Control of Microbes

chapter 11

physical methods of microbial control

Heat, radiation, filtration

Moist Heat vs Dry Heat

moist heat is generally more effective than dry heat

Autoclave

moist heat method

121-132 degrees c

very effective, takes 10-40 min

pressurized steam

used in med, lab, and indust settings for instruments

Pasteurization

moist heat method

63-72 degrees c

reduces microbial growth

inactivates most viruses and vegetative cells

usually used for foods (does not affect consistency)

Baking

dry heat method

150-180 degrees c

takes longer than moist heat (2-4 hr)

Incineration

dry heat method

microbes burn to ash

examples: bunsen burners, furnaces, incinerator

non-ionizing radiation

radiation method

UV light

forms thymine dimers (abnormal DNA connection)

good for surfaces

ionizing radiation

radiation method

gamma rays+ x rays

damage DNA and proteins

sterilize heat-sensitive materials (used for packaging)

filtration

filtration method (physical)

pass air or liquid through membrane filters

pore size determines what gets through

can be sterilizing

good for heat-sensitive materials

chemical methods of microbial control

Phenols and Phenolics
Alcohols

Chlorine and Iodine (halogens)
Oxidizing Agents
Surfactants

factors affecting chemical control

nature of treated material

degree of contamination

exposure time (to the chemical)

strength and chemical action of the agent

levels of chemical agents

high- will kill endospores, may sterilize

intermediate- will kill fungal spores, viruses, and vegetative cells

low- kills only vegetative bacterial, and fungal cells and some viruses

Phenols and Phenolics

effective against vegetative bacteria, fungi ,and most viruses

disrupts cell membranes and denatures proteins

Phenols vs Phenolics

phenol is a good disinfectant (nonliving), phenolics are a good antiseptic (living)

Alcohols

chemical method

effective against vegetative bacteria, fungi, and envelope viruses

disrupts cell membranes and denatures proteins

how? 70% OH 30% H2O

antiseptic and disinfectant (living and non living)

Chlorine

halogen chemical method

effective against bacteria, fungi, and viruses. potentially endospores

forms disulfide bridges and denatures proteins

negative effect by sunlight and organic matter

Iodine

halogen chemical method

effective against bacteria, fungi, and viruses

denatures proteins by forming hydrogen bonds and disulfide bonds

disinfects liquid (water)

Hydrogen peroxide

oxidizing agent/ chemical method

effective against vegetative bacteria, fungi, viruses, potentially endospores (high concentration)

denatures by oxidation (loss of electrons)

disinfectant and antiseptic (non living+living)

surfactant

chemical method

example: soaps and detergents (amphipathic)

disrupts membranes by being both hydrophobic and hydrophilic

bacteria sometimes gains resistance

ethylene oxide

very strong

used in space