic techniques are forms of sterilization

• Degerming, sanitization, and pasteurization are types of disinfection

• "-static" means the agent inhibits microbial metabolism and growth

  • But DOESN'T kill microbes, e.g. bacteriostatic, virostatic, fungistatic, germistatic

• "-cide/cidal" means the agent destroys or permanently inactivates a microbe

  • E.g. bactericide, virocide, fungicide, germicide

Microbial Death

• Microbial death is a permanent end to reproduction under ideal environmental conditions
• Microbial death rate is calculated to determine how effective an antimicrobial agent is, it is constant over time
• Microbicidal agents kill a constant percentage of cells over time, but not at the same time intervals

Action of Antimicrobial Agents

• Antimicrobial agents can be split into 2 categories:
  • Agents Which Interrupt Cell Walls or Cell Membranes
    • Cell walls control structural integrity and protect from osmosis, cells die if destroyed
    • Cell membranes keep cytoplasm with needed proteins and cellular material
    • Without cytoplasmic membranes cells cannot survive
  • Agents Which Interrupt Cell Metabolism
    • Proteins regulate the cell as enzymes for structure, proteins become denatured by chemical/physical agents
    • Denaturation makes proteins or acids lose some structure
      • No longer participate in metabolic or structural processes
    • Nucleic acids affected by denaturation as components of cells
    • Ribosomes are proteins with nucleic acid portions, destruction leads to the end of protein synthesis

Selection of Microbial Control Methods

• Factors must be considered when using an antimicrobial agent
  • Site to be treated
    • Take care not to cause harm to the place you're treating
    • Harsh chemicals aren't good on the human body or parts
    • Medical instruments need sterilization
  • Susceptibility of Microorganism
    • Choose an effective agent to eliminate the toughest microbe present
    • Eliminating the most resistant organisms is key here!
    • Microorganism Resistant Ranking:
      • Most Resistant:
        • Prions
        • Bacterial endospores
        • Mycobacteria
        • Cysts of protozoa
        • Active-stage protozoa (trophozoites)
        • Most Gram-negative bacteria
        • Fungi
        • Nonenveloped viruses
        • Most Gram-positive bacteria
        • Enveloped viruses
      • Most Susceptible
  • Germicide Effectiveness
    • High-Level: Sterilizes all pathogens and endospores
      • Pacemakers, catheters, central lines, endotracheal tubes
    • Intermediate-Level: Kills up to protozoan cysts
      • Disinfects noninvasive medical instruments like respiratory masks, endoscopes, etc.
    • Low-Level: Eliminates vegetative bacteria, fungi, and some viruses
      • Disinfects items only contacting skin like furniture, electrodes and stethoscopes
  • Environmental conditions
    • Temperature and pH affect the efficacy of antimicrobial methods
    • Warm disinfectants and acidic conditions provide stronger antimicrobial effect

Physical methods of control

• Heat related
  • High temperature denatures proteins, interferes with membrane + wall integrity
  • Moist heat and dry heat

Moist Heat

• Disinfects, sanitizes, sterilizes, and pasteurizes
  • Better conductor of heat than dry heat because of water
  • Boiling
    • Kills vegetative cells of bacteria, fungi, protozoa, and some viruses in 10 minutes
    • Doesn't kill endospores, some viruses, or cysts which isn't sterilization
  • Autoclaving
    • True sterilization because boiling temperature is not hot enough
    • To achieve higher temperature, pressure must be added
    • Pressure tubes and connecting pipes inject water and air
    • 121C and 15 PSI destroys all microbes in 10 minutes
  • Pasteurization
    • Heating a food or beverage product just to control pathogenic population without damaging the product
    • Not sterilization

Dry Heat

• Used for substances that can’t be exposed to water, like powders, oils, and rustable objects
• Requires higher temperatures and longer times to sterilize
  • Oven must be run at 171C for 1 hour with respect to 121C in autoclave for < 15 minutes
• Incineration removes all microbial organisms
  • Heating loops until red (1500C), incinerating carcasses

Cold Related

• Halts metabolism and organism growth
  • Refrigeration at 0C and 7C (32F - 44F)
    • Except psychrophiles, Listeria, and Yersinia
      • Listeria grows in refrigerated foods causing food borne illness
      • Yersinia multiplies in refrigerated blood and transmits through transfusions (bubonic plague)
  • Freezing Below 0C
    • Slow freezing is much better because ice crystals puncture plasma membranes
    • Many bacteria and viruses survive, so cold techniques don’t sterilize

Dessication & Lyophilization

• Dessication removes the amount of water
  • Inhibits microbial growth because metabolism requires water, dried food serves as preservation
• Lyophilization combines drying with freezing

Filtration

• Passage of liquid or gases through filters to trap organisms
  • Bacteria be stored without ice crystals
  • Vacuum cleaner with HEPA filter

Osmotic Pressure

• High concentrations of sugars and salt stops growth via osmotic pressure
• Osmosis moves water to lower water concentrations using salt or sugar
  • Draws water from the cell to inhibit growth in beef jerky, jelly, honey
  • Fungi are more resistant to osmotic forces than bacteria

Radiation

• Particulate forms use subatomic particles freed of atoms
• Electromagnetic forms energy released from an atom
  • Short wavelengths are more powerful and penetrating
  • Ionic Radiation
    • EM waves with wavelengths<1nm
    • Enough energy to dislodge electron, oxidation, and hydroxyl atoms
  • Nonionic Radiation
    • EM waves >1nm
    • UV light inhibits transcription and replication

Chemical Methods of Microbial Control

• Phenolics
  • Carboxilic acid/Phenol is a mild acid
  • Phenolic compounds like halogens/organic groups better antimicrobial properties
  • E.g. Chlorinated Phenols have chlorine with increased antimicrobial action
  • Bisphenolic compounds are antimicrobial agents inside Lysol
  • Act by denaturing protein
  • British surgeon Joseph Lister used this for antiseptic technique with Phenol on incisions

Alcohols

• Intermediate disinfectants that act by denaturing proteins and disrupting cell membranes
  • Needs water (pure ineffective)
  • Does NOT kill bacterial endospores or fungal spores
  • Isopropanol, wood/methanol, and ethanol are examples

Halogen

• Reactive, nonmetallic, and electron short leading to denaturing proteins and enzymes with halogens
  • Pool sanitizer like Chlorine, antiseptic Iodine, and toothpaste Fluorine
  • Fluorine prevents tooth decay

Oxidizing Agents

• High level disinfectants/antiseptics with oxidative metabolism prevention, effective killing of anaerobes in deep wounds
  • Hydrogen peroxide, ozone, paracetic acid

Surfactants

• "surface active" chemicals lower solvent surface tension to dissolve solute molecules
  • Low level like detergents for soaps

Heavy Metals

• Possess toxic properties with high atomic weights
  • Combine with sulfur atoms in cysteine and denature proteins
  • Copper interferes with algae, silver nitrate treats newborns

Aldehydes

• Molecules with terminal CHO with a double bond - Denature proteins by crosslinking disrupting functional microbial groups

Gaseous Agents

• Used for components that cannot be sterilized easily and gas the items • These gasses penetrate paper and plastic wraps and penetrate every crack of an object

Enzymes

• Enzymes like lysosomes (tears that target bacterial cell walls) and Prionozyme (target prions on surgical equipment) kill cells through various processes - Approved in Europe