Control of Microbial Growth

Why control microbial growth?

1. prevent transmission of infectious disease

2. aseptic techniques for medicine

3. prevention of spoilage

4. prevention of foodborne illnesses

Sterilization: __________ of all forms of microbial life

Disinfection: control directed at __________. Destruction of vegetative pathogens on inert surface

Antisepsis: destruction of __________

Degerming: _____ removal of most microbes in a limited area

Bacteriostasis: method or agent which __________

Biocide/germicide: method or agent which __________

Removal or destruction; destroying harmful microorganisms; vegetative pathogens on living tissue; mechanical; inhibits microbial growth; kills microbes

The rate of microbial death is _____. The growth of microorganisms can be controlled by physical, chemical, mechanical, and biological means. The effectiveness of treatment depends on:

exponential; number of microbes, environment, time of exposure, and microbial characteristics

Actions of microbial control agents:

Alteration of __________

Damage of _____

Damage of _____

Inhibition or alteration of _____

membrane permeability; proteins; nucleic acids; metabolism

High temperature methods of sterilization:

Dry heat kills by _____

• flaming

• incineration

• hot air sterilization

Moist heat _____ and _____ proteins

• boiling

• autoclaving

• paseurization

oxidation; coagulates; denatures

Advantages of moist heat:

• high __________

• not _____

• low _____ and not __________

Disadvantages of moist heat:

• some items can not _____ the high temperature of steam

• not suitable for __________

penetrating power; toxic; cost; time consuming; withstand; powder or oils

Vegetative bacteria are killed by _____ and require immersion in boiling water at _____ for _____ minutes

boiling; 100ºC; 15

Autoclave is effective in the destruction of __________. Sterilization of culture media, surgical instruments, dressings, gowns, cotton, gauze, etc. Beenfits: __________. Autoclaving requires steam under pressure at _____ at _____ for _____ min. Steam MUST contact the item’s _____

bacteria, viruses, spores, fungi, and other pathogenic organisms; nontoxic, cheap, and rapid; 121ºC; 15 psi; 15; surface

Pasteurization reduces the _____ organisms and pathogens by heating material for a __________. Water and certain packaged and non packaged foods are treated with mild heat. This does not render the food _____ as it can’t destroy _____. Developed by _____ in the 1860s

spoilage; short time; sterilized; endospores; Louis Pasteur

Pasteurization requires mild heat followed by __________. Eliminates _____ and extends shelf life. Equivalent treatments:

• 63ºC for 30 minutes

• High temperature short time (HTST): _____ for _____

• Ultra high temperature (UHT): _____ for _____

rapid cooling; pathogens; 72ºC; 15 seconds; 140ºC; 4 seconds

Filtration is the passage of substance through a screen like material used for _____ materials. High efficiency particulate air (HEPA) filters remove microbes > _____ micrometers in diameter. Membrane filters remove microbes > _____ micrometers

heat sensitive; 0.3; 0.22

Blue light (_____ nm) is used to kill MRSA. Microwaves kill by _____; not especially antimicrobial. Ionizing radiation (x-rays, gamma rays) produce reactive molecules that damage _____. Nonionizing radiation (ultraviolet) has germicidal wavelength of _____ nm. One of the primary lethal effects of UV light is its _____ properties. Pyrimidine dimers are formed when DNA absorbs UV light:

• __________ are most common

• DNA becomes distorted

• Mutations arise

• Replication stops

470; heat; DNA; 260; mutagenic; thymine dimers

UV light is commonly used for _____ because it is chemical free and environmentally friendly

sterilization

Osmotic pressure uses high concentrations of _____ and _____ to create _____ environments. It causes _____

salt; sugar; hypertonic; plasmolysis

Other physical methods of control in food preservation:

• low temperature has a bacteriostatic effect:

  • Refrigeration

  • Deep freezing

  • Freeze drying

• desiccation: removes _____

  • absence of water prevents _____

moisture; metabolism

Chemical methods of microbial control:

Desirable attributes of a chemical agent

• _____ to humans and pets

• effective at _____ concentration

• suitable for _____ applications

Factors affecting degree/efficacy of disinfection

• concentration of disinfectant

• time of _____

• pH, temperature, organic matter

• microbial characteristics

nontoxic; low; broad spectrum; exposure

Phenol and phenol derivatives: Disrupt cell walls and membranes and precipitate _____. Bactericidal, fungicidal, virucidal, not sporicidal

proteins

Alcohols like ethanol and isopropanol denature _____ and dissolves _____. No effect on _____ and __________.

proteins; lipids; endospores; nonenveloped viruses

Quaternary ammonium compounds: the mechanisms of action is detergent has a __________ to aid in _____ removal; can also disrupt the plasma membrane and denature proteins. Doesn’t kill __________

positive charge; mechanical; endospores, mycobacterium, or pseudomonas

Hydrogen peroxide can be weak (_____) to strong (_____). Lower concentrations are used for _____ because it can produce __________ that can damage proteins and DNA

3%; 25%; tissues; highly reactive hydroxyl free radicals