Microbiology Ch. 11 - Control of Microorganisms (Physical and Chemical Methods)

Exam 1

sterilization

treatment of an object to ensure destruction of all living microbes, spores, and viruses

microbicidals

agents that kill microbes, also called germicidals

bactericidals

agents that specifically target and kill bacteria

fungicidals

agents that specifically target and kill fungi

commercial sterilization

the process of killing all pathogens in a product, particularly in the food supply

sanitization

reduces the numbers of pathogens or discourages their growth, but after a time, microbes and potential pathogens will settle and grow

microbiostatics

agents such as disinfectants and antiseptics that inhibit the growth of all microbes

bacteriostatics

agents that discourage the growth of bacterial species

fungistatics

agents that discourage the growth of fungal species

why do agents target the bacterial cell envelope?

phospholipids and cell membrane proteins are often the target because the interruption of the membrane permeability leads to cell death

why do agents target the proteins and DNA?

denaturation of proteins, especially enzymes, inhibits cell function, and disruption of DNA function inhibits cell growth and division

thermal death point

the temperature (and time) at which a species dies

incineration

(dry heat) uses direct flame to kill microbes

in healthcare settings, disposable hospital gowns and dressings, and certain tools can be incinerated

common to incinerate carcasses of diseased cattle

dry heat

requires long periods of exposure to high temperatures

the heat changes microbial proteins and removes water, slowly burning the microbes

moist heat

faster and effective at lower temperatures than dry heat

kills microbes by denaturing their proteins

boiling water may not kill all spores or inactivate all viruses

autoclaving

(moist heat) pressurized steam is used as an autoclave as a more dependable way to sterilize a variety of objects

pressure of 15 psi at 121 °C for 15-30 minutes

pasteurization

(moist heat) reduces bacterial populations in food and drink, which reduces the chances of spoilage and disease

bacterial spores are not affected by pasteurization

holding (batch) method

also called low-temperature long-time pasteurization

kills disease-causing microorganisms while preserving much of the milks flavor and nutritional value

63 °C for 30 minutes

flash pasteurization

also called high-temperature short-time pasteurization

more efficient than the holding method

destroys pathogenic microorganisms and extends shelf life with minimal effect on taste and nutrients

most common

72 °C for 15 seconds

ultra-high-temperature sterilization

also called ultra-pasteurization

destroys virtually all microorganisms and spores

produces a shelf-stable product that can be stored for months without refrigeration until opened

may cause a slight change in flavor

cold temperatures

slow microbial growth

refrigerators reduce food spoilage when kept near 5 °C

psychrophiles prefer cold temperatures and can contaminate food

freezing food below 0 °C inhibits metabolism and growth of microbes and can kill certain cells when ice crystals penetrate them, but many pathogenic bacteria can withstand long periods in freezing temperatures and multiply rapidly when thawed

filtration

as fluid passes through a membrane filter, microorganisms above a certain size threshold are trapped in the pores

air can be filtered using a high-efficiency particulate air filter

ultraviolet light

can be used to control microbial growth

exposure to UV light causes thymine molecules to link together in DNA

errors in protein synthesis and impairment of chromosome replication then occur

ionizing radiation

x-rays and gamma rays force electrons out of microbial molecules

this affects cell metabolism and physiology

lyophilization

also called freeze drying

food is frozen with liquid nitrogen, then subjected to a vacuum pump to draw off water

drying

also called desiccation

removes the water necessary for microbes to live

salting

causes water to diffuse out of organisms by osmosis, causing dehydration and death

great for high-sugar foods

antiseptics

used to destroy pathogens on living tissue

aseptic technique is critical in surgical settings to prevent contamination

disinfectants

used on inanimate objects to reduce or eliminate pathogens

degerming

mechanically removing organisms from an objects surface

useful disinfectant or antiseptic chemical agents should…

be able to kill or slow growth of microbes and be nontoxic to animals and humans

be soluble in water or alcohol and be easy to apply

have relatively long shelf life

be used in a diluted form

act in short time

be non-staining and non-corrosive

be odorless and easy to obtain

be relatively inexpensive

phenol coefficient

indicates disinfecting ability compared to that of phenol under idential conditions

a higher number than one is more effective than phenol, and lower than one is less effective

drawbacks include being performed in a lab instead of real life, and it does not take into account tissue toxicity and temperature variations

use-dilution test

chemical agents of various dilutions are exposed to a test microbe for 10 minutes and placed in growth medium to see which dilutions are clear of growth

in use test

swabs are taken of a test surface before and after cleaning with a chemical agent and growth is checked after incubation

disk diffusion method

examines the effect of different chemical agents against a specific bacterium

plates are checked for zones of inhibition where bacteria have been eliminated

halogens

oxidize proteins

chlorine

keeps bacterial populations low in municipal water supplies and swimming pools

iodine

used to disinfect wounds, water, and restaurant equipment

iodophors, including betadine, release iodine over a long period of time

phenol

inexpensive, caustic, pungent odor

derivatives have greater germicidal activity and lower toxicity than phenol

bisphenols are combinations of two phenol molecules and are commonly used in disinfection and antisepsis

heavy metals

interfere with microbial metabolism

mercury, copper, and silver are reactive with proteins

they disrupt cellular metabolism by inactivating enzymes and denaturing structural proteins, resulting in the death of microbes

alcohol

denatures proteins and disrupts membranes

effective against vegetative cells but not spores

membrane disruption is caused by lipid dissolution

soap

removes microbes by emulsifying and solubilizing particles on the skin

detergents

surfacant that cause cytoplasm leakage from microbial membranes

quaternary ammonium compounds react with cell membranes and destroy some bacteria and viruses

hydrogen peroxide

damages cellular components

catalase in wounded tissue transforms it to oxygen and water

the oxygen is effective against anaerobic bacteria

sterilizing gases

used on heat-sensitive plastics

ethylene oxide is used as a chemical counterpart to heat and pressure based autoclaves

aldehydes

causes cross-linking that inactivates proteins and nucleic acids

ethylene oxide

effective by carcinogenic and explosive gas

chlorine dioxide

nontoxic and noncarcinogenic gas used to decontaminate anthrax-exposed mail in 2001