The document discusses various chemical agents used for disinfection. It describes the ideal properties of disinfectants and factors affecting their potency. Various classes of chemical disinfectants are explained - alcohols, aldehydes, dyes, halogens, phenols, gases, surface active agents and metallic salts. Specific chemicals from each class are mentioned along with their mechanisms and uses. Methods of testing disinfectants are also briefly covered.

1. Dr.V.S.Vatkar
Asso Prof
Microbiology Department
D Y Patil Medical College, Kolhapur
STEARILIZATION –II
CHEMICAL AGENTS

2. CHEMICAL AGENTS
(DISINFECTANTS)
 Definition: The process of destruction of
vegetative forms of pathogenic organisms is
known as Disinfection.
 Properties of disinfectant: Ideal
antiseptic/disinfectant
 Wide spectrum of activity (effective against all
microbes)
 Fast action & high penetration power
 Stable, non toxic, non irritant, safe & easy to use
 Be effective in acidic or alkaline medium
 Be active in presence of organic mater
 Compatible with other agents , cheap & easily

3. Factors which determines potency
of disinfectant
 Concentration
 Time of action (contact period)
 Nature of the organism
 pH of the medium
 Temperature
 Presence of extraneous material

4. Chemical agents
 Alcohols
 Aldehydes
 Dyes: aniline & acridine dyes
 Halogens: iodine, chlorine
 Phenols: carbolic acid
 Gases: ethylene oxide, formaldehyde, BPL,
H2O2 fogging
 Surface active agents
 Metallic salts

5. Mode of action of disinfectants
 Protein coagulation
 Disruption of cell membrane, causes
damage or loss of cell content
 Removal of free sulphydryl gr essential
for the functioning of the enz & life of cell
 Substrate competition: compound
resembles like a essential substrate of
enz which misleads the metabolism of
the cell

6. a) ALCOHOLS
 Commonly used: 70% isopropyl alcohol, methyl
alcohol, ethyl alcohol (ethanol)
 Have poor penetrating power : must not be used
in heavily soiled organic matter
 Mechanism of action:
 Destruction of bacterial cell proteins (denaturation
of bacterial proteins)
 No action on spores & viruses
 Action enhances in presence of water (70% alc –
more effective than 90% alc)

7. Uses:
 Skin antiseptics: ethyl alc & isopropyl alc
(60-90% conc in water)
 Isopropyl alc: preferred - better fat
solvent & has more bactericidal
capacity, disinfection of clinical
thermometers
 Fungal spores: methyl alc is effective
(toxic & inflammable)
 Incubators & cabinets are cleaned with
methyl alc

8. b) Aldehydes:active against amino gr in
protein mol
 Commonly used: formaldehyde, 2%
gluteraldehyde
 Formaldehyde: bactericidal & sporicidal, lethal
effects on viruses, used to preserve specimens,
formaldehyde gas used for sterilization of
instruments, fumigation of wards, OTs etc.
 gas is irritant & toxic
 Woolen blankets, wool & hide kills spores
including anthrax spores
 Anesthetic machine , baby incubators, lab
cabinets.
 40% formaldehyde is used for sterilization.
 Low penetrating power under dry condition &
increases in moist condition. Achieved by

9. 2% Gluteraldehyde:
 rapidly viricidal (HIV/ HBV),
Mycobacteria, fungi, less effective
against spores. Less toxic, less irritant,
less corrosive, no deleterious effect on
lenses of instruments
 CIDEX,CLINCIDE brand names
 Uses: cleaning lens instruments like
cystoscope, bronchoscope, ET tubes,
face masks, polythene tubing, also for
metal instruments etc
 Corrugated rubber tubes.

10. Orthophthalaldehyde
 Bactericidal activity
 Used to clean endoscopes between patients as it
is quick, effective and safe
 Peracetic acid:
 Good sterilization effect against multidrug
resistant bacteria like MRSA, VRE, & Cl .difficile
 Hypochlorus acid:
 Generated from reverse reaction of Na
hypochlorite & H2O2
 Effective against pathogenic bacteria, especiaaly
biofilm producers

11. c) Dyes
 Aniline dyes & Acridine dyes
 Mechanism of action: Aniline dyes kills the
bacteria by reaching with acid gr of the cell
 Acridine dyes: impairs DNA complex &
destroy the reproductive capacity of the cell.
 Uses:
 skin/wound antiseptics, selective agents in
media, more active against gram positive
organisms

12.  Aniline dyes: e.g. Crystal violet,
Malachite green, Brilliant green.
 More active against GP organisms than
GN organisms & no activity against
tubercle bacilli so Malachite green is
used in L-J medium
 Non irritant & non toxic to tissues

13. Acridine dyes:
 e.g. Acraflavine & Proflavin,
euflavin,
 If they impregnated in gauze , they
are slowly released in moist
environment.
 Mode of action: impair the DNA
complex of the organism & prevent
replication

14. d) Halogens- iodine &
chlorine
 Iodine : skin disinfectants (tincher iodine),
act against bacteria & viruses, not spores.
2.5% iodine solution : used in ophthalmia
neonaterum
 K iodide (2.5%) & ethanol combination more
effective
 Idophors: PVP (polyvinyl pyrolidone) or
ethoxylate non ionic detergent: free
microbicidal iodine is released from these
compounds
 Povidone iodine: not effective against
Pseudomonas aeruginosa & Bacillus cepecia.

