Controlling Microbial Growth Flashcards
Heat and radiation are examples of what kidn of control method
Physical agents
Sterilzation and disnifection are what kind of control method
(gas) chemical agents
Filtration is a kind of
Mecahnical removal m=of microbes
Sterilization
Destruction/removal of all forms of microbial life from and object
Physical processes of sterilization
Filtration
High temp
Incineration
Irradiation by UV or gamma rays
Chemical processes of sterilization
Ethylene oxide (used in hospitals)
Chlorine dioxide (decontamination of buildings)
Steam sterilization (microbiology)
Mechanical processes of sterilization
filtration
Disinfection
Broad defintion
includes sanitization and antisepsis
Use of chemicals (disinfectants) to kill or inhibit microorganisms that cause disease
Does not kill all microorganisms
Usually toxic and injurious to human tissues
Widely use Chemicals disinfectants:
Chlorine (water supplies)
Phenols,
Biphenols (chlorhexidine),
Alcohols
Iodine
Aldehydes
Quats (quaternary ammonium salts)
Ozone and UV light (newer means)
Sanitization
Related to disinfection, but sanitization only reduces the microbial population to acceptable standards.
Restaurants/cafeterias sanitize eating utensils to acceptable public health standards.
Antisepsis
Related to disinfection, but used on living tissues
Chemicals used to treat or prevent infection of living tissues (still toxic)
Ex.
Alcohol
Iodine
Chlorhexidine
Heavy metals
Antimicrobial agents
Agents that kill or inhibit the growth of microorganisms (cidal or static)
Cide
suffix indicating agent kills organisms
Biocide or germicide kills
Kill microorganisms
Virocide
Inacivates viruses
Static
agent that inhibit growth
Bacteriostatic agent: (inhibits) growth of bacteria
Sepsis
Bacterial contamination
Aesepsis
Absence of significant contamination
Aseptic techniques
Methods that minimizes contamination
Factors affecting antimicrobial effectiveness
Population size: Large the population (Of microorganisms) = Longer to kill
Population composition: Different sensitivity to antimicrobials
Concentration or intensity: Higher conc, = greater effect
EXCEPT alcohol 70% is more effective than 100%
Time of exposure: Longer exposure = more organisms killed
Environmental conditions
High tem (more killing)
Organic material (decreased killing)
Sewage (reduce effeeiveness of disinfectants), biofilms
Microbial chaaraceristics: Spores more resistant than vegetative cells
Is Gram - or Gram + more resistant
Gram - more resistant than Gram + bacteria
Most antimicrobial agents tend to be water soluble, therefore, they cannot easily cross plasma membranes SO Gram - outer layer keeps them out
Pseudomonas aeruginosa - MOST resistant Gram - (Affects burn victims and causes Cystic fibrosis)
Cystic Fibrosis: Protein in mucous layer doesn’t function effectively, therefore mucous layer in respiratory tract becomes thick
Acid-fast or non acid fast more resistant
Acid-fast more resistant than non-acid fast
Mycobacterium TB - Resistant to aqueous baceticide bc mycolic acid layer
Endospores more resistant than vegetative
Endospores MOST resistant bacteria forms
Naked Viruses or Enveloped viruses more resistant
Envolope (if envelope is broken virus dies) viruses tend to be very easy to destroy (when outside the body)
Naked ones have thick protein coats which protects
Covid is a virus with a lipid envolope
Cyst or trophozoite protozoans more resistant?
Cysts (surival structure for eukaryotic organisms) resistant to chlorine in water
–Cryptosporidium cysts resistant to chlorine in water (spread by pigeons)
How quickly and at what rate do bacteria die off?
