Lecture 13 - Control of Infectious Disease (Prevention)

Various ways a pathogen can be eliminated from an environment

Sterilization

Everything (even non-pathogens) is completely destroyed/removed

Sterilant

Agent that helps w/ sterilization

Ex: chemical agents, like ethylene oxide (C2H4O) can be used to sterilize medical devices

Disinfection

Killing/inhibiting/removing microorganisms that may cause disease on INANIMATE objects

Usually done via chemical agents

Sanitization

Cleaning/disinfecting inanimate objects deemed safe by public health standards

Example: restaurant utensils

Antisepsis

Controlling microbes on living tissue through chemical agents

Antiseptics kill/inhibit pathogen growth

Less toxic than disinfectants

-cide vs -static

-cide = to kill

• biocide: an agent that can kill living (can control microorganisms)

• Germicide

• Bactericide

• Fungicide

• Viricide

-static: inhibit growth but does not kill

• if removed/diluted → effect is gone

• bacteriostatic

• fungistatic

Exponential microbial death

Population decreases by the same fraction at constant intervals

• ex: at a particular temp

  • 10% of organisms die in 1st min

  • 10% of living organisms die in 2nd min

  • 10% of living after 2nd wmin will die in 3rd mijn

Decimal reduction time (D value)

Time to kill 90% of microorganisms in a sample at a specific time

Types of physical agents for controlling microbes

1. Filtration

   1. Air

   2. Liquid

2. Heat

   1. Moist

   2. Dry

3. Radiation

Air filtration

Type of physical agent to control microorganisms

Examples

• HEPA filters

  • high-efficiency particle air

  • fiberglass

  • removes 99.97 % of particles ≥ 0.3 µm

  • also captures nanoparticles (≤0.1 µm, like viruses)

• N95

  • excludes 95% of particles ≥ 0.3 µm

  • Hospitals/labs

Liquid filtration

Type of physical agent to control microorganisms

• Depth filter

  • Fibrous or granular material

  • Thick layers with lots of twisting channels of small diameter

  • Solution is sucked through & microbial cells ar trapped

• Membrane filters

  • Synthetic materials

  • Varity pore sizes

    • ~0.2µm in diameter

    • Removes most vegetative cells

Moist heat as a physical agent for removing microbes

• Autoclaves

  • Water boiled → Steam

  • Enters chamber & put under pressurew

  • 121 degrees C & 15 lbs of pressure

• Pasteurization

  • Controlled heating at temps well below boiling

  • Does not sterilize

  • Kills most pathogens, reducing spoilage

Dry heat as a physical agent for removing microbes

Less effective than moist

Does not corrode metal instruments

Sterilizes powders & oils

• Bench top incinerators to sterilize innoculating loops

UV Radiation to control microbial growth

Non-iodizing

260-280 nm

Causes pyrimidine dimer which is literal

• Pyrimidine = C & T

Limiting factor: Can’t penetrate well

Used in rooms in cabinets to sterilize air or exposed surfaces

Ionizing raditaion to control microbial growth — How many types?

3 types

• Gamma rays

• Electron beams

• X rays

Penetrates deep

Damages DNA & produces peroxide

Destroys bacterial endospores & vegetative cells

Uses for ionizing radiation ( ask chat)

Medical: antibiotics, hormones, syringes

Foods

Goal of chemical agents

Be efffective against a wide range of microbes w/o being toxic to humans or corrosive to common material

Examples

1. Phenol

2. Soaps & detergent

3. Alcohol

4. Oxidizing agents

Joseph Lister

Sprayed phenol (a type of carbolic acid) into wounds, incisions, etc) & noticed it prevented infections

• Led to antisepsis in healthcare setting

Phenol & phenolic derivatives

Denature proteins and disrupts plasma membrane

Advantages:

• effective in presence of organic material

• remains active on surface for a long time after application

Disadvantages:

• Bad odor & causes skin irritation

Example of phenol-derivative

Triclosan

• Phenol-derived antiseptic

• Binds to enoyl-ACP reductase (bacterial enzyme)

• Inhibits fatty acid synthesis (important for cell membrane synthesis)

Soaps & detergents

Surfactants (amphipathic)

• allows them to break down and lift away dirt, oil, and bacteria from surfaces or skin

Removes microbes, oil

Action of removing microbes increases w/ scrubbing

Alcohols

• Disinfectants (inanimate) & antiseptics (living tissue)

• Bactericidal

• Inactivates viruses

• Dissolves/disrupts PM

• Ex: ethanol/isopropanol (hand sanitizer)

Oxidizing agents

Strip electrons from molecules

Examples

• H2O2 (3% solution) can be used on skin wounds)

• Tincture of iodine

• Sodium hypochlorite (found in household bleach, swimming pools)

• Wastewater treatment (Chlorine/ozone)

What factors affect the effectiveness of antimicrobial agents

1. Population size

2. Cell type

3. High concentrations of antimicrobial agent

4. Longer duration of exposure

How does population size affect the effectiveness of antimicrobial agents

Fewer organisms = less time needed to achieve sterility

Table shows example of 40% death rate/min

How does cell type affect the effectiveness of antimicrobial agents

Vegetative cells are actively growing and more susceptibel to agents

Younger cells are more susceptible than mature

Cells w/ endospores are more resistant

How does concentration of agent & duration of exposure affect the effectiveness of antimicrobial agents

Increased concentration destroys organisms faster (up to a point)

Longer duration of exposure leads to more killed

Phenolic component

Disinfectant screening test to see the effectiveness of a disinfectant

• Potency of a disinfectant is compared to phenol

• Series of identical dilutions to phenol & experimental disinfectant conducted

Methods of phenolic component test

20ºC water bath for 5 mins so all tubes come to same temp

Inoculated w/ 0.5 ml of test bacteria (Salmonella tyohi & staphyloccus aureus

Test after 5, 10, 15 mins of innoculation

• Transfer into broth & incubate for 48 hours

• Find smallest concentration (highest dilution) that kills all organism after 10 mins

  • This dilution is used to calculate phenol coefficient

How to calculate phenol coefficient

Reciprocal of test disinfectant dilution divided by reciprocal for phenol

ex:

• test infectant dilution = 1/250

• phenol dilution = 1/250

• 250/250=1

  • test disinfectant has same effectiveness as phenol

• test disinfectant dilution = 1/450

• phenol dilution = 1/90

  • phenol coefficient: 450/90=5

T/F: higher phenol coefficient means a more effective disinfectant under those conditions

True