L9: Control of Microbial Growth Flashcards
sepsis
refers to microbial contamination (i.e. wound sepsis, septic shock, septic tank)
asepsis
absence of significant contamination; prevents microbial contamination
sterilization
removal of all microbial life
commercial sterilization
defined by measures to kill Clostridium botulinum endospores (most lethal contaminant of food)
disinfection
removing pathogens/pathogenic microbes
antisepsis
removing pathogens from living tissue
sanitization
lowering microbial counts
bacteriostasis
inhibiting bacterial growth but NOT killing
What are the 2 factors in controlling microbial growth?
time
temperature
Characteristics of Clostridium (C.) botulinum
obligate anaerobes
die in oxygen
are endospores
very dangerous
Bacterial populations die at a __________ under a given set of conditions
constant logarithmic rate
What does bacterial death rate depend on?
number of microbes
environment (conditions)
time of exposure
microbial characteristics
What are the 3 actions of microbial control agents?
alteration of membrane permeability
damage to proteins
damage to nucleic acids
What are the 5 main physical methods of microbial control?
heat
filtration
desiccation
pressure
radiation
HEAT: thermal death point (TDP)
lowest temp at which ALL cells in a culture are killed in 10 min
HEAT: thermal death time (TDT)
minimal time of a particular heat treatment required to kill ALL cells in a culture
HEAT: decimal reduction time (DRT)
minutes required to kill 90% of a population at a given temperature
HEAT: autoclaving definition
use of heat and pressurized steam to kill moderately to highly resistant pathogens
HEAT: traits of autoclaving
moist heat denatures proteins
121 deg. C > 15 psi
steam > dry air
do NOT stack
HEAT: The temp. req to kill bacterial endospores, fungal spores, and inactivate viruses
121 degrees Celsius
HEAT: why is it better to NOT stack containers while autoclaving?
small container = lower surface:volume = heat can penetrate more easily
large container = higher surface:volume = more difficult for heat to penetrate
HEAT: pasteurization
“incomplete sterilization” that uses low heat over a long time; reduces spoilage pathogens
HEAT: function of pasteurization
to kill MOST microbes without compromising flavor, denaturing proteins, or boiling the material
HEAT: dry heat sterilization
kills via oxidation
HEAT: hot-air sterilization
hot, dry air at a longer time (dry air conducts heat poorly compared to steam)
HEAT: what temp and time does hot-air sterilization need to be?
170 degrees Celsius for 2 hours
HEAT: flaming
method to inoculate loops and cell spreaders using a Bunsen burner
HEAT: incineration
typical method for disposing medical waste
HEAT: what temperatures best kill vs. best inhibit microbial growth?
high temperatures better for killing
low temperatures better for inhibiting
HEAT: refrigeration
microbes grow slowly
HEAT: deep freezing
microbes stop growing but may die
HEAT: lyophilization
freeze-drying
FILTRATION: how does filtration remove microbes?
forces liquid or air through a filter so that particles too large to pass through particles will be retained/contained
FILTRATION: high-efficiency particulate air (HEPA)
removes microbes greater than .3 microns in size
FILTRATION: .2 micron membrane filtration
removes microbes larger than .22 microns
DESSICCATION: what is dessication?
drying or smoking, which prevents microbes from metabolizing (metabolism)
DESSICATION: example?
jerky
PRESSURE: osmotic pressure
use of hypertonic solutions to suck water out of a cell, causing plasmolysis
PRESSURE: high pressure
denatures proteins
RADIATION: how does radiation control microbial growth?
damaging microbial DNA
RADIATION: ionizing radiation
damages DNA by ionizing water to release OH
RADIATION: examples of ionizing radiation?
