This document discusses various chemical sterilization methods. It describes different classes of chemicals used for sterilization like alcohols, aldehydes, dyes, halogens, phenols, gases, and their mechanisms of action. Some commonly used chemicals are ethanol, formaldehyde, glutaraldehyde, iodine, chlorine, hydrogen peroxide. Ethylene oxide and formaldehyde gas are used for fumigation. The factors affecting potency of disinfectants like concentration, time, temperature are also mentioned.

1. STERILIZATION : CHEMICAL METHOD
Mr. Naresh Pokhrel
M.Sc Clinical Microbiology
Department of Microbiology
Father Muller Medical College, Mangalore

2. CHEMICAL METHODSCHEMICAL METHODS
 Alcohols
 Aldehydes
 Dyes
 Halogens
 Phenols
 Gases
-- Ethylene Oxide
- Formaldehyde gas
- Betapropiolactone (BPL)
 Surface active agents

3. Properties of an ideal disinfectant or
antiseptic
 Should have wide spectrum of activity and be
effective against all microorganism.
 Be active in presence of organic matter.
 Have speedy action.
 Have high penetrating power.
 Stable and non corrosive
 Cheap, easy to use
 Be effective in acid as well as alkaline media
 Be compatible with other antiseptics and
disinfectants
 Not cause local irritation or sensitization

4. THE FACTORS THAT
DETERMINE THE POTENCY OF
DISINFECTANTS ARE:
 Concentration of the substance ,
 Time of action,
 pH of the medium ,
 Temperature
 Nature of organism
 Presence of extraneous material

5. CHEMICAL AGENTS ACT IN VARIOUS
WAYS :
 Protein coagulation ,
 Disruption of cell membrane resulting exposure,
damage or loss of the contents
 Removal of free sulphydryl groups essential for the
functioning of the enzymes and
 Substrate competition- a compound resembling the
essential substrate of the enzyme diverts or
misleads the enzymes necessary for the
metabolism of the cell and cause cell death.

6. ALCOHOLSALCOHOLS
 Ethanol, methanol, isopropyl alcohol are frequently
used.
 Act by denaturing proteins.
 They have no action on spores.
 To be effective working concentration is 70-80 % in
water..
 Protein Slow its action whereas 1 % mineral acid and
alkali enhances it.

7. CONTD……
 Methyl alcohol is effective against fungal spores.
 Evaporate, leaving no residue
 The inside of the Chambers are wiped with liberal
amounts of methanol.
 A pad moistened with methanol and a dish of
water(to ensure high humidity) are kept inside ,
 And the incubator is left at working temperature
for several hours.

8. CONTD……..
 Uses: To disinfect skin prior to injections.
 Methyl alcohol is used to clean incubators and
biosafety cabinets
 Isopropyl alcohol is preferred as it is better fat
solvent, more bactericidal and less volatile
 Mainly used for disinfection of clinical thermometer.

9. ALDEHYDESALDEHYDES::
 Mechanism: active against the amino group in the
protein molecule.
 bactericidal, sporicidial and virucidal
 Commonly used aldehydes are Formaldehyde,
glutaraldehyde

10. FORMALDEHYDE GAS
 Excellent disinfectant
 Formalin(10%) was used extensively to preserve
biological specimens and for destroying anthrax
spores in hair and wool.
 Irritates mucous membranes, strong odour.
 10 % formalin containing 0.5 % sodium tetra borate
in water is used to sterilise clean metal instruments
 Formaldehyde in gaseous form is used to fumigate
sick rooms, operation theaters, labs

11. Glutaraldehyde:
 Less irritating and more effective than
formaldehyde.
 sterilizing agent : 2% solution of glutaraldehyde
(Cidex) which is Bactericidal, tuberculocidal,
virucidal in 10 minutes.
 Sporicidal in 3 to 10 hours

12. CONTD……….
 Commonly used to disinfect hospital instruments-
cystoscopes, endoscopes, corrugated rubber tubes,
face masks, metal instruments, polythene tubes

13. ORTHOPHTALALDEHYDE
 Has bactericidal activity
 Uses to Clean endoscopes between as it is
quick, effective and safe.

14. DYES
 ANILINE DYES -Brilliant green, malachite green
and crystal violet
 More active against gram+ve than gram-ve bacteria
 No activity against tubercle bacilli hence Malachite
green is used in Lowenstein Jensen media
 Non irritant, Non toxic
 These dyes are used in the microbiology laboratory
as selective agents in culture media.
 Lethal effects on bacteria are believed to be due to
their reaction with the acid group in the cell.

15. ACRIDINE DYES
 Are not selective as the aniline dyes.
 Proflavine, acriflavine, euflavine, aminacrine
 Impair DNA complexes of organisms and destroy
reproductive capacity of the cell

16. HALOGENS
Iodine:
 Tincture of iodine (alcohol solution) was one of
first antiseptics used.
 Combines with amino acid tyrosine in proteins and
denatures proteins.
 Stains skin and clothes
 bactericidal, virucidal and fairly active against
spores

17. Iodophors:
 Iodine compounds with non ionic wetting or surface
active agents
 It inhibits protein synthesis and oxidizes –SH groups
of amino acids
 Used as skin antiseptic in surgery.

