Physical growth control

methods used by civilizations to control microbial growth

Salting, smoking, pickling, drying, and exposure of food and clothing to sunlight

Purpose of spices in early cooking

Mask taste of spoiled food, some spices prevented spoilage

Who helped develop aseptic techniques in the mid 1800s

Semmelweiss and Lister

Purpose of aseptic techniques

Prevent contamination of surgical wounds

Death rate from nosocomial infections before aseptic techniques

10% of surgeries

Mortality rate of mothers delivering in hospitals before aseptic techniques

Up to 25%

Killing or removing all forms of microbial life (including endospores) in a material or an object

Sterilization

Most commonly used method of sterilization

Heating

Heat treatment that kills endospores of Clostridium botulinum in canned food

commercial sterilization

Endospores not killed in commercial sterilization

Endospores of thermophiles

Growth temperature of thermophiles

Above 45C

Reducing the number of pathogenic microorganisms to the point where they no longer cause diseases

disinfection

Microbial forms usually removed by disinfection

Vegetative or non-endospore forming pathogens

Methods used in disinfection

Physical or chemical methods

Applied to inanimate objects

disinfectant

Antiseptic is applied to

living tissues

Mechanical removal of most microbes in a limited area

degerming

Example of degerming

Alcohol swab on skin

Use of chemical agent on food-handling equipment to meet public health standards

sanitization

Example of sanitization

Hot soap and water

Indicates bacterial contamination

sepsis

Absence of significant contamination

asepsis

Prevent contamination of surgical instruments, medical personnel, and the patient

aseptic techniques

Use of aseptic techniques in industry

Prevent bacterial contamination in food industry

Inhibits the growth of bacteria but does not necessarily kill them

bacteriostatic agent

Meaning of suffix stasis

To stop or steady

An agent that kills certain microorganisms

germicide

An agent that kills bacteria

bactericide

Limitation of most bactericides

Most do not kill endospores

An agent that inactivates viruses

viricide

An agent that kills fungi

fungicide

An agent that kills bacterial endospores and fungal spores

sporicide

Pattern of microbial death during treatment

Die at a constant rate

Effect of number of microbes on treatment effectiveness

More microbes require more time to eliminate

Most resistant microbial form

Endospores

Environmental factors that reduce antimicrobial effectiveness

Organic material, pH

Effect of exposure time on antimicrobial treatments

Longer exposure increases effectiveness

Heat treatment compensation

Longer exposure compensates for lower temperatures

How heat kills microorganisms

Denaturing enzymes and proteins

Lowest temperature at which all microbes are killed in ten minutes

thermal death point (TDP)

Minimal length of time in which all bacteria are killed at a given temperature

thermal death time (TDT)

Time in minutes required to kill 90% of bacteria

decimal reduction time (DRT)

Industry using DRT

Canning industry

How moist heat kills microorganisms

Coagulating proteins

Effectiveness comparison of moist vs dry heat

Moist heat is much more effective

Temperature of boiling

100C or more at sea level

Microbes killed by boiling

Vegetative bacterial pathogens, almost all viruses, fungi and spores

Microbes resistant to brief boiling

Endospores and some viruses

Survival of hepatitis virus during boiling

Up to 30 minutes

Survival of endospores during boiling

Up to 20 hours or more

Requirement for reliable moist heat sterilization

Temperatures above boiling water

Chamber filled with hot steam under pressure

autoclave

Preferred sterilization method

Autoclave

Steam temperature in autoclave

121C

Pressure condition of autoclave

Twice atmospheric pressure

Time required to kill all organisms in autoclave

15 minutes

Autoclave limitation

Require more time for large volumes or solids

Purpose of pasteurization

Prevent spoilage of beverages

Developer of pasteurization

Louis Pasteur

Classic pasteurization method

65C for 30 minutes

HTST pasteurization

72C for 15 seconds

UHT pasteurization

140C for 3 seconds

Advantage of UHT milk

Stored at room temperature for several months

How dry heat kills microorganisms

Oxidation effects

Purpose of direct flaming

Sterilize inoculating loops and needles

Indicator of proper flaming

Metal glows red

Purpose of incineration

Sterilize disposable items and biological waste

Hot air sterilization requirement

2 hours at 170oC

Reason dry heat is less effective than moist heat

Transfers heat less effectively

Removal of microbes by passage through small pores

filtration

Materials sterilized by filtration

Vaccines, enzymes, antibiotics, some culture media

Use of HEPA filters

Remove bacteria from air

Locations using HEPA filters

Operating rooms and burn units

Pore size to remove most bacteria

0.22 and 0.45 um

Microbes not retained by 0.22–0.45 um filters

Spirochetes, mycoplasmas, viruses

Pore size that retains all viruses

0.01 um

Temperature range of refrigeration

0 to 7C

Effect of refrigeration

Bacteriostatic

Effect of freezing

Reduces microbial survival

Does not kill most microbes

flash freezing

Effect of slow freezing

More harmful due to ice crystals

Survival of vegetative bacteria after freezing

Over a third may survive one year

Effect of freezing on parasites

Killed by a few days of freezing

Absence of water prevents growth

dessication

Microbe survival in dessication

Some remain viable for years

Survival of Neisseria gonorrhea in dessication

About one hour

Survival of Mycobacterium tuberculosis in dessication

Several months

Resistance of viruses to dessication

Fairly resistant

Survival of Clostridium and Bacillus spp.

May survive decades

Effect of osmotic pressure on microbes

Creates hypertonic environment

Plasma membrane shrinks away from cell wall

plasmolysis

Effect of plasmolysis on cells

Usually stops growing

Microbes resistant to high osmotic pressure

Yeasts and molds

Bacteria resistant to osmotic pressure

Staphylococci spp.

Ionizing radiation wavelength

Less than 1 nanometer

Effect of ionizing radiation on atoms

Dislodge electrons and form ions

Effect of ionizing radiation on DNA

Cause mutations and produce peroxides

Uses of ionizing radiation

Sterilize pharmaceuticals and disposable medical supplies

Disadvantage of ionizing radiation

Penetrates human tissues and may cause genetic mutations

UV radiation wavelength

Longer than 1 nanometer