2. DISINFECTION:
• Disinfection is a process that destroys
pathogenic organisms, but not
necessarily all microorganisms,
endospores, or prions.
• However, some disinfectants will kill
endospores with prolonged exposure
times.
3. An ideal disinfectant should
have following properties:
• Should have wide spectrum of activity.
• Active in the presence of organic matter
• Efficacy should not be lost on reasonable
dilution.
• Should not be expensive and must be
available easily.
4. • Should make effective contact.
• Should be active in any pH.
• Should be stable.
• Should have long shelf life.
• Should be speedy
• Should have high penetrating power
• Should be non-toxic, non-allergenic, non-
irritative or non-corrosive
• Should not have bad odour.
5. Factors affects disinfection
action:
■ Organism load
■ Nature of organisms
■ Concentration of chemical agents
■ Temperature
■ Organic matter
■ Duration of exposure
■ PH
■ Stability
■ Biofilm formation
6. GROWTH IN BIOFILMS
• It has been increasingly
recognized that many
infections are caused by
bacteria that do not
grow individually;
rather, they exist in
complex multicellular
communities in which
the microbes are sessile.
• Typically, microbial com-
munities form on
surfaces, hence “biofilm.”
Dental plaque bio
7. • Eventually this bacterial community surrounds
itself with a glycocalyx for environmental
protection. The glycocalyx also serves to keep
the biofilm community intact. Bacteria within a
biofilm produce small molecules, such as
homo-serine lactones, which are taken up by
adjacent bacteria and functionally serve as a
colony “telecommunication” system,
informing individual bacteria to turn on certain
genes at a particular time (Quorum Sensing).
These signals are known as quorum sensors.
8. For example:
• It is routine to debride our teeth every
day to remove the bacterial biofilm that
accumulates while we sleep.
• Similarly, biofilms are associated with
Streptococcus viridians on heart valves,
Pseudomonas aeruginosa lung
infections, Staphylococcus aureus on
catheters, or Legionella pneumophila
colonization of hospital water systems.
9. Choice of method
The choice of method of sterilization or
disinfection depends on:
• The nature of the item to be treated.
• The likely microbial contamination.
• The risk of transmitting infection to patients
or staff in contact with the item.
10. D value
• The decimal
reduction time
measures an agent’s
killing efficiency.
• It represents the time
needed to kill 90%
of the microbes
under specified
conditions
• Microbial death is
usually exponential.
13. MECHANISM OF ACTION OF
CHEMICAL AGENTS:
- By protein coagulation
- By disruption of the cell membrane resulting
in exposure, damage or loss of contents
- By removal of free sulphydryl groups
essential for the functioning of the enzymes
- By inhibit nucleic acid synthesis or alter
nucleic acid molecules.
- By causing oxidation or hydrolysis.
14. HIGH LEVEL DISINFECTANT:
• High level disinfectant: this is a chemical
that kills all microbial pathogens except
large number of spores.
• It may have some activity when used in
sufficient concentration and when the
contact time is increased.
Examples:
1. Aldehyde
2. Peracetic acid
3. Hydrogen peroxide
16. • They are sporicidal and can be used as
chemical sterilants.
• A 2% buffered solution of glutaraldehyde is
an effective disinfectant. It is less irritating
than formaldehyde and is used to disinfect
hospital and laboratory equipment.
• Glutaraldehyde usually disinfects objects
within about 10 -20 minutes but may require
as long as 10-14 hours to destroy all
endospores.
• Formaldehyde is usually dissolved in water
or alcohol before use.
17. ORTHO-PHTHALALDEHYDE
(0.55%):
- It has bactericidal activity.
- Also be used for semi critical items.
- It doesnot require activation.
- Better odour.
- Less irritation to eyes.
- Acts faster (5-10min).
- It does not kill spores effectively.
18. PERACETIC ACID:
• It is an oxidising agent.
• It has a good sterilisation effect on bacteria,
particularly common antibiotic resistant
bacteria such as METHICILLIN RESISTANT
STAPHYLOCOCCUS AUREUS,
VANCOMYCIN RESISTANT
ENTEROCOCCUS and CLOSTRIDIUM
DIFFICILE.
• It is one of the high level disinfectants
• The end products (acetic acid and oxygen) of
this agent are non toxic.
19. USES OF PERACETIC
ACID:
• It is used in automated
machines.
