Chaper 13: Control of Microbial Growth Flashcards
Sterilization
The complete removal or killing or rendering incapable ofreproduction of all living organisms and viruses
Ex) Filtration for removal
Radiation for rendering incapable of reproduction
Asepsis
sterility
Aseptic technique
things you do to maintain sterility
Sterilixation in an autoclave
transfer of heat from steam, wet heat for contact killing, and denaturazation of proteins/ DNA
-> steam gives deep penetration into matrixes
since killing increases with temperature autoclaves use a steaam temperature greater than normal BP of water (100c ar 1atm, 101kpa, 1bar)
Most autoclaves operate at 15pse or 1.1kg/cm^2 = 115kpa at whihc pressure water boild at 121C
Alternative temp pressure of autoclaves
some operate at 30psi (2.1 kg/cm^2) where the steam temperature is 134C
Why are such high temperatures used in an autoclave
Want to kill the most resistant organism which are the spores of Geobacillus sterothermophilus
death of microorganisms by heat is a first order reaction, the population dies by 90% or 1 log in a characteristic time called the decimal reduction time or D\
usually 6-2x D will reliably sterilize any object
thus the smaller D the shorter teh time to steriize
D declines with increaing temperature
Sterilization of spores
spores are usually the most difficult organims to kill
often spore are heat-resistant, rediation resistant and chemical resistant
Geobacillus stearothermophilus spores are often used due to extreem thermal tolerance, some D100 (decimal reduction time at 100C) in minutes.
D of select Bacillus spp.
B. sterothemophilus 46
B. licheniformic 24
B. anthracis 5
B. cereus 0.8
E. coli sterilization
vegitative cells of mesophiles are fairly heat-sensitive
Dry heat
For objects that do not contain water
glass, steel
for water insoluble products such as oils and fats
can melt or light some things on fire :(
also, if liquid is in a closed vessel will blow up
not as efficient or reliable as moist heat
Hours instead of minutes
UV radiation
260nm
damaging DNA => TT dimer, during replication DNA pol will stall at the dimer. DImer can be repaired (error prone repair leads to mutations)
=> replicaiton stalls are mutations can be fatal
non-ionizing
poor penetration, surface sterilization only
water, air and surface (stainless steel and plastics) sterilizaiton
Ionizing radiation
Xrays (from Co 60), gamma and electron beams from
good penetration throughout food and containers, only really stopped by thick layers of lead an concrete
double-stranded DNA breaks
free radical production
safetly concern due to long life free radicals
Co^60 gamma radiation
Ethylene DIoxide
gas
several hours exposure ar mild temperatures
good for heat sensitive items
bulk items
stuff needs to be porous
leaves a residue
Purpose of disinfectants
reduction in the population of microorganisms to a reasonably safe level
removal, killing or inhibition of microorganisms whihc are pathogenic
Types of disinfectants
phenol
bis-phenols
heavy metals
halogens
hypochlorite
iodine mixtures
chlorohexadine
ethanol 70%, isopropanol 70%
quaternary ammonium compounds
alkylating agents
bis-phenols
benzyl-chlorophenol and triclosan
anti-microbial but sate for human skin
=triclosan which is an antiseptic and a disinfectant (probably a carcinogen)
heavy metals
mercury, silver, copper, nickel
halogens
chlorine gas, chloramines and bromine
chloride dioxide or in salts
good for water treatment in potable water
disinfected in water
ammonium compounds
QUATs
quaternary ammonium compounds a N+ atom with 4 long chain alkyl groups and a chloride ion
detergents, cause fats to solvate in water, destroy membranes, and denature proteins.
good against envalope virues, but not naked viruses cause they dont have that lipid envalope
spreads well, breaks the surface tension of water
not volatile, so they do leave a residue.
good for cleaning surfaces
industrial and commercial settings (hospitals and food processing plants)
(the most important one on this list)
alkylating agents
covalently modify DNA and protiens
not used very much
formaldehyde, gluderaldehyde
beta propionolactone (BPA) = inactivating viruses in samples
o phthaladehyde (OPA)
Antiseptic
an antimicrobial compound (disinfectant) which is safe for contact with human skin
antibacterial, antifungal, not so much antiviral
ethanol and hydrogen peroxide but these are not really safe for contact except at low concentrations and low contact time
soap and detergents
sanitization
reduce the number of microorganisms to a defined safe level
phenols
numbs pain, in anti ithcing creams
toxic, corrosive, carcinogen, leaves a residue
silver
long history as a antibacterial agent
silver cutlery, plates and drinking glasses
not very toxic, and does not dissolve in water
silver nitrate is used to today
= an oxidizing agent for things like cold sores
=caterizes wounds
= also used in eyedrops to prevent blindness from sexually transmitted diseases
Copper
poor mans silver
good b/c it is maliable
not as effective as silver, but cheaper
nickle
an even poorer mans silver
mercury, cadmium, lead, and tungston
good b/c antimicrobial, but are however, toxic
ppl used use salversan, which is an organic mercury salt
= was very good for treating STDs especially syphallis
bleach
need to make your working solution each day (0.5 - 1%)
most of the bleach ends up using their disinfecting power oxidizing organic materiual, protiens etc. not the infectious agent :(
iodine
iodine mistures or iodine salt + a wetting agent b/c iodine doesn’t dissolve or spread very well
skin disinfecteds, oxidizing agents, but not very good ones
alcohols as disinfectents
ethenol and isopropanol
used because these are the bois that are soluable in water
100% is bad, because they dehydrate the cells and end up not kiling them
70% is good, below is bad.