Bacteria die at constant rate
The higher the conc. the longer it takes
Most resistant to least resistant forms of microorganisms
Prions
Endospores of bacteri
Mycobacteria
Cysts of protozoa
Vegetative protozoa
Gram-negative bacteria
Fungi AND fungal spores
Viruses without envolopes
Gram-positive bacteria
Viruses with lipid envolopes
Most common physical control method
Heat
Why is moist heat more effective
Moist heat is more effective (steam at 100C more dangerous than oven at 325C)
Moist heat
Kills by coagulation of protein
Boiling water does not actually reach as high heat
How does dry heat kill microbes
By oxidation (requires high temps for a longer time)
Approx. conditions for moist heat killing
Yeast is the lowest temperature for 5 mintes
Molds is a higher temperature for 30 minutes
Bacteria is the highest temperature for 10 minutes
But endospores must be boiled for up to 20 hours to kill them
Does pasteurization change the tast
No
What bacteria is milk
Mycobacterium tuberculosis
3 levels of pastuerization
Low-temperature hold (LTH)
62.8°C for 30 minutes
High-temperature short-term (HTST):
72°C for 15 seconds
Ultra-high temperature (UHT):
Process (5 sec cycle 74oC 140°C 74oC)
Autoclave
Saturated chamber with steam
Raise temp to 121oC
Apply pressure: 15 psi for 15 min
Steam condenses on objects (121oC)
Lower pressure to normal before opening chamber
For surgical instruments, chamber is opened before pressure falls for solid objects (surgica instruments) to dry them instantly
3 forms of dry heat
Incineration
Flaming
Oven (170°C, 2 hours)
Two types of mechanical filtration
Depth filtering
Membrane filters
How small do mechanical porte sizes go
.2 micrometers
What does bacteriostatic mean
most pathogens cannot grow
i.e. refridgeration
A bacteria that is an exception to refridgeration being bacteriostatic
Listeria moncyotgenes
What is non ionizing radiation
UV light
Non penetrating
Can damage eyes, DNA
Germicidal lamps for vaccine disinfection
What is ionizing radiation
Gamma rays, X ays, or high energy electron beams
Cause mutation and death
Low level ioninzing radiation > Used on speices certain meats and vegetables
High energy radiation > used to sterilize medical supplies
How is “limiting water” applied to creating a bacteriostatic environment
Bacteria need water to survive
High concentration of salt and sugar in solutions creates a hypertonic environment and thus bacteriostatic
Which kinds of microorganisms most resistant to desiccation and high salt conc.?
Molds and yeasts
How are disinfectants evaluated?
By the disc dilution method
Inoculate bacteria on nutrient agar plates
Place filter discs impregnated with disinfectant on plates and incubate
Measure zones of inhibition
(diameter) to determine effectiveness, larger diameter, greater effectiveness
What type of chemical disinfectant is used in lysol, toothpaste, and is an excellent skin disinfectant with a broad spectrum of activity?
Phenols
What disinfectant is used by desntists, having a low toxicity and thus safe for skin and mucous membranes
Chlorhexidine
What are the major examples of halogens
Iodine
Chlorine
Chlorine gas
chloramines
Who was the pioneer of phenols
Joseph Lister
What is an Effectant chemical disinfectant against S. aureus
Hexachlorophene
(phenol)
What “chemicals” are used for cleaning prior to surgeyr
Alcohols
widely used alchol disinfectant
Ethanol or isopropanol
Alcohol is most afffective at what level
70% aqueous solution
How do heavy metals affect microbes?
Denature proteins
What are examples of surfactants
Soaps, detergents
- Clean but minimal disinfectant
Quat
Quaternary Ammonim compounds
What are quats commonly used in
Mouth wash
Germicidal against most pathogens but not endospores
What kind of bacteria is mouthwash most effective against
Gram +
Hydrogen peroxide is classified as
An oxidizing agent
Under the category of chemical sterilization
What do hospitals use as a chemical sterilant for bedding and mattresses
Ethylene oxide
Chlorine Dioxide
Used to sterilize building and contents of endospores or anthrax
Also used in water treatment
How do oxidizing agents affect microbes
Interfere with metabolism
Ozone category and use
An oxidizing agent used as a primary water disinfectant
Why is a log curve used to graph bacteria death rates
Using a logarithmic scale makes it easier to visualize the population changes at late time points—the same data points that would otherwise be compressed down against the x-axis.
