1. Chemical Methods ofChemical Methods of
DisinfectionDisinfection
Fe A. Bartolome, MD, FPASMAP
Department of Microbiology
Our Lady of Fatima University

2. SterilizationSterilization
• Killing of all microorganisms,
including bacterial spores
DisinfectionDisinfection
• Reducing the number of bacteriaReducing the number of bacteria
to a level low enough that diseaseto a level low enough that disease
is unlikely to occuris unlikely to occur
• Some organisms and bacterialSome organisms and bacterial
spores may survivespores may survive

3. AntisepticsAntiseptics
• Chemicals used to kill micro-
organisms on the surface of skin
and mucous membranes

4. • Differ from systemically-active anti-
microbials in that they possess little
selective toxicity  toxic not only for
microbial pathogens but for host cells
as well
• Can be used only to inactivate
microorganisms in the inanimate
environment or, to a limited extent, on
skin surfaces  cannot be administered
systemically

5. Factors that affect efficacy of a chemical agent:Factors that affect efficacy of a chemical agent:
1. Concentration of chemical agent
• Higher concentration bactericidal EXCEPT
alcohol (50% - 80%)
2. Time
• Longer time of exposure, better killing action
3. Temperature
• High temperature speeds up rate of chemical
reaction
4. Nature of surrounding medium
• pH of medium; presence of extraneous
materials like pus or blood
5. Nature of the organism
• Ability to produce spores; number & size of
inoculum

6. Characteristics of a good chemical disinfectant orCharacteristics of a good chemical disinfectant or
antiseptic:antiseptic:
1. Able to destroy a wide variety of microorganisms
2. Fast-acting  short contact time
3. Not affected by the presence of other substances
such as organic matter
4. Non-toxic to human tissues as well as non-
corrosive and non-destructive to materials for
which it is used
5. Should leave a residual antimicrobial film on the
treated surface
6. Water-soluble and easy to apply
7. Inexpensive and easy to prepare
8. Stable under storage and shipping conditions
9. Odorless

7. Damage Cell MembraneDamage Cell Membrane
A.A.Surface active agents – interact with theSurface active agents – interact with the
lipid in the cell membranelipid in the cell membrane  disrupt celldisrupt cell
membranemembrane
1. Cationic agents
• Quarternary ammonium compounds
• Cationic detergents widely used for
skin antisepsis
• Effective at alkaline pH
• Example: zephiran, benzalkonium
chloride

8. Damage Cell MembraneDamage Cell Membrane
A.A.Surface active agentsSurface active agents
2. Anionic agents
• Remove dirt through the process of
emulsification
• Effective at acidic pH
• Example: soaps and detergents
 Composed of long-chain, lipid-
soluble, hydrophobic portion and
a polar hydrophilic portion

9. Damage Cell MembraneDamage Cell Membrane
B.B.Phenolic compounds – also denature proteinsPhenolic compounds – also denature proteins
1. Phenol
• No longer used due to toxicity
• Mainly used as gold standard in the
evaluation of new chemical agents
using the phenol coefficient test
 Ratio of the concentration of phenol
to the concentration of the agent
required to cause the same amount
of killing under standard conditions
of the test

10. Damage Cell MembraneDamage Cell Membrane
B.B.Phenolic compoundsPhenolic compounds
2. Cresols (Methylphenol)
• Phenol derivatives
• More potent and safer
• Example: lysol
3. Hexachlorophene
• Biphenol with six chlorine atoms
• Used in germicidal soaps
• With possible neurotoxicity

11. Damage Cell MembraneDamage Cell Membrane
C.C.Alcohols – also denatures proteinsAlcohols – also denatures proteins
1. Ethanol
• Bactericidal
• Remove lipid from skin surface
• Widely used to clean the skin
before immunization or
venipuncture
• Requires presence of water for
maximal activity  more effective
at 70%

12. Damage Cell MembraneDamage Cell Membrane
C.C.Alcohols – also denatures proteinsAlcohols – also denatures proteins
2. Isopropyl alcohol
• Greater bactericidal activity than
ethanol; less volatile
• Side effect: narcosis due to inhalation
of fumes
2. Benzyl alcohol – used as preservative

