antiseptics and disinfectants classification , mechanism of action

Friday, March 27, 2020 AMIR SOHAIL
Definitions:
Asepsis:
Sterilization of instruments, dressing materials
etc. through use of heat or radiation
Fungicide:
A substance that destroys fungi
Sporicides:
Destroy spores

Friday, March 27, 2020 dr. ovais
Sanitizer:
Reduces number of bacterial contaminants
to a safe level
Preservatives:
Prevent decomposition by either chemical
or physical means
Deodorants:
To remove foul odors

Cleansers - to remove foreign material
Antiseptics - applied to living tissue to kill
microbes or to inhibit their growth
Disinfectants - to kill or inhibit
microorganisms on inanimate objects

Antiseptics!
Applied to living tissues for killing bacteria
or to inhibit their growth
Static or cidal effect on organisms
Safe limits for public health sanitization
Complete destruction of microbes
sterilization

Disinfectants!
Germicidals applied to nonliving materials
Are very toxic for parenteral use
Collectively, both antiseptics &
disinfectants termed as germicides or local
anti-infective agents

Some agents in lower concentrations act as
antiseptics but in higher concentrations are
disinfectants

USES!
Topical anti-infectives are used in surgery
for antisepsis of surgical area and surgeons
hands and to disinfect surgical instruments,
operation room & hospital premises.

Disinfectants as for homes & farm
premises, in water treatment, in public
health sanitation & as antiseptics in soaps,
teat dips & dairy sanitizers. Also been used
for treating local infections
Used for microbial control in both
prevention & treatment of diseases.

NOTTTTTTTTTTT to be used as
Most of these locally acting anti-infective
drugs are unsuitable for systemic use
Low margins of safety
Toxic for internal organs

Ideal Properties!
Chemically stable
Rapid in action
Broad spectrum (bact., viruses, fungi)
Potent germicidal activity
Good antimicrobial efficacy

Effective in pus & necrotic tissues etc.
High lipid solubility
High penetrating properties
Long lasting effect
Non-irritant

Should not be toxic to host
Should not impair wound healing
Offensive odor, color & staining properties
should be absent or minimal
Should not corrode or rust instruments
Economic & easily available

Order of killing
Vegetative bacteria
Lipophilic viruses (lipid containing, enveloped)
Fungi
Hydrophilic viruses (non-lipid, non-enveloped)
Mycobacteria (Mycobacterium tuberculosis)
Bacterial spores

Factors affecting antisep. & disinf.
Nature of microbes
Size of infection
Presence of organic matter
Concentration
Temperature & pH

Nature of Microbes:
Efficacy of germicide is influenced by types
of microorganisms.
Vegetative organisms are more susceptible
than the spore forming
G+ve are more susceptible than G-ve
organisms

Size of infection:
In general, higher the level of microbial
contamination, lower is the efficacy of
germicides.
So long period of germicide exposure is
required.

Presence of organic matter:
Presence of pus, blood, and tissue debris at
site of action significantly affects the
germicidal efficacy of many agents.
Faecal and soil contamination makes sheds
difficult to disinfect.

Concentration:
Germicidal action is inversely dependent on
its concentration.
Increase or decrease in concentrations of
some compounds negatively affects the
efficacy.

Temperature and pH:
Certain compounds are more active at
alkaline pH where as some are active at
acidic pH.
High ambient temperature usually results in
increased antimicrobial activity.

Spectrum of Activity:
In general, antiseptics are less toxic to
microbes than the disinfectants
For disinfectants, there is a general scale of
innate resistance of microorganisms to
germicides.
From least resistance to most resistance, the scale is
vegetative bacteria, vegetative fungi and fungal spores,
enveloped viruses, non- enveloped viruses, protozoal
spore, mycobacteria and bacterial spores.
dr. ovaisFriday, March 27, 2020

Classes of Disinfectants:
Low-level disinfectants
Intermediate-level disinfectants
High-level disinfectants

Low-level disinfectants
Rapidly kill vegetative forms of bacteria
and fungi
Used on animal cages, floors and food
bowls

Intermediate-level disinfectants
Agents inactivate tubercle bacillus, most
viruses and fungi.
Used on anaesthesia equipment and
endoscopes.

