week 5 Flashcards
Microorganisms are not killed
instantly
Population death usually occurs
exponentially
Measure of agent’s killing efficiency
Decimal reduction time
Decimal reduction time
time to kill 90% (reduce [bacteria] by 1 log unit)
what to ensure for killing efficiency
Must be sure persister cells (viable but nonculturable/VBNC condition) are dead
Once they recover they may regain the ability to reproduce and cause infection
Reversible and irreversible
Reversible: Bacteriostatic
Irreversible: bactericidal, bacteriolytic
Bacteriostatic: Bactericidal: Bacteriolytic: Optical density: Viable cell count:
Bacteriostatic: just stop growth of cells
Bactericidal: kills cells but doesn’t lyse them
Bacteriolytic: kills and lyses cells
Optical density: Bacteriostatic and bactericidal are the same
Viable cell count: bactericidal and bacteriolytic are the same
Methods for killing microbial cells (5)
sterilization Disinfection/Disinfectants Sanitization Antisepsis Chemotherapy (antibiotics)
sterilization Disinfection Disinfectants Sanitization Antisepsis Chemotherapy (antibiotics)
sterilization: destruction or removal of all viable organisms (no bacteria)
Disinfection: killing, inhibition, or removal of disease causing (pathogenic) organisms but not endospores
Disinfectants: usually used on inanimate objects
Sanitization: reduction of microbial population to levels deemed safe (based on public health’s standards)
Antisepsis: prevention of infection of living tissue by microorganisms
Chemical agents that kill or inhibit growth of microorganisms when applied to surface of tissue
Chemotherapy (antibiotics): kill or inhibit internal microorganisms
Physical methods
Chemical methods
Mechanical methods
Biological methods
Physical methods
Heat
Radiation
Chemical methods
Gas
Liquids
Mechanical methods
Filtration
Biological methods
Antimicrobials
high moist heat
Destroys viruses, fungi and bacteria (including endospores)
Autoclaving
Low moist heat
(pasteurization)
Controlled heating at temperatures well below boiling
Used for milk, beer, other beverages
Process does not sterilize but does kill pathogens present and slow spoilage by reducing the total load of organisms present
UV radiation most bactericidal
260nm is most bactericidal since it is absorbed by DNA
effect of UV radiation
Causes thymine dimers which prevent replication and transcription
UV limited to
UV limited to surface sterilization because it doesn’t penetrate glass, dirt films, water and other substances
Has been used for water treatment
how deep does Gamma radiation penetrate and what does it produce (3)
Penetrates deep into objects
Generates double stranded breaks in DNA, reactive oxygen species, membrane damage
deadliness of gamma radiation
Kills living organisms, as well as bacterial endospores; not always effects against viruses (depends on outer coating of virus)
Used for sterilization and pasteurization of antibiotics, hormones, sutures, plastic disposable supplies and food
what is membrane filtration,
how does it work and for what type of samples
passing a solution through a filter membrane under a vacuum to remove microbes
- used for liquid samples
- similar to collecting bacteria from water
what’s HEPA filter, how does it work, for what type of sample
another form of membrane filtration but for air instead
- high-efficiency particulate air
- used for gaseous samples
phenolics commonly used as
laboratory
and hospital disinfectants
how do phenolics work
denaturing proteins
and disrupting cell
membranes
what do phenolics kill
bacteria, including
Mycobacterium tuberculosis,
fungi and enveloped viruses
Does not kill spores
phenolics effectivity + duration
odor + skin effects
Effective in presence of
organic material, and long lasting
bad smell, skin irritant
phenolics example
triclosan
alcohol usage, what does it kill
Among the most widely used
disinfectants and antiseptics
Bactericidal, fungicidal, but not sporicidal
Kills enveloped viruses
how does alcohol work
Denature proteins and possibly dissolve membrane lipids
alcohol example
ethanol, isopropanol
why is 70% alcohol better than 100%
100% too dry - will dry out bacteria and if it comes in contact with water will come alive again
what is Halogens used for
Skin antiseptic
how do Halogens kill
Oxidizes cell constituents and iodinates proteins
what do Halogens kill
Kills bacteria, fungi, viruses
At high concentrations may kill spores
problems with Halogens
Skin damage, staining, and
allergies can be a problem
Halogens eg
halazone, triiodide (wants to move to anything with double bond)
how do aldehydes work
Crosslink proteins
• Stop metabolic activity
what do Aldehydes kill
Kills most bacteria and
fungi, including spores
Aldehydes eg
formaldehyde, gluteraldehyde
what are Quaternary ammonium
compounds used for
detergents that have antimicrobial
activity and are effective
disinfectants
what do Quaternary ammonium
compounds kill
kill most bacteria, but not M.
tuberculosis or endospores
• kills enveloped viruses, some fungi
safety and inactivation of Quaternary ammonium
compounds
safe and easy to use,
• inactivated by hard water and soap (hard water has many minerals causing it to precipitate)
Quaternary ammonium
compounds eg
Cetylpyridinium chloride (amphipathic), Benzalkonium chloride
what does Hydrogen peroxide kill
Kills most viruses, bacteria and fungi
how does Hydrogen peroxide work
Oxidized proteins, lipids, and sugars
