Chapter 7: The Control of Microbial Growth Flashcards
Sterilization
Desruction or removal of all forms of microbial life, including endospores but with the possible exception of prions
Usually done by steam under pressure or sterilizing gas, such as ethylene oxide
Commercial Sterilization
Sufficient heat treatment to kill endospores of Clostridium botulinum in canned food
More-resistant endospores of thermophilic bacteria may survive, but they will not germinate and grow under normal storage conditions
Disinfections
Destruction of vegetative pathogens
May make use of physical or chemical methods
Antisepsis
Destruction of vegetative pathogens on living tissue
Treatment is almost always by chemical antimicrobials
Degerming
Removal of microbes from a limited area, such as the skin around an injection site
Mostly a mechanical removal by an alcohol-soaked swab
Sanitation
Treatment intended to lower microbial counts on eating and drinking utensils to safe public health levels
May be done with high temperature washing or dipping into a chemical disinfectant
Germicide
Rapidly kills M/O, but not necessarily endospores
Fungicide
Kills fungi
Virucide
“Kills” or inactivate viruses
Bacteriostasis
“Stasis” = Halt
Ihibits bacterial growth and multiplication
Sepsis
Greek word for decay/putrid.
Indicator of bacterial contamination
Asepsis
The absence of pathogens from an object or area
Critical in surgical procedures!
Microbial Death Rate
Populations of m/o subjected to a treatment die a constant rate
This “death rate” can be plotted as a straight line
Conditions Influencing Microbial Death
Types and numbers of microbes
Temperature
Physiological state of the m/o
Environment
Time of exposure
Where Do Antimicrobial Agents Work?
The plasma membrane:
Cell membrane permeability may be
affected by altering lipid and protein
content -> “Leaky” membranes
Where Do Antimicrobial Agents Work?
Nucleic acids (DNA and RNA) and proteins: Some antimicrobials break bonds that hold these molecules together, others interfere with synthesis
Physical Methods of Microbial Control?
Heat (moist vs. dry) Filtration Temperature Dessication Osmotic Pressure Radiation (ionizing vs. non-ionizing)
Physical Methods of Microbial Control - Heat
A. Dry heat: Incineration, hot air sterilizationrequires 170°C for 2 hours
B. Moist heat: Boiling (10 min) kills most m/o; but spores and viruses may survive
Autoclaving = Steam under pressure, moisture must touch every surface to sterilize
15 psi, 121°C, 15 min
C. Pasteurization: Mild heating that is sufficient to kill spoilage or disease organisms without damaging the taste of the product (72°C, 15s)
HTST vs. UHT
Physical Methods of Microbial Control - Filtration
Used for heat-sensitive liquids passed
through a membrane filter with pores too small for
m/o to pass through (0.22μm, 0.45μm)
HEPA (High efficiency particulate air) filters = 0.33μm
Physical Methods of Microbial Control - Low Temperatures (depends on the bacteria) At refrigerator temperatures (4°C))
Metabolic rates of most m/o are reduced
Bacteriostatic
Most m/o are dormant in the freezer (-20°C)
Physical Methods of Microbial Control - Dessication (removal of water)
Water is required for growth; dried foods won’t support m/o growth
But, restoring water restores growth
Lyophilization (freeze drying) involves fast
freezing (-70°C) and removal of water in a vacuum
Physical Methods of Microbial Control - Osmotic Pressure (high salt or sugar concentration)
Hypertonic environment
Generally, molds and yeasts resist osmotic pressure
better than bacteria
Physical Methods of Microbial Control - Radiation
A. Ionizing radiation: X-rays, gamma rays
Short wavelength
“Unzip” the strands of DNA
Used to sterilize pharmaceuticals, disposables, and mail…
B. Non-ionizing radiation: UV light
Less energy, less penetrating than ionizing
Causes DNA damage (mutagenesis), thymine dimers
“Germicidal” lamps
C. Microwaves kill indirectly by heating food, but…
The Problem
No single disinfectant is an “all purpose” agent.
It is essential to find the proper agent/purpose!