18. CHLORINE
 When mixed in water forms hypochlorous acid:
 Cl2 + H2O ------> H+ + Cl- + HOCl
 Sodium hypochlorite (NaOCl)- Is active ingredient of
bleach
 Chlorine is easily inactivated by organic materials.
 The organic chloramines are used as antiseptics for
dressing wounds.

19. CONTD…….
 Not much useful against spores
 Used to disinfect drinking water, pools, and sewage
 For household use (bleach) it is used in conc. of
0.2-1%.

20. SURFACE ACTIVE AGENTS
 Alter energy relationship at interfaces producing a reduction of
interfacial tension
 Effective against gram positive bacteria
 Also destroy fungi, amoebas, and enveloped viruses

21.  Anionic compounds: Common soap and detergents
 Cationic compounds: Cetrimide and bezalkonium
chloride- used as antiseptics.
 Advantages: Strong antimicrobial action, colorless,
odorless, tasteless, stable, and nontoxic.
 Disadvantages: Form foam. Organic matter
interferes with effectiveness

22. OXIDIZING AGENTS
 Hydrogen peroxide and peracetic acid.
 H2O2 kills most organisms at 3-6% conc.
 At 10-25% kills even spores
 Used to disinfect plastic implants, contact lenses
and surgical prosthesis

23. Peracetic Acid:
 Has good sterilization effect on
bacteria,particulary common antibiotic
resistant bacteria such as methicilin
resistant Staphylococcus aureus,
vancomycin resistant Enterococcus and
Clostridium defficile

24. Ozone:
 Highly reactive form of oxygen
 Used along with chlorine to disinfect water
 More effective killing agent than chlorine
 Less stable and more expensive

25. PHENOLS AND PHENOLICS
 Phenol (carbolic acid) was first used by Lister as a
disinfectant.
 Obtained by distillation of coal tar between temp
170-270 0
C
 Active against gram+ve and –ve bacteria,
mycobacteria
 Little activity against spores and viruses

26.  Act by causing cell membrane damage, releasing
cell contents and causing lysis
 Resistant to inactivation by organic matter
 2% phenol is used to disinfect surfaces, floors,
tables etc

27. PHENOLICS
 Are chemical derivatives of phenol
 Cresols: Derived from coal tar (Lysol)
 LYSOL is used to disinfect linen- 3% lysol
 Advantages: Stable, persist for long times after
applied, and remain active in the presence of
organic compounds

28.  Related products chlorophenols and
chloroxyphenols are less toxic, less irritant but
inactive against pseudomonas
 Chlorhexidine is a nontoxic skin antiseptic- most
active against gram+ve and fairly against gram-ve
ones

29. HEAVY METALS
A. Silver
 1% silver nitrate used to protect infants against
gonorrheal eye infections
 B. Mercury
 Organic mercury compounds like merthiolate and
mercurochrome are used to disinfect skin wounds.
 C. Copper
 Bactericidal
 Fungicidal

30. GASES
 ETHYLENE OXIDE :
 Colourless liquid
 Boiling point 10.70
C
 At normal temp and pressure, it is a highly
penetrating gas with ethereal smell
 Acts by alkylating the amino, carboxyl, hydroxyl
and sulphydryl groups in protein molecule and also
by damaging DNA and RNA

31.  Highly inflammable
 Highly explosive at a concentration of >3% in air
 Carcinogenic and mutagenic
 Explosive tendency eliminated by mixing with inert
gases like CO2 and N2 to a concentration of 10%
 Sterilizing property

32.  USES : heat and moisture sensitive articles like
plastic and rubber articles, blankets,
pharmaceutical products, sutures, heart lung
machines, ventilators, catheters

33.  Objects to be sterilized are put in a cabinet from
which air has been removed using vacuum, and a
non explosive mixture containing ETO gas is
introduced to a pressure of 5-30 lb/in2
above atm
pressure,temp to be maintained at 45-55 0
C and
relative humidity 20-40%

34.  ETO GAS TEST ORGANISM : Bacillus subtilis
var.globigii
 A long period of aeration (to remove all traces of the
gas) is required before the equipment can be
distributed.
 The operating cycle ranges from 2-24 hours
 It is a relatively expensive

35. FORMALDEHYDE GASFORMALDEHYDE GAS
 Used to fumigate sick rooms, OT etc
 FORMALDEHYDE FUMIGATION:
 1) Electric boiler fumigation method
 2) Addition of formalin to potassium
permanganate (150 gm of potassium permanganate
to 280ml of formalin per 1000 cu.ft. of the room)


36. PROCEDURE:
 Close all doors & windows air tight and switch off
fans and A.C.
 Heat formalin solution till boiling
 Leave the OT unentered over night
 Enter the OT next day morning with
ammonia( 250ml/litre of formaldehyde)
 Keep the ammonia solution for 2-3 hrs to neutralize
formalin vapours

37. Betapropriolactone (BPL):
 More efficient than formaldehyde for fumigation
 carcinogenic

39. CONTD………