CHEMICAL DISINFECTION

Historical Review
• Wine used externally & internally
• 1363 - Brandy used for military dressing
• 1830 - Tincture of iodine US
pharmacopoeia
• 1832 - Creosote (phenol) “I preserve flesh
“in Greek
• 1854 - Hypochlorites used in hospital wards
• 1905 – Kinnaman, disinfectant action of
chemicals

Definitions
• Sterilization
• Disinfection
• Antisepsis
• Decontamination

Definitions
• Sterilisation – Process by which an
article, surface or medium is freed of all
living microorganisms either in the
vegetetative or spore state.
• Disinfection – Destruction or removal of
all pathogenic organisms, or organisms
capable of giving rise to infection.

Definitions
• Antisepsis – Prevention of infection,
usually by inhibiting the growth of
bacteria in wounds or tissues.
•Decontamination – Process of
rendering an article or area free of
contaminants eg.microbial, chemical
etc.

Properties ; Ideal Disinfectant
• Wide spectrum of activity
• Active in presence of organic matter
• Effective in acid & alkaline media
• Speedy action
• High penetrating power

Properties ; Ideal Disinfectant
• Stable
• Compatible with other antiseptics &
disinfectants
• Non corrosive, non irritant & non toxic
• Cheap & easily available
• Safe & easy to use

Modes of action
• Protein coagulation
• Disruption of cell membrane
• Removal of sulphydryl groups essential
for enzyme functioning
• Substrate competition

Levels of Disinfectant Action
BACTERIA FUNGI VIRUSES
Disinfectant
Level Spores
Tubercle
Bacillus
Vegeta
tive
Cells Fungi
Non
lipid
and
Small
Lipid
and
Medium
Sized
High +‡ + + + + +
Intermediate S + + + ±(in
high
conc|)
+
Low - - + ± ± +

Classification
Low & Intermediate
level
• Halogens
• Alcohols
• Phenols
• Dyes
• Metallic salts
• Surface active agents
High level
• Aldehydes
• Peroxygen Compounds

PRIONS
BACTERIAL SPORES
MYCOBACTERIA
PARASITIC CYSTS
SMALL NON ENVELOPED VIRUSES
TROPHOZOITES
NON SPORULATING GRAM NEGATIVE BACTERIA
FUNGI
LARGE NON ENVELOPED VIRUSES
NON SPORULATING GRAM POSITIVE BACTERIA
ENVELOPED VIRUSES
HIGHEST
LOWEST

Halogens
• Chlorine & chlorine compounds
– Chlorine
– Hypochlorites
– Chlorine dioxide
– Chloramines
• Iodine & iodine compounds
– Iodine & iodide
– Iodophors
– Preparations producing iodine in situ

Chlorine & Chlorine Compounds
• Mechanism of action
Cl + H2O → HOCl + H++ Cl-
Oxidize thiol gps and halogenate –NH2 gps in proteins
• Advantages
– Low cost
– Rapidity of action
– Broad antimicrobial activity
• Disadvantages
– Corrosiveness
– Inactivation by organic matter
– Chemical instability.

Practical applications
• Water treatment
– Drinking water
– Swimming pools
– Sewage & waste water
• Disinfection of open wounds & dental therapy
– Hypochlorites & organic chloramines
• Disinfection of equipment, instruments & laundry
• Decontamination
– Blood and body fluid spills
– Bedpans, urinals, and kidney bowls
– Culture spills in the microbiology laboratory

Iodine & Iodine Compounds
• Mode of action
– Oxidation of -SH group
– Iodination of phenolic & imidazolic groups of
amino acids
• Iodophores
– Complex of iodine with a carrier
• Carriers – neutral polymers e.g. polyvinylpyrrolidinone
(Povidone Iodine)
• ↑ solubility of iodine
• Sustained release reservoir

Iodine & Iodine Compounds
• Topical antiseptics
• Topical Iodine soln (aq soln of 2% Iodine & 2.4% NaI )
• Tincture of iodine (2% Iodine & 2.4% NaI in aq ethanol)
• Lugol’s iodine (5% Iodine with 10% KI)
• Povidone iodine
Preoperative preparation of skin
Treatment of infected & burnt skin
• Veterinary medicine
• Disinfection of cow’s udder
• Disinfection of water & air