X-rays
gamma
electron beams
RADIATION: examples of using ionizing radiation?
bacteria (Deinococcus radiodurans) that survive in the Chernobyl exclusion zone, which have an extra DNA-repair capability
sleeves of plastic Petri plates radiation-sterilized after packaging
RADIATION: nonionizing radiation
damages DNA via UV (ultraviolet) at a wavelength of 260 nm, which creates thymine dimers
RADIATION: microwaves
damages DNA and kills by heating
What are the principles of effective disinfection?
concentration of disinfectant
amount of organic matter present
PH and time
What is the dilution test?
detection for bacteria post-treatment
DILUTION TEST: what is the first step?
metal rings dipped in test bacteria and dried
DILUTION TEST: second step?
dried cultures placed in disinfectant at 20 degrees C for 10 min
DILUTION TEST: third and final step?
rings transferred to culture media to determine whether bacteria survived treatment
What method is used to evaluate a disinfectant and antibiotics?
disk-diffusion method
What is the process of the disk-diffusion method?
- filter paper disks are soaked in a chemical and placed on a culture
- look for zone of inhibition around disks
What are the 8 chemical methods for microbial control?
- phenols
- biguanides
- halogens
- alcohols
- heavy metals
- surfactants (surface-active agents)
- sterilants
- food preservatives
PHENOLS: phenol/phenolics
an aromatic/phenyl (6-carbon) ring w/ a hydroxyl group attached (–OH); one of the oldest disinfectants
PHENOLS: phenol/phenolics examples?
“old school” phenol, carbolic acid(semi-carcinogenic)
Lysol (phenol + soap chemicals)
PHENOLS: bisphenols
contains 2 phenol groups connected by a bridge
BIGUANIDES: biguanide definition
chlorhexidine; disrupts plasma membranes
BIGUANIDES: biguadine function
surgical hand wash
preoperative skin prep
HALOGENS: what are the 2 types of disinfectant halogens?
iodine
chlorine
HALOGENS: iodine function
alters protein synthesis and membranes
HALOGENS: iodine types?
tinctures
iodophors
HALOGENS: iodine - what are tinctures?
iodine in aqueous alcohol
HALOGENS: iodine - what are iodophors?
iodine combined w/ organic molecules
HALOGENS: chlorine function
“best” for all-purpose disinfecting
HALOGENS: chlorine types?
bleach
chloramine
oxidizing agents
HALOGENS: chlorine - active ingredient in household bleach?
hypochlorous acid (HOCl)
HALOGENS: chlorine - chloramine?
Cl + ammonia; is extremely dangerous (often accidentally created when combining different cleaning chemicals)
HALOGENS: chlorine - oxidizing agents?
damages and shuts down cellular enzyme systems
ALCOHOLS: alcohol definition
1 or more hydroxyl bound to a saturated C; requires some water (aqueous solution)
ALCOHOLS: alcohol functions
denature proteins
dissolve lipids (membranes)
ALCOHOLS: alcohol examples?
ethanol, isopropanol
ALCOHOLS: alcohol is most effective and least effective on which pathogens?
most effective: viruses w/ lipid envelopes
least effective: endospores and non-enveloped viruses (has no effect)
ALCOHOLS: alcohol is more effective when…?
put in an aqueous solution
ALCOHOLS: what is the ideal percentage range of alcohol concentration in a disinfectant?
60-95%
HEAVY METALS: what elements/heavy metals are used for disinfecting?
Ag (silver)
Hg (mercury)
Cu (copper)
Zn (zinc)
HEAVY METALS: oligodynamic action
the ability of small amounts of certain (heavy) metals to kill microbes; small amounts of heavy metals have antimicrobial activity
HEAVY METALS: heavy metal function?
denature proteins
HEAVY METALS: examples?
