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