strip membranes, denature protiens
not good agaisnt spores or mycobacterium
evaporates and is very flammable or explosive not good for bacteria in orgnaic mateiral like blood
no residue, low surface tension, can flow into cracks
perodixes
surface use
many different types
disinfecting powers will degrade over time
react with metals like iron, and will decompose to water
better than ethanol in things like blood
oxidizing agents
difference between a soap and a detergent
detergents are not ppt our by metals in water (like Ca2+)
detergents are better than soaps
kills naked and envaloped viruses
Contact time and concentration for disinfectants
contact time and concentration are important factors- generallly inverse to each other
indicator organisms (Usually ATCC strains, 1 G+ and 1G- plus Pseudomonas aeruginosa plus Mycobacterium)
=non-pathogenic mycobacterium
=might also include spores, fungi, naked or envalopoed viruses
often contain a surfactant to reduct surface tension of the disinfectant
Pasteurization
heat applied for a long period of time at a low temp
moist heat below 100c
used on heat sensitive fluids like milk, beer and fruit juices
heat denatures and ppt out proteins
milk pasteurization
63c for 30 min
to kill of mesophilic and psycotrophic pathogens
to kill/ reduce the number of bovine tuberculosis, and reduce the numbers of staph aureus and enterics
hihgh temp/ flash pasteurization
72c for 15 sec
purpose of pasteurization
kills pathogens and reduces the total populaiton of bacteria (does not kill all bacteria or kills spores)
main purpose is to slow the rate of spoilage
to kill of mesophilic and psycotrophic pathogens
UHT
ultra high temp pasteurization
high temp, lower contact time
kill more organsims, quicker without degrading the quality of the product
like 85C for 30sec
hot quick, then cool it back down quick
Tyndallization or Fractional Steralization
put the product into a bath of a product that is a temp high enough to kill a pathogen/ vegatative cells for a short period of time.
let rest for a bit, spores become vegatative cells, then treat a second time
repeat the process at least 3 times and upwards fo 5/6 times
steralize the liquid without reaching 100c
Refrigeration and Freezing
slows the growth of most mesophiles
commercial refrigerators operate at 4-8C
Freezing stops metabolism and chemical deterioration at -18c
=> because cells are full of solutes, 0c does not nessecarily freeze cells, but -18c does
freezing may slowly kill bacteria but ice crystal formation may also dehydrate them (dehydrated cells dont die)
=> slow freezing= ice crystal formation= death sometimes
can quick freeze via liquid nitrogen to prevent ice crystal formation and thus desiccation.
sublimaiton in the freezer over time can lead to desiccation
Are most human pathogens psycrophiles or mesophiles
mesophiles
some are pathogens that can grow/ cross the range of mesophile and psycrophiles
obvs mesophiles cause they grow in the human body at 37c
Pressure
high pressure can kill vegetative cells but not as effective against spores
hyperbaric oxygen treatment to kill anaerobes
100+atm
can steralize thing with this
liquids and semiliquid media
expensive
hyperbaric chamber and high pressure to 3atm to kill clostridium species under slightly higher O2 conc.
=> O2 diffuses into body to kill the anaerobe
Desiccation
removal of free water inhibit metabolism
does not necessarily kill bacteria
includes natural dehydration (sun drying) and freeze-drying (lyophilization, -80c and put under a vaccum suich that the water sublimes and is sucked offf via a vaccum pump. often used to steralize vaccines. can also be used to keep bacteria long time in storage, they are protected wioth things like skim milk whihc is known as a cryoprotectant)
decreaces water activity
Water activity
is a measurement of the avalibility of water to an organism
for pure water aw = 1.00
as you add solutes, the water activity decreased (less free water, water becomes bound to water)
this is why you add sugar and salt to things like jam
less free water, those h-bonds cant form
desiccation can decrease water activity by adding high concentrations of solutes such as sugar and salt
Free water
water that can be removed from an object without heat
water that is not bound to proteins and such
non-solvating water
aw differences between water and fungi
bacteria are more sensitive to free water loss than fungi
most bacteria 0.91 - 0.98
-> can uses these values to see what foods bacteria can or cannot grow on
most yeast 0.88
- > why fungi can grow on bread, baked goods and grains, and cheese
- > not on meats because the lipids on meats are protective
Salt, aw and food fermentation
additon of salt decreases water activity
can prevent to grow of organisms that require higher water activity like pseudomonas and enterobacteriaecae but allow for the growth of lactobacilliaceae
Osmophilic yeast
aw 0.62
=Zygosaccharomyces rouxii
is an osmphillic yeast
is a real problem in things like fruit juice
Filtration
useful for gases and liquids
for air, HEPA (high efficiency particulate air) filtration is used
filter material can capture particles of 0.3um size with 9.997% efficiency (can vary depending on pore size)
liquids can be sterilized by membrane filtration
usually pore size of 0.2um to remove bacteria
Absolute filtration
= if undamaged filter will remove 100% of particles greater in size thatn the normal pore size of the filter
liquid filtration
ultrafiltration (UF)
to remove viruses (lots of variation in virus size, however, if you select for a parva virus, no others will get through cause they are so small)
can be done at low temp
will not damage the liquid you are steralizing (protein type theraputics, sill however lead to some loss since some proteins will stick)
pore size = 0.01um
liquid filtration
depth filters
porous filtration medium which remove partivles throughout the medium rather than just on the top
diatomaceous eath
paper (cellulose)
liquid filtraiton