What can lead to C diff
Overuse of antibiotics
What do Healthcare facillities use for a higher level disinfectant than quats
Hypocholorite disinfectants
Disinfectant vs antiseptic
Disinfectant
Use of chemicals (disinfectants) to kill or inhibit microorganisms that cause disease
Does not kill all microorganisms
Usually toxic and injurious to human tissues
Antispectic: Chemicals used to treat or prevent infection of living tissues (still toxic)
Is heating food in the microwave microbial control?
NO
Does lightly heating food kill microbes?
No
Disinfectant used for skin?
No, that’s antiseptic
Least susceptible microbes to sterilization
prions
Does dry heat OR pasteurization sterilize
Only dry heat sterilizes
Which of the following is a limitation of the autoclave?
cannot be used for heat labile materials
Which of the following treatments is the most effective for controlling microbial growth?
140°C for 4 seconds
Chlorhexidine use
for skin antisepsis but not for disinfection of environmental surfaces
microbes is known to be the most resistant to quaternary ammonium compounds?
Members of the genus Pseudomonas
Does alcohol sterilize
No
What bacteria is not effected by quats
Pseudomonas auriginos
Can grow in quats
Semicritical instruments
Contact mucous Membrane and non intact skin
C. diff
Gram positive bacteria
Symptoms of C. diff
Digestive and colon problems
How must C. diff be disinfected
Quats cannot be used, but hypocolrite (Chlorine) based disinfectants used on surfaces that might come in contact with fecal matter
Spaulding rules
Critical (surgical instruments), semicritical, noncritical
Free radicals
Free floating electrons that damage membrane structure, DNA
- Very reactive
What chemical keeps the steaks fresh
Sodium nitrate and nitrite
3 things contributing to HAI
Presence of microorganisms
Immunocompromised individuals
Chain of transmission (people, bedding, equipment)
What do surfactants do
Decrease surface tension or damage lipid membrane
Purpose of soaps
for cleaning but little disinfectant
Why is a 70% ethanol solution more effective than 100%
70% aqueous solutions more effective than 100% alcoholic solutions
Pure ethanol evaporates very quickly
Pure ethanol would cross the momebrane very quickly and react with proteins in the outer cytoplasm (TOO QUICKLY), forming a crust of dead proteins, protecting the cell from further ethanol exposure
70% ethanol reduces effectiveness, slows denaturing process, so no crust forms and more damage done to cell
Is ethanol effective against viruses?
Yes
ALSO effective on lipid envelope and protein envelope (naked) viruses
How is mercury used medicinially
This heavy metal is found in eye drops and in contact lens solutions
What kinds of bacteria are quats effective against
G+
Not effective against endospores or mycobacteria
Ethyline oxide
(Penetrates deeper than liquid alcohol)
Denatures protein
High penetration power
Sterilizes *microbes AND spores (Requires lengthy exposure time)
Used ikn hospitals as chemical sterilant (beddings, mattressses)
Sodium nitrate and nitrite use for people
Keeping steaks fresh
Cleaning a toilet bowl would be considered __________
Disinfecting
Do autoclaves sterilize?
Yes
How could dairy products avoid requiring refrigeration?
Ultra-high-temperature (UHT) treatment
Which parts of the cell are the major targets of antimicrobial agents?
Proteins and cell membranes
why are microbial death curves are typically plotted logarithmically
Most microbial death occurs in the begining
Strategies for microbial growth control for heat labile items?
Filtration (for liquids not gases)
Non Ionizing radiation
Dessication
Ossmotic pressure
How do phenyls afffect microbial growth>
Phenolics exert antimicrobial activity by injuring lipid-containing plasma membranes, which causes the cellular components to leak out of the cell
What phase in bacterial growth is penicillin most effective
Log
Most effective form of microbial growth control
UHT (5 sec cycle 74oC 140°C 74oC)
