Chapter 7: Controlling Microbial Growth Flashcards
sterilization
destruction/removal of microbial life from an object.
Physical processes: filtration, high temp, incineration, irradation by UV light or gamma rays
Chemical processes: ethylene oxine (used in hospitals), chrloine dioxide (decontamination of buildings), steam sterilization (microbiology)
mechanical processes: filtration
disinfection
use of chemicals (disinfectants to kill or inhibit microorganisms that cause disease
does not kill all microorganisms, usually toxic and injurious to human issues
sanitization
related to disinfection, however, sanitization only reduces the microbial population to acceptable standards
restaurants/cafeterias sanitize eating utensils to acceptable health and public standards
antisepsis
related to disinfection
chemicals used to treat or prevent infection of living tissues (still toxic)
common antiseptics: alcohol, iodine, chlorhexidine, heavy metals (silver, mercury)
antimicrobial agents
agents that kill or inhibit the growth of microorganisms (cidal or static)
cide antimicrobial agents
cide: suffix indicating agent kills organisms
* Biocide or germicide: kills microorganisms
* Virocide: inactivates viruses
* e.g. microbiocides for HIV used in spermacides
* Fungicide: kills fungi
static antimicrobial agents
- static: agent that inhibit growth
- Bacteriostatic agent: (inhibits) growth of bacteria
sepsis
bacterial contamination
asepsis
absence of significant contamination
aseptic techniques
methods that minimizes contamination
factors affecting antimicrobial effectiveness (6)
1) Population size: the larger populations, the longer to kill
2) Population composition: Different sensitivity to antimicrobials
3) Concentration or intensity: The higher the conc., the greater the effect
4) Time of exposure longer exposure, more organisms killed
5) Environment conditions: High temperatures (more killing), Organic material (decreases killing) E.g. Sewage, biofilms
6) Microbial characteristics: Spores more resistant than vegetative cells
what is more resistant: gram negative or gram postive? why?
gram negative because they have LPS rich outer membrant to protect against chemical biocides
what is more resistant: acid fast or nonacid fast?
acid fast because they have a thick, waxy layer that makes them resistant
what is more resistant: endospore or vegetative?
endospore
what is more resistant: naked virus or enveloped?
naked virus
what is more resistant: cyst or trophozoite stages of protozoans?
cyst is more resistant
physical control methods
heat: dry and moist
what is an autoclave?
steam sterilizer that operates like a pressure cooker
- operates in a cycle
-saturated chamber with steam
- raises the temp to 121 degrees
-applies pressure 15 psi for 15 mins
-steam condenses on objects
pasteurization
reduces number of pathogens but does not change the taste!
considered a disinfectant
what are the 3 different ways that milk can be pasteurized?
1) Low-temperature hold (LTH)
62.8°C for 30 minutes
used when you dont have a lot of milk to pasteurize
2) High-temperature short-term (HTST):
72°C for 15 seconds
most commonly used when you have lots of milk and it is usually the milk you buy
3) Ultra-high temperature (UHT):
Process (5 sec cycle 74oC to 140°C to 74oC)
packaged in open shelves and doesnt need to be refrigerated- sweet milk
filtration
can reduce microbial population in liquids by sterilizing heat sensitive materials and recudes microbial populations in the air
2 types of filtration
1) depth filtering
2) membrane filters- 0.1mm thick, pore sizes from 0.2 micrometers (bacteria will not be able to pass through these pores)
refrigeration is _______
bacteriostatic where most pathogens do not grow except listeria monocytes
Non ionizing radiation
UV light- not penetrating, can damage eyes and DNA, germicidal lamps for vaccine disinfection
ionizing radiation
gamma rays, x rays, or high energy electron beams, cause mutations and death, low ionizing radiation- used on spices, certain meats and vegetables, high energy radiation- used to sterilize medical supplies
limiting water
desiccation: bacteriostatic: lyphilization used to preserve cultures (removes water from the environment)
osmotic pressure- high con of salt or sugar removes water from the environment and destroys microorganisms
disc dilution methods
-inoculate bacteria on nutrient agar plates
-place filter discs impregnated with disinfectant on plates and incubate
-measure zones of inhibition- the larger the diameter, the more effective the antibiotic is
phenols
-originally used by Joseph Lister
- used as chemical disinfectants
-can be identified by benzene ring with OH attached to it
lysol phenol
Mixture of phenols used as general disinfectant
hexachlorophene phenol
Excellent skin disinfectant
Effective against S. aureus
But is neurotoxic in rats
triclosan phenol
Used in antibacterial soaps and toothpaste
Banned in soaps in US in 2017
Broad spectrum of activity
Chlorhexidine
Disinfectant (member of biguanides)
Widely used by dentists
Also used as skin antiseptic
Low toxicity
Used on skin and mucous membranes
halogens
disinfections: split into iodine, chlorine, chlorine gas, chloramines
iodine halogen
Tincture (iodine+alcohol)
Iodophors (iodine+organic carrier)
Betadine® and Isodine®, Wescodyne
Stain skin and garments
Effect agains all bacteria, spores, fungus and viruses
chlorine halogens
used to disinfect water supplies (active ingredient: Hypochlorous acid)
Effective against wide range of microbes
Disadvantage:
Corrosive
Inactivated by organic matter
Forms chlorine disinfection by-products (DBPs) linked to bladder cancer
chlorine gas
can form bleach (hypochlorite ions) in water
chloramines
chlorine and ammonia
alcohols
disinfectants
split into ethanol or isopropanol
denature proteins and damage cell membrane
used to clean skin
