PHARMACEUTICAL MICROBIOLOGY (BP303T)Unit-III Classification and mode of action of disinfectants. DISINFECTANT Definition: Ideal properties of disinfectants: CLASSIFICATION OF DISINFECTANTS: Based on consistency 1. Liquid (E.g., Alcohols, Phenols) 2.Gaseous (Formaldehyde vapor, Ethylene oxide). Based on spectrum of activity 1. High level disinfectant 2. Intermediate level disinfectant 3. Low level disinfectant .Based on mechanism of action: 1.Action on membrane2.Denaturation of cellular proteins 3.Damage to nucleic acids 4.Oxidation of essential sulfhydryl groups of enzymes 5.Alkylation of amino-, carboxyl- and hydroxyl group. MODE OF ACTION AND APPICATION OF DISINFECTANT Acid and alkalies Halogens Heavy metals Phenols and its derivatives Alcohol Aldehydes Dyes: Quaternary ammonium compounds Detergents and soaps.

1. PHARMACEUTICAL MICROBIOLOGY
(BP303T)
Unit-IiI
Part-4
Classification and mode of action of disinfectants.
Name: Ms. Pooja Deepak Bhandare
Assistant Professor
G H RAISONI UNIVERSITY
SCHOOL OF PHARMACY

2. DISINFECTANT
Definition:
• Disinfection is the process of destruction or removal of microorganisms and
reducing them to a level not harmful to health.
• Disinfectants generally kills the sensitive vegetative cells but not the heat
resistant endospores.
• Disinfection is less effective than Sterilization process
• Usually disinfectants are bacteriocidal. Occasionally it maybe bacteriostatic.

3. Ideal properties of disinfectants:
• Broad spectrum
• Non toxic
• Fast acting
• Odourless
• Surface compatibility
• Economical

4. • Easy to use
• Solubility and miscibility
• Not affected by physical factors
• Stable on storage
• Several terms used to describe the physical processes and chemical agents
employed in controlling microorganisms are as below.

5. CLASSIFICATION OF DISINFECTANTS
Disinfectants are classified on the basis of their consistency, spectrum of
activity and mechanism of action:
• Based on consistency : On the basis of their consistency state of matter,
disinfectant are classified two types
a. Liquid (E.g., Alcohols, Phenols)
b. Gaseous (Formaldehyde vapor, Ethylene oxide)

6. • Based on spectrum of activity
a. High level disinfectant : These disinfectant are used against certain types of
endoscopes and surgical instruments with plastic components e.g. glutaraldehyde
(2%), hydrogen peroxide (6%), acetic acid (0.2%), chlorine compounds etc.
b. Intermediate level disinfectant : These disinfectant may not be effective against
bacterial spores. These disinfectant are used for disinfection of laryngoscope and
fiberoptic endoscopes e.g. alcohol, iodophores, phenolic compound etc.
c. Low level disinfectant : These disinfectant are used against items which come in
contact with the patient, such as stethoscopes, electrocardiogram electrodes, etc. e.g
quaternary ammonium compounds, phenols, hydrogen peroxide solution, alcohol,
etc.

7. • Based on mechanism of action
a. Action on membrane: These disinfectant act on plasma membrane of
microorganisms and destroy it. They mainly active in combination of water
E.g., Alcohol (ethanol , isopropanol), detergent
b. Denaturation of cellular proteins: These components mainly denature of
protein and enzymes of the cell wall (E.g., Alcohol, Phenol)
c. Damage to nucleic acids : Disinfectant having alkylating action mainly act on
proteins and damage of nucleic acid (E.g., Ethylene Oxide, Formaldehyde)

8. d. Oxidation of essential sulfhydryl groups of enzymes : These
components mainly produce destructive hydroxyl free radicals that attack
membrane lipid, DNA and other cell components. (E.g., H2O2, Halogens)
e. Alkylation of amino-, carboxyl- and hydroxyl group: These
components mainly responsible for alkylating the amino, carboxyl,
hydroxyl, and sulfhydryl groups in the enzyme and protein molecules (E.g.,
Ethylene Oxide, Formaldehyde)

10.  MODE OF ACTION AND APPICATION OF DISINFECTANT:
• Chemical agents are most commonly used as disinfectants. These
chemical agents are classified as follows:
1. Acid and alkalies
2. Halogens
3. Heavy metals
4. Phenols and its derivatives
5. Alcohol
6. Aldehydes
7. Dyes:
8. Quaternary ammonium compounds
9. Detergents and soaps.

11. 1. Acid
• Examples: acetic acid, citric acid Acidic disinfectants function by destroying
the bonds of nucleic acids and precipitating proteins. Acids also change
the pH of the environment making it detrimental to many microorganisms.
Concentrated solutions of acids can be caustic, cause chemical burns, and
can be toxic at high concentrations in the air. These characteristics limit their
use. The antimicrobial activity of acids is highly pH dependant. Acids have a
defined but limited use as disinfectants.