Alcohols
• Ethyl alcohol & isopropyl alcohol (70%)
• Mode of action
– Protein coagulation/denaturation
• Range
– Vegetative bacteria
– Viruses (enveloped)
– Fungus - Methyl alcohol
– Protozoans
• Disinfection of thermometers & stethoscopes
• Skin antiseptics

Phenolic compounds
• Coal tar
– clear soln phenolics
– black fluids
• Fractionation of coal tar
• Synthetic - phenol, cresol & xylenol
• Bisphenols - two phenolic gps e.g.
dichlorophane
• Chlorhexidine

Phenolic compounds
• Mode of action
– At high conc - penetrates and destroys cell wall &
precipitates cellular protein
– In lower conc - inactivates essential enzymes
• Disinfection of environmental surfaces and
noncritical devices
• Chlohexidine
– Skin disinfection
– Surgical hand disinfection
– Obstetrics & gynaecology

Surface active agents
• Amphophilic compounds
• Hydrophilic gp
• Lipophilic gp
• On the basis of charge on polar group
– Cationic (QAC)
– Anionic
• K laurate, Na lauryl sulphate (soaps, shampoos)
– Nonionic
• Stabilizers, wetting agents, detergents & emulsifiers
– Amphoteric/ zwitter ions
• Catonic & anionic charge
• Nonionic at isoelectric pH

Surface active agents (Cationic)
• Mode of action
– Act on the PO4 gp of cell membrane → enter cell →
denature proteins
• Antimicrobial activity
– Gram +ve & Gram –ve at higher conc
– Spores, mycobacteria & viruses – no effect
• Cetavlon(savlon), benzalkonium chloride & cetrimide
• Disinfection of skin, bladder irrigation, diaper rash
• Disadv : Gm -ve bacteria Pseudomonas and Proteus
spp. capable of growing in these solutions

Peroxygen Compounds
• Hydrogen peroxide
• Peracetic acid
• Performic acid
• Perpropionic acid

Peroxygen Compounds
• Mode of action
– Cl- + H2O2
MPO OCl- + H2O
– O2
- + H2O2 → OH + OH- + O2
– H2O2 + Fe 2+ → OH + OH- + Fe 3+
• Range of action
– Bacteria, yeasts , fungi, viruses & spores
• Applications
– Antiseptic
– Odor control in sewage treatment
– Contact lens disinfectant

Gaseous Chemical Sterilization
• Alkylating agents
– Ethylene oxide (ETO)
– Formaldehyde
• Oxidizing agents
– Ozone
– Betapropiolactone (BPL)
– Propylene oxide
– Chlorine dioxide

Ethylene oxide (ETO)
• Mode of action
– Alkylating –NH2, -OH & -SH gps
• Applications
– Heart lung machine
– Respirators
– Dental equipment
– Glass, metal, paper surfaces
• Disadvantage
– Explosive nature
– Carcinogenic
– Mutagenic

Aldehydes
• Glutaraldehyde
• Formaldehyde

Glutaraldehyde
• Saturated dialdehyde
• Mode of action
– Alkylation of sulfhydryl, hydroxyl,
carboxyl, and amino groups
• Contact time - 20 to 90 min
• Chemosterilant - long contact time (6
to 10 hrs)

Glutaraldehyde
• Advantages
– Broad spectrum
– Activity in presence of organic matter
– Non corrosive action on metals, rubber&
lenses
• Disinfection of endoscopes,
cystoscopes & anesthesia equipment
(Cidex 2% soln))
• Dental surgical instruments

Formaldehyde
• Less potent germicide
• Fumigation of wards/ laboratories/ OTs
(150g KMnO4 + 280 ml formalin/1000cu ft)
• Application
– Disinfection of dialysis systems and
hemodialysis filters
– 10% soln used as preservative

