BIO3 - Chapter 7

The control of Microbial Growth

sepsis

microbial contamination

asepsis

absence of significant contamination

what do aseptic surgery techniques prevent

microbial contamination of wounds

sterilization

removing all microbial life

commercial sterilization

killing clostridium botulinum endospores

disinfection

removing pathogens

antisepsis

removing pathogens from living tissue

degerming

removing microbes from a limited area

sanitization

lowering microbial counts on eating utensilis

biocide/germicide

kills microbes

bacteriostasis

inhibiting microbes

death rate of population

90%, constant

factors that determine effectiveness of treatment

# of microbes, environment, time of exposure, microbial charcteristics

actions of microbial control agents

alteration of membrane premeability, damage to proteins damage to nucleic acids

physical methods of microbial control

heat, filtration, low temperature, high pressure, desiccation, osmotic pressure, radiation

thermal death point (tdp)

lowest temp at which all cells in a culture are killed in 10 mins

thermal death time (tdt)

time during which all cells in a culture are killed

decimal reduction time (drt)

time to kill 90% of cells at a given temperature

moist heat sterilization

denatures proteins; boiling, steaming, autoclaving, pasteurization

autoclave

steam under pressure; 121C at 15 psi for 15 mins; kills all organsims & endospores

pasteurization

reduces spoilage organisms & pathogens; high-temp short time & ultra-high-temp (<1 sec)

ways to dry heat sterilize

incineration, flaming; hot-air sterilization

filtration

used to sterilize heat-sensitive materials

low temperature

inhibits microbial growth (bacteriostatic effect)

low temperature techniques

refrigeration, deep-freezing, lyophilization (freeze-dry)

high pressure

denatures proteins

desiccation

lowers metabolic rate

osmotic pressure

causes plasmolysis

radiation

change DNA

radiation examples

x-ray, gamma ray, uv, microwaves

ionizing radiation

ionizes H2O to create reactive hydroxyl radicals; damages dna by causing mutations

ionizing radiation examples

x-rays, gamma rays, electron beams

nonionizing radiation

damages dna by creating thymine dimers

nonionizing radiation example

ultraviolet

microwaves

kill by heat; not especially antimicrobial

principles of effective disinfection

concentration of disinfectant, organic matter, pH, time

use-dilution tests

metal dipped in bacteria & dried, placed in disinfectatn, transferred to culture media to see if bacteria survived treatment

disk-diffusion method

see how efficient chemical agents are, look for zone of inhibition around disk

phenol & phenolics

discupt plasma membranes, causing leakage

phenol

rarely used

phenolics

used on environmental surfaces

bisphenol

hexachlorophene & triclosan; disrupt plasma membranes; soaps & skin lotions

alcohols

ethanol & isopronal; denature proteins, dissolve lipids, req H2O

tinctures

iodines in aqueous alcohol

iodophors

in organic molecules, release iodine gradually

iodine

alter protein synthesis & membranes

chlorine

bleach: hypochlorous acid; chloring gas, oxidizing agents; shut down cellular enzyme systems

heavy metals

denaturation of enzymes & other protein

heavy metal examples

silver, mercury, copper

sulfadizaine tropical cream

copper sulfate - algicide

peroxygens

oxidizing agents; used on contaminated surfaces (hydrogen peroxide & ozone)

gaseous sterilants

denature proteins, damage dna; use on heat-sensitive material (ethylene oxide)

aldehydes

inactivate proteins by cross linking with functional groups; used on medical equipment

chemical food preservatives

sulfure dioxide, organic acids, nitrite, antibiotics

sulfure dioxide

prevents wine spoilage

organic acids

inhibit metabolism, control molds & bacteria in foods & cosmetics

organic acids examples

sorbic acid, benzoic acid & calcium propionate

nitrite

prevents endospore germination; used in processed meats

antibiotics

nisin & natamycin; prevent spoilage of cheese

most resistant to least resistant microbes

prions, endospores, mycobacteria, protozoa, gram-neg bacteria, fungi, viruses without envelope, gram-pos bacteria, viruses with envelope

agents that injure plasma membrane

phonol/phenolics

bisphenols

chemical agents that damage proteins

iodine + chlorine

alchohols

heavy metals

aldehydes

gaseous sterilants (Ethylene oxide)

chemical agent that damage dna

gaseous sterilants (Ethylene oxide)

chemical methods of microbial control

phenols & phenolics

bisphenols

iodine & chlorine

alcohol

heavy metals

aldehydes

gaseous sterilants

peroxygens

ideal ethanol %

60%-95%

bactericidal v bacteriostatic tests

initial test: (-) bactericidal & bacteriostatic

subculture: (-) bactericidal; (+) bacteriostatic