Lecture 19-20 Control of Microbial Growth Flashcards
Disinfection
the use of physical or chemical agents to inhibit or destroy microbes
Two types of chemicals used for disinfection
antiseptics and disinfectants
Antiseptics
chemicals applied to living tissue
Disinfectants
chemicals applied to inanimate objects
Examples of antiseptics
hydrogen peroxide and betadine
Example of a disinfectant
lysol
Aseptic techniques
techniques used to prevent microbial contamination of instruments, labs, personnel, and patients in surgery, pharmaceuticals, and food products
Sterilization
destruction or removal of ALL viable microorganisms from an object or habitat
True or False: sterilization removes vegetative cells and endospores
TRUE
Impact of Joseph Lister
used phenol (carbolic acid) as the first antiseptic spray to disinfect surgical rooms
Bacteriostatic
agents that inhibit, but do not kill microbes; often reversible (ex. clindamycin)
Bacteriocidal
agents that kill bacteria (ex. disinfectants & antiseptics)
Bacteriolytic
agents that kill by lysis and release cytoplasmic content (ex. penicillin)
Total cell count
a direct microscopic count (includes both living and dead cells)
Viable cell count
CFU/mL (includes just living cells)
Trend for bacteriostatic control
total cell count and viable cell count equally flatline
Trend for bacteriocidal control
total cell count flatlines while viable cell count decreases (dead cells remain intact)
Trend for bacteriolytic control
total cell count and viable cell count equally decrease
Population death rate is ____.
constant
What is the typically population death rate?
90% of survivors die per unit of time
Decimal reduction time
treatment time for a 1 log decrease in population
What influences decimal reduction time?
population load, environmental factors, and time of exposure
Three types of physical methods for heat control
heat, radiation, and filtration
Dry heat for microbial control involves
flame/incinerate, hot air (oven)
Food irradiation
the use of radiation to kill germs on food
Moist heat for microbial control involves
pasteurize, boil, autoclave
Ionizing radiation for microbial control involves
x-rays, gamma rays, and electron beams
Non-ionizing radiation for microbial control involves
UV light
Standard boiling procudure
100°C for 10 minutes
Does boiling kill endospores?
No, but it kills everything else
Pasteurization
reduces spoliage organisms and pathogens
Standard pasteurization procedure
63°C for 30 minutes
High-temperature short-time pasteurization procedure
72°C for 15 seconds
Ulta-pasteurized proceudre
140°C for 1-4 seconds
How does the autoclave sterilize materials?
by denaturing proteins
Autoclave
steam under pressure
What is the autoclave bad at sterilizing?
heat-labile substances (ex. enzymes, proteins, antibiotics, blood)
Impact of phenol and phenolics
disrupt plasma membranes, inactivate enzymes, and denature proteins (ex. lysol)
Impact of bisphenols
disrupt plasma membranes, stop fatty acid synthesis (ex. prescription lotions, BPA)
Impact of alcohols
denature proteins, dissolve lipids
Is alcohol a good disinfectant without water?
No, needs to be activated by H2O
Use of iodine
used for skin antiseptic
Tinctures
iodine used in aqueous alcohol
Iodophores
iodine used in organic molecules
Impact of iodine
alters protein synthesis and membranes
Typical form of chlorine in disinfectants
hypochlorous acid (HOCl)
Impact of chlorine
oxidizing agent, stops most cellular activities
Use of chlorine as a disinfectant
can disinfect drinking water and swimming pools
Impact of biguanide compounds
destroys the cell membrane
Action of soap
degerming (physical removal of microbe from a limited area)
Action of acid-anionic detergents
sanitizing (lowering microbial counts), damages cell membranes and enzymes
Action of cationic detergents
bactericidal, denature proteins, disrupt the plasma membrane
Impact of heavy metals
heavy metal ions can combine with sulfhydryl groups on proteins and denature them (ex. brass water container)
Disk-diffusion method
used to evaluate the efficacy of a chemical agent
