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Chapter 11 - Types of Disinfectants
Early 1800’s – chloride of lime; iodine ; Today – 10,000 antimicrobial chemical agents
Germicidals are evaluated according to effectiveness
1. High Level Germicidals – for invasive medical devices – catheters, implants etc
2. Intermediate Level Germicidals – for things that are non-invasive, but contact mucous membranes
- respiratory equipment, thermometers, etc
3. Low Level Germicidals – furniture, electrodes, straps, etc. – non-invasive – don’t touch mucous
membranes
Halogens – (Small, non-metallic elements)
 The active ingredients in nearly 1/3 of all antimicrobials marketed today; “cidal” action
1. Chlorine – used for about 200 years

chlorine + water --> hypochlorous acid ( a strong oxidizer); must be mixed with water

Chlorine liquid or gas – disinfection of drinking water; waste water, sewage pools;

Sodium Hypochlorite ( bleach) – sanitization – dairies; food processing equipment, utensils,
dialysis machines; drinking water; surfaces contaminated with blood or body fluids - use 10%
bleach
2. Iodine - one of the oldest & most effective disinfectants; inactivates proteins

Uses: - on skin and wounds; on inert surfaces

tincture – prepared as iodine mixed in solution of alcohol

iodophor - combined with organic molecule ( often povidone - a wetting agent) e.g. Betadine;

Iodine tablets – emergency disinfection of drinking water
Phenols and Phenolics -
Damages plasma membranes and cell walls; inactivates enzymes

Strongly “cidal” but not good against spores

Toxicity is a problem; skin irritation; odor
1. Phenol -(carbolic acid) – a coal tar derivative
 Joseph Lister – (1867)- for surgical infections; operating room; surgical instruments
 Uses: - throat lozenges, throat sprays; drains, cesspools, animal quarters
2. Phenolics - phenol derivatives; less irritating to skin, milder odor
 usually combined with soap or detergent
 Lysol - good surface disinfectant
 Hexachlorophene (pHisoHex) - surgical and hospital scrub
 Triclosan – commonly used in antibacterial soaps
 Chlorhexidine (Hibiclens ) - surgical scrubs; skin preps, body wash, eye solutions – safer than
other phenolics
Alcohols
 Coagulates proteins; disrupts membranes; dissolves lipids
 Uses: - degerming skin ( before injection, venipuncture etc.)
 Only ethyl and isopropyl are suitable for microbial control ( 70% solutions)
 Kills bacteria & fungi and enveloped viruses ( not good for endospores)
 Not good on wounds - coagulates proteins - bacteria grow in the protein clots
 Solvent for Tinctures - other agents perform better when dissolved in alcohol than in water.
Peroxygens (Oxidizing Agents)
1. Hydrogen peroxide - antiseptic; common in home use
 Decomposes in presence of light, metals or catalase
 toxic form of oxygen – kills bacteria, viruses, fungus and spores
 not good for open wounds - slows healing (broken down by catalase in human cells)
 excellent disinfectant ; surfaces; contact lenses; coatings on food packaging ; instruments used in
invasive medical procedures ( e.g. endoscopes)
 antiseptic – skin, wounds, bedsores -- useful for irrigating deep wounds - released oxygen
inhibits growth of anaerobic bacteria
Surface Active Agents ( Surfactants )
 Mostly soaps and detergents - breaks oily secretions into tiny droplets
 De-germs but can never sterilize
1.
Quaternary Ammonium Compounds (QUATS)
 Based on ammonium ion (NH4+)
 detergents which act as surface active agents ; disrupt the plasma membrane
 Not effective against M. tuberculosis, hepatitis virus, Pseudomonas, or spores
 Pseudomonas sp. (a gram negative bacteria) actively grows in quats - problem in hospitals –
can only be used for low-level disinfection – not for instruments
 Greatly inhibited by the presence of organic material
 used as detergents; floor scrubs; surface cleaners
 Zephiran; Cepacol - mouthwashes, throat sprays
Heavy Metals and Their Compounds
 mercury, silver, gold, copper, arsenic, zinc
 have antimicrobial effects in very small amounts ; denature proteins
 Good against many types of bacteria, viruses, fungi, algae, protozoa – not against spores
 Drawbacks
o Toxic to human cells, even in small quantities
o ingested, inhaled, absorbed through skin
o allergic reactions
1. Silver
 Silver nitrate solution - antiseptic; given to newborns to prevent gonorrheal infections of eyes
 silver ointments – burns
 silver ions - wound dressings(burn patients), catheters, bandages; plastics, steel, toilet seats,
stethoscopes, refrigerator doors
2. Mercury compounds - broad spectrum
 Organic compounds
o mercurochrome - antiseptic for mild cuts – not very effective
o Merthiolate – a tincture – effective – not for broken skin – prevents healing
o Preservatives in cosmetics, ophthalmic solutions
Aldehydes Cross-link proteins, thereby inactivating them - among most effective antimicrobials
1. Glutaraldehyde
 Highly effective sterilizer and high-level disinfectant
 Dental instruments, to preserve vaccines,
 Cidex - hospital instruments; respiratory therapy equipment
2. Formaldehyde – sharp, irritating gas
 Formalin - 37% aqueous solution of formaldehyde gas - inactivate bacteria and viruses in
vaccines; preserves biological specimens, embalming fluid – highly toxic - carcinogenic
Gaseous Sterilizers
Used in a chemiclave - an enclosed chamber similar to an autoclave; sterilize without heat or liquid
1. Ethylene oxide – damages DNA
 highly penetrating but slow acting
 spacecraft; plastic materials, delicate instruments, electronic gear; mattresses; sugar,spices, dried
foods and drugs
2. Chlorine dioxide – disrupts proteins
 Drinking water, wastewater, food processing equipment
 Used to disinfect rooms ( e.g., to disinfect Senate offices after anthrax attacks, 2001)
Dyes
1. Crystal Violet ; Malachite green
 effective against gram positive bacteria and fungus
 used in topical solutions or ointments for skin infections ( e.g., ringworm)
Acids and Alkalis
Extremes of pH can kill or inhibit microbial growth
Corrosive, caustic, hazardous
1. Ammonium hydroxide – detergents, cleaners, deodorizers
2.
Organic acids – food preservatives
 Acetic Acid (vinegar)
 Lactic acid – added to sauerkraut and olives
 Calcium propionate - prevents molds and Bacillus from growing in bread
 Sorbic acid; potassium sorbate; sodium benzoate - prevent mold growth in acid foods