Chapter 7: The Control of Microbial Growth

sepsis

refers to bacterial contamination

asepsis

the absence of significant contamination

• aseptic surgery techniques prevent the microbial contamination of wounds

sterilization

removing and destroying ALL microbial life (bacteria, fungi, endospores)

commercial sterilization

killing Clostridium botulinum endospores from canned goods

disinfection

destroying harmful microorganisms (not destroying spores)

• hand sanitizer

antisepsis

destroying harmful microorganisms from living tissue

degerming

the mechanical removal of microbes from a limited area

sanitization

lowering microbial counts on eating utensils to safe levels

biocide (germicide)

treatments that kill microbes

bacteriostasis

inhibiting, not killing microbes (stops bacteria from growing, does not kill them)

cide

death

stasis

lack of growth

function of heat

to denature enzymes

thermal death point (TDP)

lowest temperature at which all cells in a liquid culture are killed in 10 min

thermal death time (TDT)

minimal time for all bacteria in a liquid culture to be killed at a particular temperature

decimal reduction time (DRT)

minutes to kill 90% of a specific population of bacteria at a given temperature

autoclave

steam under high pressure

• 121 C at 15 psi for 15 min

• kills all organisms and endospores

• steam must contact the item's surface

pasteurization

reduces spoilage organisms and pathogens by heating materials for a short time

high-temperature short-time (HTST)

72 degrees C for 15 seconds (normal treatment for milk)

Ultra-high temperature (UHT)

140 degrees C for 4 sec

thermoduric

(relatively heat-resistant) organisms survive

filtration

passage of substance through a screenlike material

• used for heat sensitive materials

high efficiency particulate air (HEPA) filters

remove microbes > 0.3 um in diamter

membrane filters

remove microbes > 0.22 um

• pore sizes of as small as 0.01 um are available, which can filter out viruses and large proteins

desiccation

absence of water prevents metabolism

osmotic pressure

uses high concentrations of salts and sugars to create hypertonic environment; causes plasmolysis

ionizing radiation (x-rays, gamma rays, electron beams)

ionizes water to create reactive hydroxyl radicals

• damages DNA by causing lethal mutations

nonionizing radiation (ultraviolet, 260 nm)

damages DNA by creating thymine dimers

principles of effective disinfection

• concentration of disinfectant

• organic matter

• pH

• time

disk diffusion method

• evaluates efficacy of chemical agents

• filter paper disks are soaked in a chemical and placed on a culture

• look for zone of inhibition around disks

phenol and phenolics

injure lipids of plasma membranes, causing leakage

• strong antibiotics

• basically punch holes in plasma membrane

halogens: Iodine; TINCTURE

a solution in aqueous alcohol

halogens: iodine; IODOPHOR

combined with organic molecules

• impairs protein synthesis and alters membranes

chlorine

oxidizing agents; shut down cellular enzyme systems

• bleach: hypochlorous acid (HOCl)

• chloramine: chlorine+ammonia

• also impairs protein synthesis and alters membranes

alcohols are only effective above ____

60%

______ is used to prevent ophthalmia neonatorum for babies

silver nitrate

aldehydes

inactive proteins by cross linking with functional groups

• used for preserving specimens in medical equipment

_____ is used to preserve dead bodies and it crosslinks proteins causing a huge ball of gunk that bacteria is unable to break down

formaldehyde

oxidizing agents

used for contaminated surfaces and food packaging

• O3, H2O2 (hydrogen peroxide known as powerful oxidizing agent), and peracetic acid