Metals
Copper Silver Mercury
Sulphate
Acetate
Citrate
Nitrate
Sulphadiazine
Thiomersa
Mercurochrome
Phenyl mercuric
nitrate
•Fungicide
•Algicide
•Antisepsis •Disinfectant
•Fungicide
•Preservative

Dyes
Aniline
• Brilliant green
• Malachite green
• Crystal violet
• Affected by presence of
organic matter
• Selective agents in
culture media
Acridine
• Proflavine
• Acriflavine
• Euflavine
• Not affected by presence of
organic matter
• Antisepsis
• Gram +ve > gram –ve organisms
• Bacteriostatic

Risk Stratification Of Hospital
Environment
High risk
(Surgical instruments,
endoscopes & catheters)
Contact with broken skin or mucous
membranes/introduced into body
Intermediate risk
(Resp & anesthetic
equipment, thermometers)
Intact skin/mucous membrane/body
fluids
Low risk
(stethoscopes, beddings)
Intact skin
Minimal risk
(floors, walls, ceilings)
Not in close contact

Hospital Decontamination
AIR Atomized propylene glycol, formaldehyde
BATHS, WASH
BOWLS &
TOILETS
Chlorine releasing compounds
Regular cleaning(acids)
BEDPANS &
URINALS
Decontamination
RESPIRATORY
&
ANAESTHETIC
EQUIPMENT
Ethylene oxide
Glutaraldehyde
ENDOSCOPES Glutaraldehyde

Chemical Disinfection Of Surfaces
• Doorknobs, sinks & bed
rails
• Intensive care units,
surgical suites, and
nurseries
• Chlorine compounds
(500ppm), phenol, or
QACs
• Walls and windows
• Phenols, QACs, and
chlorine compounds with
100 to 200 ppm
Densely contaminated
surfaces
Sparsely contaminated
surfaces

BACTERIAL
SPORES
Glutaraldehyde, formaldehyde
vapour, Chlorine dioxide&
peracetic acid
BLOOD BORNE
VIRUSES,
HEPATITIS A &
PRIONS
Glutaraldehyde, 70% Alcohol,
hypochlorites & iodophores
MYCOBACTERIA
Ethylene oxide, glutaraldehyde,
chlorine dioxide
Problem Microorganisms

Testing of Disinfectants
• In vitro tests
– Suspension tests
• Qualitative - Rideal – Walker
- Modified Chick Martin
• Quantitative
– Capacity tests
• Kelsey Sykes test
– Carrier tests
• In use tests

Bacterial
suspension
Disinfectant
solution
Phenol
Subculture a loopful
after contact time
Rideal – Walker Test
Phenol coefficient Dilution of test disinfectant
that sterilizes suspension in
 given time
Dilution of phenol

Testing of Disinfectants
• Modified Chick Martin
– Organic matter – dried yeast or faeces
• Capacity tests
– The ability to retain activity in the presence
of an increasing load
• Carrier tests
– Carrier ( 1 cm2 cotton cloth dipped in
bacterial suspension) transferred to
disinfectant & after fixed reaction time ,
subcultured

In Use Tests
• Microbiological monitoring of
environment
• Sample taken & diluted plated
• Growth of non sporulating bacteria
Inadequate disinfectant

Resistance to Disinfectants
• Intrinsic
– Impaired uptake of the germicide
– Production of biofilms
• Extrinsic
– Plasmids or transposons – inactivate
germicide
– Efflux pumps

Hospital Policy
• Every hospital should implement a formal
written policy for its disinfection and
sterilization procedures
• Which disinfectant should be used for a
particular purpose
• Safety aspects
– Methods for preparing an accurate use dilution
– Correct exposure time for each disinfectant
– The contact times and concentrations
recommended by the manufacturer must be
strictly followed
– Frequency of use

References
• Seymour S Block; Disinfection
Sterilization & Preservation; Vth edn
• Russel Hugo & Ayliffe; Principles &
practice of Disinfection Preservation &
Sterilization; 3rd edn
• R Ananthnarayan; Textbook Of
Microbiology; VIth edn