Sterilization & Disinfection
Chemical Agents
Hugh B. Fackrell
chemster.ppt
2
Sterilization & Disinfection
 Definitions
 Bacterial Cell Death
 General characteristics
 Types of Chemical Agents
 Comparisons
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Definitions
 Sterilization
– Complete Destruction of ALL microbes
 Disinfection
– Killing of pathogens on inanimate objects
– physical or chemical
 Antiseptic
– A chemical agent for disinfection of living
tissue
– External skin, mouth vagina
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Definitions
 Bacteriocide
– kill microbes
– also germicide, fungicide, virucide
 Bacteriostatic
– Prevents or stops microbial growth
– also fungistatic, virustatic
 Aseptic(Asepsis)
– Prevent contamination of person or object by
microbes
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Definitions
 Sanitize
– Removal of pathogens from inanimate objects
– Mechanical or chemical cleaning
– need not sterilize of disinfect
 Contamination
– Presence of living microbes on object
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Definitions
 Infection
– Presence of living multiplying microbes in host
tissues
– often pathogenic
 Preservation
– Prevention of spoilage
– Control of Contamination
– Bacteriostatic
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Bacterial Cell Death
Survivors
(log)
1 log decrease = 90% kill
5
1 log
Death rate (D) varies
with bacteriocide
4
3
2
1
D
0
Time (min)
Time(min) to
kill 90%
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Chemical agents
 Wide variety in susceptibility
 Growing cells more susceptible than resting
cells or spores
 Gram +ve more susceptible than Gram -ve
 Mycobacterium (TB) more resistant
 Hepatitis virus very resistant
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General Rule for Disinfection
 Clean then disinfect
– organic matter inactivates many chemicals
 Use at recommended strength
– Undiluted NOT always best
– 70% alcohol better than 100% alcohol
 Prevent contamination of disinfectant
 Prepare fresh
– deterioration after prolonged storage
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Types of Chemical Agents
 Phenols
 Halogens
 Metal ions
 Alcohols
 Detergents
 Alkylating agents
 Ethylene Oxide
 Hydrogen peroxide
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When in doubt about efficiency
of a disinfectant
Get a laboratory test
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Phenols
 Mechanism of action
– Rupture the cell membrane
– Denature enzymes (protein)
 Effective in presence of organic matter
– blood, pus, feces, vomitus
 Good environmental disinfectants
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Phenols (examples)
 Phenol
– corrosive to skin
– smell
– 1% effective disinfectant
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Cresols
– Methyl phenol
– Phenyl-phenol (“Lysol”)
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Chlorinated phenols
 Hexachlorophene
– Effective against Gm +ve
– absorbed through skin
– Toxic to infants if used often
 Pentachlorophenol
– more toxic than above
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Halogens
 Cholorine
 Iodine
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Iodine
 Applications
– Skin antiseptic
– Environmental disinfectant
 Mode of Action
– Iodination of Tyrosine
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Iodine (cont)
 Prepare fresh
– Dark brown - active
– Straw Yellow - inactive
 Clean area first
– organic matter reduces activity
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Iodine Formulations
 Tincture iodine I2 in ethanol
 Aqueous iodine I2 in NaI/KI
 Iodophors (organic)
– I2 in nonionic detergent
• Wesocdyne
– Generally 75 ppm
– Mycobacterium 450 ppm
– Iodoform
• I2 chemically combined
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Chlorine
 Bacteriocide, fungicidal, virucidal
– 2-10 ppm
 Applications
– disinfection of water, sewage etc
 Mode of Action
– Oxidizes proteins
 Features
– corrosive
– smells
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Chlorine /formulations
 Chlorine gas
– Poisonous
– forms HOCl
(hypochlorous acid) in
water
 Applications
– water supplies
– swimming pools
– sewage effluent
 Inorganic chlorine
– Bleach NaOCl
– hypochlorite Ca(0Cl)2
– chloramine
 effective against
– Hepatitis
– HIV
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Metal Ions
 Silver
– 1% AgNO3 eye drops
– gonnorrheal neaonatal opthalmitis
 Mercury
– Hg Cl2 Skin antiseptic
– Mercurochrome
 Copper, zinc
– fungicide, algacide
– pressure treated wood
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Alcohols
 Ethanol
– 70-75% in water best
– absolute less effective
 Isopropanol
– kills Mycobacterium
“Tincture of … “ alcohol used as the solvent
for other ingredient
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Detergents
 Sanitize
– soaps
– neutral detergents
 Disinfect
– Anionic detergents
– Cationic detergents
DO NOT MIX
 More effective with phenol
 Surface active
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Anionic Detergents
 -ve charge
 salts of long chain alkyl or aryl sulphonates
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Cationic Detergents
 + ve charge
 non toxic
Not effective for
Pseudomonas
 inactivated by proteins
– eg cotton fibres
 effective at low concentrations
 Quaternary ammonium compounds
– Benzalkonium chloride
– eg “Zephiran”
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Chlorohexidine
 “Hibitane”
– 4% gluconate
 Emulsion used as a scrub
 Topical application for minor skin infections
– inefficient at high concentrations
 Mode of action
– cell membrane
– denatures protein
– not affected by organic matter
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Alkylating Agents
 Cross link proteins, nucleic acids
– -NH2, -OH,-SH,-COOH
 Formaldehyde
 Glutaraldehyde
 Beta-priopiolactone
 Ethylene oxide
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Formaldehyde
 HCHO
 Toxic
 Irritant
 Gas - fumigant
 Solutions- protein vaccines
– tetanus diptheria
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Glutaraldehyde
 2% glutaraldehyde pH 8
 Exposure time
– 5 min bactericidal
– 10 min kills Mycobacterium, Heptatitis virus
– 10 hr sterilizes
 Applications
– Lensed instruments, tubing, scalpels, inhalators
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Beta-propiolactone
 Carcinogenic
 Unstable
– degrades but leaves no residue
 Applications- sera, vaccines
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Ethylene Oxide
H2C
CH2
O
 Sterilizes heat sensitive or chemcial
sensitive objects
 Flammable, explosive carcinogenic
 Gas sterilizing autoclave
– 3-4 hr, 60 oC, high pressure
– 24 hr room temperature to dissipate gas
– use with CO2 or FREON to reduce explosions
Pregnant women should not be exposed!! 4/13/2015
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Hydrogen Peroxide
 Oxidizing agent
 Disinfectant -6%
– Bactericidal
– Fungicidal
– Virucidal
 Prepare fresh
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Kill curves of various antiseptics
% survivors
Soap & water
Tincture of
Merthiolate
Aqueous Zephiran
Tincture of
Iodine
Tincture of
Zephiran
Time (sec)
70% ethanol
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