13. Denaturation of Cellular ProteinsDenaturation of Cellular Proteins
1. Acids and alkali
• Strong acids and alkali – bactericidal
• Mycobacteria – resistant to 2% NaOH
(used in clinical laboratory to liquefy
sputum prior to culture)
• Weak acids (benzoic, propionic, and
citric acids) – used as food
preservatives
2. Alcohol and acetone
3. Phenol and cresol

14. Modify Functional Groups of Proteins andModify Functional Groups of Proteins and
Nucleic acids:Nucleic acids:
A.A.Heavy Metals – damage enzyme activity ofHeavy Metals – damage enzyme activity of
bacteria by binding to sulfhydryl groupsbacteria by binding to sulfhydryl groups
1. Mercurials
• Example: thimesoral (merthiolate) &
merbromin (mercurochrome)  skin
antiseptics
2. Silver compounds
• Bactericidal
• 1% silver nitrate – ophthalmia
neonatorum (Crede’s prophylaxis)
• Silver sulfadiazine – burn wounds

15. Modify Functional Groups of Proteins and NucleicModify Functional Groups of Proteins and Nucleic
acids:acids:
B.B.Halogens – oxidizing agentsHalogens – oxidizing agents  inactivateinactivate
enzymesenzymes
1. Iodine
• Inactivates sulfhydryl-containing
enzymes
• Also binds specifically to tyrosine
residues in proteins
• Best antiseptic sporicidal, bactericidal,
fungicidal, viricidal, amoebicidal
• Used prior to obtaining a blood culture
and installing IV catheters

16. Modify Functional Groups of Proteins and NucleicModify Functional Groups of Proteins and Nucleic
acids:acids:
B.B.Halogens – oxidizing agentsHalogens – oxidizing agents  inactivateinactivate
enzymesenzymes
1. Iodine
• Two forms:
a) Tincture of iodine
 2% iodine solution + potassium
iodide in ethanol
 Used to prepare skin prior to
blood culture
a) Iodophors
 Complexes of iodine with
detergents (e.g. Betadine)
 Used to prepare skin prior to
surgery; less irritating

17. Modify Functional Groups of Proteins and NucleicModify Functional Groups of Proteins and Nucleic
acids:acids:
B.B.Halogens – oxidizing agentsHalogens – oxidizing agents  inactivate enzymesinactivate enzymes
2. Chlorine
• Kills by cross-linking essential sulfhydryl
groups in enzymes  form inactive
disulfide
• For water treatment
• Hypochlorite (HOCl) – sanitize dairy &
food processing equipment; household
disinfectant

18. Modify Functional Groups of Proteins and NucleicModify Functional Groups of Proteins and Nucleic
acids:acids:
B.B.Halogens – oxidizing agentsHalogens – oxidizing agents  inactivateinactivate
enzymesenzymes
3. Hydrogen peroxide (H2O2)
• Wound cleansing; surgical devices and
soft plastic contact lenses
• Effectiveness limited by the organism’s
ability to produce catalase
• Attacks sulfhydryl groups

19. Modify Functional Groups of Proteins andModify Functional Groups of Proteins and
Nucleic acids:Nucleic acids:
C.C.Alkylating agentsAlkylating agents
1. Formaldehyde
• Sporicidal
• Commercially available as formalin (37%
solution in water)
• Hydroxymethyl group of formaldehyde
causes alkylation of –NH2 and –OH groups
of nucleic acids
• For preservation of specimens and
preparation of vaccines
• Kill Mycobacterium tuberculosis in sputum
and fungi in athlete’s foot

20. Modify Functional Groups of Proteins andModify Functional Groups of Proteins and
Nucleic acids:Nucleic acids:
C.C.Alkylating agentsAlkylating agents
2. Glutaraldehyde
• Sporicidal; with two reactive aldehyde
groups
• 10X more effective than formaldehyde
• Used as cold sterilant
• Medical equipments like respiratory
therapy machines and other equipment
that can be damaged by heat

21. Modify Functional Groups of Proteins andModify Functional Groups of Proteins and
Nucleic acids:Nucleic acids:
C.C.Alkylating agentsAlkylating agents
3. Ethylene oxide
• Sporicidal
• Hydroxyethyl group attacks the reactive
hydrogen atoms on essential amino acids
and hydroxyl groups
• Used in gaseous sterilization of heat-
sensitive materials or equipments like
heart-lung machine and polyethylene
tubes in anesthesia machines
• Potentially carcinogenic