High-level disinfectants
Agents destroy all microorganisms and have
effectiveness against bacterial spores.
Used on needles, scalpels and scissors

Mode of Action!
By denaturation of intracellular protein
Alteration of cellular membrane
Enzyme inhibition

Classification:
Chemical nature
Mode of action

I-Physical Agents:
1. Heat------dry and moist
2. Light/Radiation------ultraviolet light

II-Chemical Agents:
1. Acids:
a. Inorganic acid---boric acid, HCl,
Sulphuric acid
b. Organic acids---acetic acid, benzoic acid,
salicylic acid
2. Alkalis:---sodium hydroxide, calcium
oxide, calcium hydroxide

3. Oxidising agents:---potassium
permanganate, hydrogen peroxide
4. Reducing agents:---formaldehyde, sulphur
dioxide
5. Alcohols:---ethyl alcohol, isopropyl alcohol

6. Phenol & related compounds:---phenol,
cresol, lysol, hexachlorophene and
resorcinol

7. Halogens & compounds:
a. Iodine & compounds:
i. Iodine---weak soln. of iodine, iodine
ointment, Mandl’s paint
ii. Iodophores:---povidone iodine
b. Chlorine & compounds:
i. Chlorine
ii. Chlorophores---sodium hypochlorite,
calcium hypochlorite, chlorinated lime
etc.

8. Surface acting agents/surfactants
a. Anionic surfactants---soaps
b. Cationic surfactants---cetrimide,
benzalkonium chloride, benzethonium etc.

9. Biguanides:
e.g chlorhexidine and hexamidine
10. Metallic compounds:
a. Silver compds.---silver nitrate
b. Zinc compds.---zinc sulphate, zinc oxide
c. Mercury compds.---mercuric chloride,
thiomersal

11. Dyes:
a. Acridine dyes:---acriflavine
b. Rosaniline dye:---gentian violet, brilliant
green
c. Azo dyes:---scarlet red

12. Antibiotics/antibacterials:
e.g bacitracin, polymyxin B, neomycin, silver
sulphadiazine, mafenide, nitrofurazone
13. Miscellaneous agents:
e.g.ethylene oxide, EDTA (ethylenediamine
tetra-acetic acid)

I- Physical Agents:
1. Heat: Dry or moist heat is widely used
for sterilization and disinfection of
glassware, surgical and laboratory
equipments, dressing etc.
Heat destroys all type of microorganisms
including bacterial spores.

Dry Heat
By using hot air oven
Microorganisms and bacterial spores are
killed.
To destroy all vegetative bacteria,
application of dry heat for 1.5 hrs at 100oC
is necessary
Mold spores are killed by 1.5 hrs at 115oC
Resistant spores by 3 hrs at 140oC

Dry heat destroys microorganisms by
causing coagulation of proteins, oxidation
or incineration.
Dry heat is suitable for oily substances and
dry powders which are destroyed by moist
heat.
Less efficacious for surgical dressings

Moist Heat:
Steam sterilization
Used widely for destroying microorganisms
By using hot water, boiling water, steam at
atmospheric pressure (steaming) or steam under
pressure (autoclaving) generally for 121oC for 15
minutes.
Both vegetative and spore forms of most bacteria
are killed by denaturation and co agulation of some
proteins and enzymes dr. ovaisFriday, March 27, 2020

Surgical dressings, glassware, rubber gloves
and surgical instruments are effectively
sterilized.
Moist heat has more penetrating power than
dry heat

2. Light/Radiations:
Ultra violet light: UV radiations are often
used for sterilization/disinfection of surgical
rooms and naked surfaces such as tabletops.
UV rays destroy vital structures of cells
such as nucleoproteins by which
microorganisms are killed.
G-ve non sporing organisms are most
susceptible.

Common Antiseptics &
Disinfectants:
Phenol, Iodine compounds, Boric Acid,
Acids, Alkalies, Lime, Soaps, Alcohols,
Mercurials, Hydrogen per oxide, Potassium
permangnate, Dyes, Acriflavine,
Formaldehyde, Heat, Dettol etc.

Phenols (Carbolic Acid):
Caustic to tissues
Precipitate Proteins
At 1:90 it can kill many bacteria
Cause convulsions and renal toxicity
Cresol (Lysol), resorcinol and thymol are
some of the derivatives and are antisep. and
disinf.
Hexachlorophene, used in soaps and
creams.

Phenol has wide spectrum of activity
against bacteria, viruses and fungi but
minimal action on spores.
It acts by penetrating and disrupting cell
walls and denaturing bacterial proteins
It is bacteriostatic at conc. of 0.1 -1 % and
bactericidal/fungicidal at conc. of 1-2 %

Iodine Compounds:
2% tincture, as antisep. and disinf.
Stains skin
Irritant to tissues
Complex iodine compounds are less irritant like
povidone-iodine
A 1:20,000 solution kills most bacteria in 1
minute and spores in 15 minutes
Acts by iodinating and oxidising microbial
protoplasm

Iodine is present in solutions, ointments and
paints
0.25 % weak solution is used as uterine and
vaginal douche.
Mandl’s paint is applied over mm of sore
throat
Iodine ointment is widely used as antiseptic
and counter irritant

Boric Acid:
Weak bacteriostatic agent
Applied on delicate tissues
Non-irritating drying substance
Used as aqueous solution 4 %, lotions,
ointments or irrigating solutions.
Boroglycerine paint (30%) is used for
stomatitis and glossitis
Used in dusting powders, eye washes and
ear drops etc.

