Control of Microbial Growth
Chapter 11
I.
Introduction
Vocabulary
Sterile
Disinfect
Antisepsis
Sanitization
Pasteurization
- cide
- stasis
Degerming
Resistance to microbial control
Endospores, protozoan cysts, naked virus, M.tuberculosis, S.aureus,
Pseudomonas, vegetative cells, fungal spores, enveloped viruses, yeast,
trophozoites
Factors that influence death rate
1.)
2.)
3.)
4.)
II.
# of microbes
nature of microorganisms, population, know the enemy
conditions – temp, pH, concentration, mode of action
presence/amount of organic material
Figure ll.1 – Physical methods of control – mechanical
A.)
Heat
1.)
2.)
autoclave – steam under pressure
121°C
15psi,
15-20 min, times vary depending
on size of autoclave and sizes of the load.
kills everything – sterilizes except prions
Applications: any items – media that can withstand the pressure
and temperature such as glass, cloth, gloves, med./surgical
instruments, paper, heat res. Plastics (forceps we used).
: not oil, wax, powder
boiling: moist heat without pressure
100°C for 30' (liquids). Sanitize, disinfection
most vegetative bacterial cells including Mycobacterium &
Staphylococcus, and some viruses
H20, food, clothing/bedding
disadvantages: easily recontaminated
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3.)
Pasteurization – lower # of pathogens without affecting the flavor
classical batch 63°C for 30 minutes
flash 71.6°C for 15 seconds
sterilize UHT ---134°C or 1-2 seconds,
lower pathogens non-spore forms, viruses, enterics
beverages – milk, wine, beer, fruit juice
4.)
incineration
- flame or electric heat coil 800°C – 6,500°C
- kills everything-sterilizes
- including loops/needles / incinerators – syringes, needles, biomedical
waste, bedding
5.)
dry oven
150°C - 180°C for 2-4 hours
sterilization
glassware, powder, oils – not plastics, paper, liquids which
evaporate
B.)
Low temperatures and Desiccation- bacteriostatic
1.)
refrigeration 4°C
freezing 20°C, -70°C - 135°C (deep freezing
all pathogens slowed down, some pathogens killed
Food preservation – culture preservation/mammalian cells
2.)
freeze drying – lyophilization
no ice crystals/preservation food – cultures
natural desiccation of some pathogens kills them but not
endospores, like refrigeration and freezing slows/inhibits growth
due to lack of H2O
C.) Radiation
1.)
ionizing radiation – gamma rays, x-rays, (sterilize)
damages DNA, mutations, cell death
food must be labeled, no radioactivity passed on to consumers
drugs, vaccines, instruments, plastics, gloves, tissue for transplant
operators must wear protective clothing
non ionizing radiation - U.V. light 240nm – 280nm
non penetrating (damage to human cells – skin, retina
causes pyrimidine dimmers T-T, interferes with replication, transcription
fungal cells, vegetative bacterial cells, protests, viruses, endospores (time
of exposure) disinfection
surfaces, public spaces, and food processing plants liquids - H2O,
milk, juice
3.)
microwaves- do not sterilize, the heat from raising the temperature of the
food or liquid is similar to boiling
Filtration - liquids
Course 8m – 0.02 m & smaller pores can sterilize and catch some
proteins but not some toxins
Vacuum pump/presterilized container
Serum blood products, milk, beer, H2O
HEPA filters for air sterilizing
2.)
D.)
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Chemical methods of microbial control
desirable qualities of chemical disinfectants- pg
rapid action, solubility in water or alcohol, stability, non-toxic to tissues, penetrates
inanimate surfaces, active in the presence of organic material, noncorrosive, nonstaining,
deodorizing, affordable, inexpensive to manufacture
Chemicals
1. Halogens- Chlorine and Iodine
Chlorine-many forms, gas, liquid, hypochlorites, chloramines
kills vegetative pathogens, viruses, fungi, endospores with long exposure
disadvantages-inactivated by organic material and sunlight
applicationsgas/liquid-large scale, water, sewage, wastewater
hypoclorites-food equipment, dairies, canneries, pools,
-treat wounds, disinfect bedding, instruments
chloramines- water treatment, wounds, skin surfaces
Iodine-free iodine and iodophors
kills everythings, slowly sporocidal
sensitive to pH and organic matter, but not as much as chlorine
applications2% iodine-topical antiseptic prior to surgery,
5-10%- not safe for skin, but ok to use for plastics, gloves,
inanimate items
iodophors-iodine complexed to polyvinylalcohol-allows for slow
release and less irritating to tissues, Betadine and Isodine
2. Phenol and derivatives-coal tar
kills-above 1% kills everything but very irritating to the skin,
phenolics- kill vegetative bacteria, fungi and many viruses but not
endospores
continue activity in the presence of organic material
applicationsphenol- drains, sewage, animal facilities
phenolics- disinfectant aerosol sprays, Lysol, triclosan
chlorhexidine-bacteriosidal for gm+/gm-, some fungus and viruses,
not endospores but mild and low toxicity so handscrub, neonatal
wash, preservative for eye solutions
3. Alcohols-ethyl alcohol and isopropanol
kills-vegetative bacteria, enveloped viruses, and fungus but not endospores
and nonenveloped viruses
must be mixed with water to be effective- 50%-95%
applicationscheap degerming agent
thermometers, electrodes
4. Hydrogen peroxide-colorless, caustic liquid decomposes in the presence of light,
metals and catalase
kills-bacteriocidal, virocidal, sporocidal, fungicidal
applications3%-wound cleansing, mouthwash, deep wounds(anaerobes)
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35% or 35% peracetic acid- sterilizing cabinets for delicate, tubing
instruments-endoscopes, dental instruments
ozone- disinfect air, water, cooling towers, industrial AC
5. Surface acting agents, detergents, soap
Quaternary ammonium compounds- cationic detergent kills gram positive,
viruses, fungi, algae
low toxicity, stable, cheap, tasteless, odorless
applications-restaurants, food processing equipment, clothing,
mouthwash
Soap-sudsing and wetting properties, mechanical removal of oil, grease, debris
6. Heavy Metal compounds
high molecular weight metals in aqueous, tinctures, ointments,soap
kills- vegetative bacteria, fungal cells, viruses, algae, protozoa but not endospores
disadvantages- toxic, allergic reactions, neutralized by biological fluids and
bacteria develop resistance, environmental considerations limit use
applicationsmercurochrome-useless
silver nitrate- newborn’s eyes, now topical germicides in the mouth
silver sulfadiazine-ointment added to dressings, burns
silver ions incorporated into many plastics and steel
7. Aldehydes-formaldehyde and gluteraldehyde
gluteraldehyde-liquid with mild odor
kills-everything, sporcidal in 3hours, noncorrosive, works in the
presence of organic matter
Cidex-2% applications-respiratory equipment, dialysis, dental
instruments, poultry carcasses, cow’s teats
formaldehyde-irritating gas, 37% formalin
carcinogen and irritating the skin and mucous membranes
8. Gaseous sterilants- ethylene oxide(ETO) and chlorine dioxide
ETO sterilizes 90 minutes-3hours time necessary and residual gas must be
dissipated
disadvantages- explosive and carcinogen
applications-plastics, delicate intstruments, pre-packaged supplies, food and drugs
Chlorine dioxide
sterilizes
applications: drinking water, industrial waste water, food processing
equipment, Senate offices
9. Organic acids and alkalis
prevents spore germination, bacteriostatic, fungistatic, making food safe to eat
application: food preservation
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