• Also available for manual
immersion ; 0.1%-0.2%,
used for 5-15 mins.
• Used to sterilize medical
,surgical, and dental
instruments.
• In combination with
hydrogen peroxide has been
used for disinfecting
hemodialyzers.
DISADVANTAGES OF
PERACETIC ACID:
- Expensive
- Has material
compatibility issues
- Causes chemical
irritation and eye
damage.
20. HYDROGEN PEROXIDE(H2O2):
• Has broad-spectrum activity against viruses,
bacteria, yeasts, and bacterial spores.
• It is effective against most organisms at
concentration of 3-6%
• 6-7% used as chemical sterilant in plasma
sterilization.
• It kills all organisms including spores at
higher concentration (10-15%).
21. MECHANISM OF ACTION OF
H2O2:
• By liberation of free hydroxyl radical on
decomposition of h2o2.
• These free radicals are the active
ingredient in the disinfection process.
• H2o2 can be degraded by catalase
producing organisms to water and
oxygen,
• This can be overcome by using higher
conc of h2o2.
22. DISADVANTAGES
OF H2O2:
- Expensive.
- Has material
compatibility issue(
contraindicated for use on
copper, brass, zinc,
aluminium).
- Can produce chemical
irritation and corneal
damage.
- It should be properly
stored in dark containers.
ADVANTAGES
OF H2O2:
- It is rapid in action
- Nontoxic.
- Has detergent
properties with
good cleaning
ability.
- Active in the
presence of
organic material.
24. ALCOHOL
• These agents effectively remove water from
biologic systems. Thus, they functionally act
as “liquid desiccants.”
• Alcohol, isopropyl alcohol, and n-propanol
exhibit rapid, broad-spectrum antimicrobial
activity against vegetative bacteria, viruses,
and fungi but are not sporicidal.
• Activity is optimal when they are diluted to a
concentration of 60–90% with water.
25. USES OF ETHYL ALCOHOL AND
ISOPROPYL ALCOHOL:
● Used mainly as skin antiseptics at a conc of
60%-90% in water.
● They rapidly kill bacteria including tubercle
bacilli but they have no sporicidal or virucidal
activity.
● However human immunodeficiency virus is
susceptible to 70% ethyl alcohol and 35%
isopropyl alcohol in the absence of organic
matter.
26. ● It is used for
disinfecting smaller
non critical
instruments such as
thermometer, (10-
15mins).
● Disinfection of small
medical items /
surfaces(rubber
stoppers of multiple
dose medication vials
or vaccine bottles and
hubs of the central line.
● Disinfection of non
critical surfaces:
laboratory bench,
medication preparation
areas.
● Disinfection of external
surfaces of equipments
such as stethoscopes,
ventilator, manual
ventilation bags,
ultrasound machines
ADVANTAGES:
27. DISADVANTAGES OF
ALCOHOL:
● Flammable and must be stored in a cool, well
ventilated area
● Evaporate rapidly making exposure time
difficult to achieve unless the items are
immersed.
● May damage tonometer tips and lenses.
● Inactivated by organic matter.
28. METHYL ALCOHOL:
● It is effective against fungal spores.
● Used for cleaning cabinets and incubators.
● Methyl alcohol vapour is toxic and
inflammable.
29. PHENOLICS:
● JosephLister, the father of antiseptic
surgery, first introduced use of Phenol
(carbolic acid) in surgery (1867).
● It is produced by distillation of coal tar
between temperature of 170°c and 270°c.
30. Mechanism of action :
● Bactericidal effect of phenols is due to their
capacity to cause cell membrane damage,
● Inactivation of membrane bound oxidases and
dehydrogenases leading to lysis and death of
the microorganism.
32. CRESOLS:
● Lysol is a solution of cresols in soap.
● Used for disinfecting environmental surfaces
(eg: bedside tables, bedrails, lab.surfaces)
● Non critical medical devices.
● Active against a wide range of organisms
● Not readily inactivated by the presence of
organic matter.
33. CHLORHEXIDINE:
• Savlon ( chlorhexidine and cetrimide) is
widely used in wound Dressing , preoperative
disinfection of skin .
• It is bactericidal at a high dilution.
• They are more active against gram positive
than gram negative bacteria.
• No action against tubercle bacilli or spores.
• Have very little activity against viruses.
• Have a good fungicidal activity.
34. CHLOROXLENOL:
• It is an active ingredient of Dettol.
