Chapter 7 - Types of Disinfectants - Microbiology



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

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download