12. • Acetic acid is usually sold as glacial acetic acid (95% acetic acid)
which is then diluted with water to make a working solution
concentration of 5%. The concentrated form is corrosive to the skin
and lungs, but the typical dilution (5%) is considered non-toxic and
non-irritating. Acetic acid is typically applied by spraying, misting or
immersing an item in a diluted solution. Household vinegar is a 4-5%
solution of acetic acid (by volume). Acetic acid has poor activity in
organic material

13. 2. Alkalis
• Examples: sodium or ammonium hydroxide, sodium carbonate, calcium oxide Alkaline agents
work by saponifying lipids within the envelopes of microorganisms. The activity of alkali
compounds is slow but can be increased by raising the temperature. Alkalis have good
microbicide properties, but are very corrosive agents and personal protection precautions
should be observed.
• Sodium hydroxide (lye, caustic soda, soda ash) is a strong alkali used to disinfect buildings but
is highly caustic. Protective clothing, rubber gloves, and safety glasses should be worn when
mixing and applying the chemical. Lye should always be carefully added to water. Never pour
water into lye; a very violent reaction will occur as well as the production of high heat that can
melt plastic containers. Sodium hydroxide is corrosive for metals. It is considered an effective
FMD disinfectant.

14. • Ammonium hydroxide is an effective disinfectant against coccidial oocysts
however strong solutions emit intense and pungent fumes. This substance
is not considered effective against most bacteria. General disinfection
should follow the use of this compound.
• Sodium carbonate (soda ash, washing soda) has been used in a hot solution
(180o F) for disinfecting buildings, which have housed animals with FMD.
It is more effective as a cleanser than a disinfectant since it lacks efficacy
against some bacteria and most viruses. A 4% solution has been listed as an
approved chemical for the FMD virus. It has poor activity in the presence
of organic material and can be deactivated by hard water. It can be irritating
and requires protective clothing and is harmful to aquatic life.
• Calcium oxide (quicklime) becomes lime wash when mixed with water.
This has biocidal effects on some bacteria and virus and is sometimes
spread on the ground following depopulation of infected premises and has
also been used to retard putrefaction of buried carcasses after depopulation.
It is not very effective against the FMD virus.

15. 2. HALOGENS:
• Mode of action:
Oxidizing agents and cause damage by oxidation of essential sulfydryl groups of
enzymes.
Chlorine reacts with water to form hypochlorous acid, microbicidal.
• Examples:
Chlorine compounds (chlorine, bleach, hypochlorite) and iodine compounds (tincture
iodine, iodophores)
• Application:
i. Effective disinfectants and antiseptics
ii. Microbicidal
iii. Also sporicidal with longer exposure

16. 3. HEAVY METALS:
• Mode of action: Act by precipitation of proteins and oxidation of sulfydryl
groups They are bacteriostatic
• Examples:
Mercuric chloride, silver nitrate, copper sulfate, organic mercury salts (e.g.,
mercurochrome, merthiolate)
• Applications:
Silver compounds as antiseptics
Silver sulfadiazine for burns
Silver nitrate in eye infection
Merthiolate in 1:10000 -preservation of serum
Copper salts as a fungicide

17. 4.PHENOL:
• Mode of action:
Act by disruption of membranes, precipitation of proteins and inactivation
of enzymes
• Examples:
5% phenol, 1-5% Cresol, 5% Lysol, hexachlorophene, chlorhexidine,
chloroxylenol
• Applications:
i. As disinfectants at high concentration and as antiseptics at low
concentrations
ii. Bactericidal, fungicidal, but are inactive against spores and most viruses
iii.Effective in the presence of organic material and remain active on
surfaces long after application

18. 5. ALCOHOLS:
Mode of action:
Alcohols dehydrate cells, disrupt membranes and cause coagulation of protein
• Examples:
Ethyl alcohol, isopropyl alcohol and methyl alcohol
• Application:
i. 70% ethyl alcohol (spirit) is used as antiseptic on skin
ii. Isopropyl alcohol is preferred to ethanol •
iii. Also used to disinfect surfaces • Used to disinfect clinical thermometers •
iv. Methyl alcohol kills fungal spores, hence is useful in disinfecting inoculation hoods
• Disadvantages:
Skin irritant, volatile (evaporates rapidly), inflammable

19. 6.ALDEHYDES:
• Mode of action:
Acts through alkylation of amino-, carboxyl- or hydroxyl group, damages nucleic acids. It kills all
microorganisms, including spores
• Examples:
Formaldehyde, Glutaraldehyde
• Application:
i. Bactericidal, sporicidal, and also effective against viruses •
ii. Can also be used as chemical sterilants 40% Formaldehyde (formalin): for surface disinfection and
fumigation
iii. 10% formalin with 0.5% tetraborate sterilizes clean metal instruments 2% glutaraldehyde •
iv. To disinfect hospital and laboratory equipments •
v. An exposure of at least 3 hours at alkaline pH is required for action by glutaraldehyde •
vi. Especially effective against tubercle bacilli, fungi, and viruses

20. 7. Quaternary ammonium compound:
• Mode of actions:
Disruption of cell wall and membrane. They also inactive enzyme and denature protein.
• Examples:
• Cationic detergents are known as quaternary ammonium compounds (or quat) •
• Cetrimide and benzalkonium chloride act as cationic detergents
• Application:
• active against vegetative cells, Mycobacteria and enveloped viruses
• As disinfectants at dilution of 1-2% for domestic use and in hospitals.
• Used for control of microorganisms on floors, walls, nursing home and other public place

21. 8. DYES:
• Acridine dyes, Aniline dyes
• Act by interfering with the synthesis of nucleic acids and proteins in bacterial cells
• Acridine dyes such as acriflavin and aminacrine
• More effective against gram positive bacteria than gram negative bacteria and are more
bacteriostatic in action
• •Aniline dyes (such as gentian violent, crystal violet, and malachite green)
• •Also more active against Gram-positive bacteria than against Gramnegative organisms
• Applications:
i. Topically as antiseptics, on skin treat bacterial skin infections
ii. The dyes are used as selective agents in certain selective media

24. THANK YOU