Acids:
H2SO4 and HCl (0.1-1 N) as
disinfectant
Labs. and Hospitals
Very corrosive
Benzoic acid and salicylic acid
have germicidal and fungicidal
activities

Acetic acid:
0.25 % is useful for irrigation of urinary
tract
1 % for surgical dressings
1-3 % for burn dressings
At 5 %, bactericidal
99 % used as caustic on warts

Benzoic acid:
Non-toxic
Applied on skin on high concentration
Bacteriostatic and antifungal agent used for
preservation of butter, meat, food or drinks.
Used in Whitfield’s ointment to treat
ringworm infection on skin
It also has keratolytic properties

Several other organic acids like salicylic
acid, mandelic acid and trichloroacetic acid
(for warts) are used topically as antiseptic.

Alkalies:
Inhibit most of bacteria and viruses
94% soln. of NaOH to kill most pathogens
including FMDV and parasites
2% acts as disinf.
Liberate OH- ions which have antimicrobial
activity
Potent germicidal, used as disinfectant and caustic
Concentrated solution is used as caustic for
dishorning of calves

Sodium hydroxide
Potent germicide
Soln. is used as disinfectant (2%) and
caustic
Concentrated solution is used as caustic for
dehorning of calves

Soaps:
Gram+
Gram- resistant
Good with Potassium iodide and
Hexachlorophene

Alcohols:
Ethyl Alcohol (Ethanol) and isopropyl
alcohol
More antisep. than disinf.
70% for instruments and syringes
These are highly flammable and may catch
fire during electrocautery or laser surgery.

Hydrogen Peroxide: H2O2
Mechanically removes pus and cellular
debris from wound cavities
Low germicidal activity
Liberates free oxygen
A 3 % soln. is used for wound cleansing

KMnO4
Strong Oxidizing agent, liberates Oxygen when
comes in contact with organic matter or bacteria
Strong antibacterial activity
Astringent, caustic, deodorant
1:3,000 is less irritant
1:1000 solutions are used for douching, irrigating
cavities and cleansing wounds
A 0.02% soln. is used as gastric lavage in poisoning
A 5% soln. is used as astringent

For fumigation, potassium permanganate is
used along with soln. of formaldehyde (1:2)
Used to disinfect water ponds and wells
Not good for surgical instruments due to
rusting property

Dyes:
Brilliant Green:
Surface antisep.
To treat wounds and burns
Crystal Violet:
Antisep., Skin infections due to fungi
0.5% soln. is used for local appliacation

Acridine Dyes:
Acriflavine, euflavine and proflavine
Broad spectrum bacteriostatic and
bactericidals
Non irritant
Antiseptic on skin and mucous membrane
Cream, ointment and emulsion
More active against G+

Acriflavine
0.1 % as emulsion, aqueous or saline
solution, lotion, cream or jelly
Used for burns

Formaldehyde:
For preserving biological material
Externally it is strongly irritant and antiseptic
A 3-8% aq. Soln. is used as disinfectant
Fumes are irritant and does not penetrate well.

Dettol: Chloroxylenol
Antisep. and disinfect.
Highly bactericidal and low toxicity
For skin sterilization, 1:4
For wound cleansing 1-2% soln.
Good for G+
Non corrosive and non irritant

Benzalkonium:
A biocidal agent
Active against bacteria, viruses, fungi and
protozoa
Bacteriostatic or bactericidal
G+ more susceptible
Used in eyewashes, nasal sprays, hand and
face washes, mouthwashes, cleaners,
sanitizers and disinfectants.

Chlorhexidine:
Broad spectrum antibacterial activity
Limited fungicidal and virucidal properties
Used in shampoos, ointments, skin and
wound cleanser, mouthwashes, teat dips and
surgical scrubs.

Silver nitrate:
A caustic, astringent and antibacterial
A 0.1% soln. is bactericidal
0.01% solution is bacteriostatic
Applied on burns to reduce infection
Used to destroy horn buds in calves

Antibiotics:
Bacitracin, plymyxin B, neomycin,
framycetin and tyrothricin.
Sulphonamides like silver sulphadiazine
and mafenide are useful topical antibacterial
agents.
Nitrofurazone is highly efficacious in burns
and for skin grafting.

Microorganisms pathogenic
to humans

antiseptics and disinfectants classification , mechanism of action

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