15.  Chlorine: rapidly bactericidal
 Elemental chlorine (strong oxidizing agent),
hypochlorous acid (HOCl) & hypochlorite ions
(OCl -) are also used
 It is mainly used for purification of water ,
swimming pools, food etc.
 Hypochlorites: active against GP bact & GN
bact also viruses including HIV, HBV, less
effective against mycobacteria
 Non expensive, broad spectrum of activity
 Na Hypochlorite: house hold bleach
 Corrosive to metals, should not be mixed with
acids as it releases large amt of chlorine gas

16. Tincher iodine
Hypochlorite solution

17. e) Phenols: phenol, Lysol, cresol,
chorhexidine
 Bactericidal activity: effective against GP bact &
GN bact, less effective on spores & viruses
including HIV, HBV
 Readily absorb through skin & mucus memb, may
cause toxicity
 Lister (1865): father of antiseptic surgery first
used carbolic acid (phenol) for surgery as a
antiseptic solution & showed lower incidence of
post surgical inf
 Mechanism of action: 1) damages cell memb ,
causes cell lysis, 2) pptn of bacterial proteins
causes cell memb damage

18.  Phenol (carbolic acid): widely used disinfectant
in hospitals. Commonly used compounds are
Lysol & Cresol
 Cresol: used for sterilization of glass wears,
excreta, floor & OT cleaner
 Chloroxylenol: Dettol: used as a antiseptic , not
effective against GN bact
 Chorhexidine (Hibitane): effective against wide
range of bact including Ps.aeruginosa, less toxic,
skin antiseptic & wound dressing
 Uses: burns, wounds, surgical instruments, pre-
op disinfectant.

19. phenol lysol
Dettol

20. f) Gases: Ethylene oxide, BPL ,
formaldehyde
 Ethylene oxide gas: colourless liquid with B P
10.7 oC & normal temp & pressure is highly
penetrating gas with sweet ethereal smell. Irritant.
 Highly inflammable & explosive: if it is mixed with
CO2 or N2 its explosive tendencies decreases.
 It removes sulphydryl gr , amino gr, hydroxyl gr,
and carboxyl gr from bact cell (protein mol),
reacts with DNA & RNA causes impairment
 Mutagenic & carcinogenic
 Effective against all type of microorganisms
including viruses & spores.

21. Uses:
 Sterilization of
 heart-lung machines
 respirators
 Sutures materials
 Dental equipment
 Clothing
 Glass wear, metal, plastics, soil, some
food, tobacco etc
 Unsuitable for fumigation of rooms-
explosive property

22. Formaldehyde gas
 Widely employed for fumigation of OT & other
rooms
 Gas is generated by adding 150 gm of
KMnO4 to 280 ml of formalin for every 1000
cu.ft. of room volume
 Reaction generates considerable heat &
formaldehyde vapors are generated
 The doors & windows should be closed before
fumigation & remain unopened for next 48 hrs

23. Betapropiolactone gas
 Condensation product of ketane &
formaldehyde
 Low penetrating power, but efficient
fumigator
 Used for sterilization of biological
products
 Kills all organisms including viruses
 Carcinogenic

24. Low temperature steam (sterilizer)
formaldehyde
(LTSF)
 Steam at sub atmospheric pressure kills
spores of thermophilic bacilli (Bacillus
stearothermophilus)
 Saturated steam under pressure of 263
mm Hg , temp 73o C
 Hydrogen Peroxide fogging (H2O2):
 Bactericidal
 Oxidizes the cell wall of the organism

25. Oxidizing agent:
H2O2 (hydrogen peroxide)
 Kills all micro organisms including
spores at higher conc, fugicidal, viricidal,
mycobactericidal
 Uses: plastic implants, contact lenses,
surgical prostheses
 Gas is created in a special chamber/ in
fogging machine
 Process is not effective below 42oC
 Advantages: short cycle time & non toxic

26. g) Surface active agents
 Reduces surface tension : detergents ,
emulsifiers
 Classified into 4 grs : anionic, cationic, non-ionic
& amphoteric
 Mechanism of action: act on phosphate gr of
cell memb & enter into the cell. Memb looses its
semi-permeability & proteins are denatured
 Cationic compounds : quaternary ammonium
compounds : bactericidal, mostly against GP bact
than GN bact. No action on spores, mycobacteria
 Cetavlon /Cetrimide: acetyl trimethyl ammonium
bromide

27.  Anionic disinfectants: Soaps
 Prepared from saturated fatty acids : coconut oil:
effective against GNB
 Prepared from unsaturated fatty acids: oleic acid:
effective against GP bact & Neisseria gr of
organisms
 Amphoteric compounds: Tego compounds, not in
general use

28. Metallic salts
 Germicidal action depends on their conc, salt of
heavy metals have greater action
 Salts of silver, copper & mercury are used as a
disinfectants
 They causes coagulation of bacterial protein by
combining with sulphydryl gr of bacterial cell
 Mercuric chloride : highly toxic
 Organic compounds: thiomersal, phenyl mercury
nitrate, mercurochrome: less toxic : mild
antiseptics
 1% silver nitrate (AgNO3) used for burns &
gonoccocal conjunctivitis in newborn
 Copper : marked fungicidal

29. Plasma sterilizers
 Plasma : known as fourth state of
matter, consist of ions, electrons &
neutral particals
 Radio friquency energy is applied to
create electromagnetic field, into this
H2O2 fumes are introduced
 Generating free radicals of H2 & O2
 Sterilizes the articles.

30. PLASMA STERILIZER

31. Testing of disinfectants
 Rideal Walkar Test: suspension
containing equal no of typhid bacilli are
submitted to varying conc of phenol.
 Chick Martin Test : 3% dried yeast or
human faeces suspension in water is
tested with disinfectant