Sterilization - removal/destruction of all living microbes and spores and viruses

Disinfection - Killing of vegetative pathogens on a surface (inanimate objects); usually w/ chemicals

Antisepsis - reduction of pathogens from living tissues (sepsis/asepsis)

Degerming - removal of transient microbes from skin by mechanical cleansing or by an antiseptic

Sanitation - related to hygienic practices; reduction in overall total microbial numbers to safe levels

Exposure to antimicrobials can reduce cell numbers at a negative logarithmic rate.

Total cell count - how many total cells there are

Viable cell count - the cell count of the sample taken that are alive

• Bacteriostatic - growth inhibitory; no killing of cells. The addition of a treatment prevents growth, not killing them

• Bacteriocidal - killing of cells. Only viable cell count decreases because the cell is still there

• Bacteriolytic - killing of cells but also cause cells to lyse (break apart). Both total and viable cell count decrease because the cell is destroyed

D-Value - has to do with the logs of death. time for an agent to kill 90% (one log) of the population.

Efficacy of antimicrobial agent → decimal reduction time or D-value

One log is equal to 90% of a population

Factors influencing efficacy of antimicrobial treatments:

• umber/types of microbes present

• organic load or cleanliness

• Exposure time/dose

• pH, temperature

Ways to test efficacy of antimicrobial agents:

• Use-dilution test

  • Metals rings are dipped in test bacteria and then dried → The dried rings/culture are placed in disinfectant for a time at a specific temp (10 min @ 20ºC) → Rings are transferred to culture media to determine whether bacteria survived treatment (incubate 24 hr, check for growth)

• Disk Diffusion Method

  • Filter disks soaked in chemical agent are placed on plate inoculated w/ bacteria. Analyze zones of inhibition → proportional to effectiveness of disinfection

  • is the area under and around the filter disks growing bacteria or not?

Actions of Microbial Control Agents

Agents can target one or a combination of these three parts:

• Plasma membrane - dissolve the plasma membrane

• proteins - denaturing or break down of protein to reduce or eliminate the functionality

• nucleic acids - break down, denature, or chemical alteration

Physical Agents of Control

Temperature

• High temp & pressure

  • Boiling: 10 min @ 100ºC

  • Steam under pressure

  • Autoclave: 15 psi/121ºC/15 min

    • Sterilization method, kills endospores

• Dry Heat Sterilization

  • Incineration; hot air

  • Equivalent to Autoclave in which it sterilizes

  • 170ºC, 2 hr

• Pasteurization - mild heat; for food/beverages

  • NOT a sterilization method; all about preserving the form, color, etc of the product

  • low temp, long time (63º/30 minutes)

  • High temp, short time (72º/15 seconds); flash pasteurization

  • Ultra high temp (134ºC/1-2 seconds)

  • Milk Pasteurization targets Coxiella burnetii

Cold temperature:

• slows down growth

• food & cell preservation (refrigerate or freeze, -20ºC, -80ºC)

• For microbial preservation

• Listeria spp - grows at refrigeration temperature

Filtration - aqueous solutions & air

• Membrane filtration: for heat-labile liquids; .45 um, .2 um pore sizes

• HEPA (air) removes microbes >.3 um

High pressure, Desiccation, Osmotic pressure

Irradiation - used to sterilize food & non-biologicals

• Wavelength of the light

• short wavelength have high energy and long wavelengths have low energy

• Non Ionizing radiation (UV)

  • wavelength - 200-300 nm

  • creates mutation

  • does not penetrate well

  • best for surface disinfection

• Ionizing radiation (X rays, gamma rays, electron beams)

  • wavelength <.1 nm

  • ionizes water to release OH

  • can break and fragments of nucleic acids

  • penetrating radiation

Chemical methods of Control

Phenolics - disrupts lipids of plasma membrane & denature proteins

• Remain active on surface after application

Halogens - alter proteins synthesis & membranes

• Iodine

• Chlorine (bleach); oxidizing agents

Alcohols - require water; denature proteins, dissolve lipids

• Ethanol, isopropanol

• Pure Ethanol actually isn’t as effective as Ethanol mixed with water because the water helps with the killing effect

Heavy metals - Ag, Hg, and Cu; denature proteins

• can be toxic: use at low concentrations

Surface-Active Agents, Surfactants - mimic phospholipid structure and disrupt membrane integrity

• mimic phospholipid structure which helps disrupts the plasma membrane of cells

Chemical Preservatives - control molds/bacteria in foods/ cosmetics

• Organic acids: alter internal pH; inhibit metabolism

  • Sorbic acid, benzoic acid

Gaseous Sterilants - denature, modify proteins

• For heat-sensitive materials → plastics

• Ethylene Oxide

Resistance to disinfectants is based on concentration

• At proper concentration, disinfectants can have multiple targets → makes it difficult to gain a resistance bc difficult to evolve multiple mutations to counteract all effects

• Resistance is more likely at lower concentration of disinfectants since they are more likely to only affect single targets, which allows these bacteria to become resistant to them