Chapter 23; Control of Microorganisms

boiling (moist heat)

- 100 C (212 F), takes 10 min to sterilize - kills vegetative bacteria and most viruses and fungi - C. Botulinum and C. perfringens can survive

factors influencing chemical agents

- Nature of disinfectant - Concentration of the disinfectant - Nature of the material to be disinfected - Number of microorganisms present - Type of microorganism present - Length of exposure to disinfectant - Temperature of the disinfectant during exposure - Disinfectant's pH during exposure

UV light

- UV is a form of nonionizing radiation; inhibits microbial growth by damaging cells genetic material

free flowing steam (moist heat)

- fractional sterilization; placed in FF steam for 30 min a day 1. kills veg bacteria; incubated overnight so endo > veg 2. kills new veg bacteria; incubated again 3. kills veg bacteria again

chlorine

- gas combined with sodium hypochlorite -swimming pool maintence

steam under pressure (moist heat)

- pressure, temp and time controlled (autoclave) - higher tems can be reached - 15 lbs of pressure per square inch is 121 C (250 F)

physical methods of controlling microorganisms

- scrubbing - heat (incineration) - cold (freezing) - ultraviolet light (inhibits growth by damaging cells genetic material)

Hexachlorophene

-450 x more effective as a germicide than phenol - common in soap, deodorant, toothpaste - now only available as a prescription

quanternary ammonium compounds

-chemical disinfectant and antiseptic that damage cellular membranes and denature proteins -surfactants -common in every day products

levels of control

1. sterilization: kills all 2. disinfection: kills most but not spores 3. antisepsis: inhibits growth on living tissue

sporicides

Agents that kill bacterial and mold spores

carbolic acid

Joseph Lister (1827-1912) first used phenol as a disinfectant. Phenol aka carbolic acid. -slightly acidic; can cause chemical burns, liver damage, diarrhea, dark urine, and hemolytic anemia

larvicides

Kills larvae, which are the wormlike forms of newly hatched insects.

decimal reduction time

Minutes to kill 90% of a population at a given temperature

glutaraldehyde

Solution used for high-level disinfection and sterilization; germicidal in 10 min and kills endospores in 3-12 hours; inactivates the DNA and RNA of microorganisms

moist heat

boiling, free-flowing steam, and steam under pressure

aldehydes

cause cross-linking that inactivates proteins and nucleic acids

sterilization

completely removes and destroys all life forms

cold

controls microbial growth but does not destroy

iodine

controls microbial growth by oxidizing certain molecules within the microbial cell

cremation

form of incineration; 1600 degrees F (871 degrees C)

chemical methods of controlling microorganisms

germicides, bacteroides, fungicides, larvicides, insecticides, sporicides, viricides

germicides

kill a variety of microorganisms but not spores

bactericides

kill bacteria but not their spores

fungicides

kill fungi and their spores

insecticides

kill insects

viricides

kill or inactivate viruses

dry heat

kills microorganisms by coagulating proteins and breaking hydrogen bonds (fried egg) - requires MORE exposure time than moist heat and less effective - 200 degrees C (392 degrees F) for 1.5 hours (dry heat) = to 121 C (250 F) for 15 min (moist heat)

phenolic compounds

phenol (carbolic acid), cresols (lysol), and hexachlorophene. control microbial growth by denaturing proteins and disrupting cell membranes

cresols

phenolic compounds derived from a chemical known as toluene - 3 forms; ortho-cresol, meta-cresol, and para-cresol - produce lysol

antisepsis

process which microbial growth is inhibited on living tissue to prevent infection

disinfection

reduction of pathogenic agents by chemical or physical means by applying disinfectant to an inanimate object

thermal death time

shortest length of time required to kill all test microbes at a specified temperature

thermal death point

the lowest temperature required to kill all microbes in a sample in 10 minutes

alcohols

used to control microbial growth by denaturing proteins and dissolving lipids in the cell membrane; intermediate level disinfectant

halogens

widely used disinfectants; work by oxidizing the components of microbial cells