Ag solutions used to disinfect bacteria in eyes
mercuric chloride prevents mildew in paint
zinc chloride in mouthwash
SURFACTANTS: surfactant/surface-active agent definition
an amphipathic molecule comprising lipids and proteins that reduces surface tension and increases spreading
SURFACTANTS: surfactant functions
“degerming’
damage/disrupt plasma membranes (i.e. sanitizing anions)
bactericidal (kills bacteria)
denature proteins
SURFACTANTS: surfactant/surface-active agent types?
soap
acid-anionic detergents
cationic detergents
quats/quaternary ammonium compounds
SURFACTANTS: examples?
ammonium (cationic detergent)
benzalkonium chloride (Zephiran, a quaternary ammonium compound)
STERILANTS: sterilant definition
a disinfectant that kills ALL microbes, including spores
STERILANTS: what is the #1 main function of sterilants?
sterilize (sensitive) medical equipment; some types of sterilants may have additional functions
STERILANTS: what are the 5 types of sterilants?
aldehydes
gaseous sterilants
gas-discharge plasma
supercritical CO2
peroxygens
STERILANTS: aldehydes
inactivate proteins by cross-linking w/ functional groups
STERILANTS: aldehyde additional function
preserving specimens
STERILANTS: aldehyde examples
glutaraldehyde
formaldehyde
ortho-phthalaldehyde
STERILANTS: gaseous sterilants
replaces H atoms of a chemical group w/ a free radical
cross-links nucleic acids and proteins
STERILANTS: gaseous sterilant additional function
specifically used on heat-sensitive equipment
STERILANTS: gaseous sterilant examples
ethylene oxide
STERILANTS: gas-discharge plasma
electrically-excited gas, which generates free radicals (oxidizing agents)
STERILANTS: gas-discharge plasma additional function
damages protein, DNA, etc.
STERILANTS: supercritical CO2
temp and pressure adjusted so it has gas and liquid properties; is used w/ peracetic acid
STERILANTS: supercritical CO2 additional function
may NOT effectively kill spores
STERILANTS: peroxygens
oxidizing agents
STERILANTS: peroxygen functions
sterilize contaminated surfaces and food packaging
STERILANTS: peroxygen examples
O3
H2O2
peracetic acid
FOOD PRESERVATIVES: what are the 5 main types of chemical food preservatives?
sulfur dioxide
organic acids
nitrite
nisin and natamycin/pimaricin
essential oils
FOOD PRESERVATIVES: sulfur dioxide (SO2)
prevents wine spoilage
FOOD PRESERVATIVES: organic acids
inhibits metabolism; controls molds and bacteria in foods and cosmetics
FOOD PRESERVATIVES: organic acid examples
sorbic acid
benzoic acid
Ca propionate
FOOD PRESERVATIVES: nitrate
prevents endospore germination
FOOD PRESERVATIVES: although nitrate is NOT good for humans…
the danger of nitrate is far overshadowed by the danger of microbial growth
FOOD PRESERVATIVES: nisin and natamycin/pimaricin
prevents spoilage of cheese
FOOD PRESERVATIVES: essential oil
volatile, aromatic plant-derived mixture of hydrocarbons; is an ancient method
FOOD PRESERVATIVES: essential oil examples
peppermint oil
pine oil
orange oil
FOOD PRESERVATIVES: essential oils - microbial action is primarily due to…?
phenolics and terpenes
FOOD PRESERVATIVES: essential oils have stronger antimicrobial activity against…?
G+ bacteria
What disinfectants are best for endospores?
Cl (bleach)
glutaraldehyde
What disinfectants are best for mycobacteria?
phenolics
halogens (iodine)
glutaraldehyde
What disinfectants are best for prions?
phenol
*incineration (extreme heat)
Why are there so few treatment methods for prions?
prions are technically nonliving and already denatured, so most disinfectants are inapplicable;
What disinfectants or disinfecting methods are best for norovirus?
bleach
autoclaving
What are the unique traits of norovirus?
have tough protein capsids
anything contaminated must be disinfected w/ bleach or stripped/disposed
Sterilization standards in food canning and the food industry in general are focused on what?
the destruction of endospores
Endospore examples?
Clostridium botulinum
Clostridium difficile