• It is less toxic
• Less irritant
• Readily inactivated by presence of organic
matter.
• Inactive against pseudomonas.
35. HEXACHLOROPHANE:
• It is more active against gram positive than
gram negative bacteria.
• It is applied on skin as prophylaxis against
staphylococcal infections.
• It is bacteriostatic at very high dilutions.
• It is potentially toxic and should be used with
care.
36. DISADVANTAGES OF
PHENOLICS:
• Phenol is a protoplasmic poison, i.e., it kills
the cell by denaturing and precipitating
proteins.
• Therefore, it causes necrosis and sloughing of
tissues.
• The lethal dose is between 3 and 30 g, but
may be as little as 1 g in the pediatric age
group.
• If it is ingested in large amounts, the fatal
period is about 3–4 h.
37. The corroded areas
have dead white to
yellow (buffy-
white) appearance
(Fig. 1). Phenol-
induced buffy
white Tongue.
38. HALOGENS:
• Among the halogens, iodine and chlorine are
two commonly used disinfectants.
• These are bactericidal and are effective
against sporing bacteria and viruses.
39. CHLORINE:
• Chlorine and it’s compound hypochlorite have been
used as disinfectants over time.
• They are markedly bactericidal and virucidal.
MECHANISM OF ACTION:
• The disinfection action of all the chlorine
compounds is due to release of free chlorine.
• When hypochlorite are added to water , the
chlorine reacts with water to form hypochlorous
acid .
• This hypochlorous acid is strong oxidising agents
and effective disinfectant.
40. Preparations of chlorine:
• Chlorine occur as
1. Free chlorine
2. Hypochlorite – available in 2 preparations.
• Liquid form( sodium hypochlorite or
household bleach)Powder form ( calcium
hypochlorite or bleaching powder)
• Other forms : sodium dichloroisocyanurate (
NaDCC) available as tablet and chlorine
dioxide.
41. USES OF CHLORINE:
• Chlorine (free chlorine) used for disinfection
of municipal water supplies and swimming
pool water.
• Sodium hypochlorite or house hold bleach –
(5.25%-6.15%) = 50,000ppm of available
chlorine. Appropriate dilution by adding with
water, for disinfection of various Hospital
supplies. The contact time is about 10-20 min.
42. • Large blood spill: 0.5%( 1:10 dilution or 5000ppm)
is used.
• Small blood spill: 0.05%( 1:100 dilution or
500ppm) is used.
• Pre treatment of liquid waste before disposal: 1% (
1:5 dilution), 10000 ppm is used.
• Laundry items : 0.1% ( 1 in 50 dilution, 1000ppm )
is used.
• Surface disinfectant: 0.5% (1:10 dilution) or
5000ppm is used.
• Clostridium difficle ( diarrheal stool ) :
Hypochlorite is sporicidal only >0.5 % ( 5000ppm).
43. ADVANTAGES:
• Broad spectrum (
bactericidal, fungicidal,
virucidal and rapidly
sporicidal).
• Non flammable
• Low cost
• Widely available
• Even small quantities of
drinking water –
disinfected by
HALAZONE
(parasulfone
dichloramidobenzoic
acid) tablet.
DISADVANTAGES:
• Hypochlorite solution decays
rapidly
• Should be prepared daily
• Should not be used in the
presence of formaldehyde
because the reaction product is
found to be carcinogenic.
• Offensive Corrosive damages
fabrics.
• Two important pathogens are
not killed by chlorine [
cryptosporidium and
giardia].
44. IODINE:
It acts by disruption of protein
and nucleic acid.
TINCTURE OF IODINE
• 2% iodine in
potassium iodide.
• Used as a antiseptic for
wound cleaning,
• Can cause staining and
skin allergy.
IODOPHOR:
• Compound of iodine
with surface active
agents known as
iodophores.
• Non staining
• Free of skin toxicity
45. IODOPHOR:
As Antiseptic:
• 5% topical solution
and ointment – used for
wound cleaning.
• 7.5% - hand scrub.
• 10% - surgical skin
preparation.
• 1%- oral antiseptic (
mouth wash)
As Disinfectant:
• For medical equipment
• Hydrotherapy tanks
• Thermometers
46. LOW LEVEL
DISINFECTANTS:
• A chemical that kills only vegetative
bacteria,
• Fungi
• Lipid enveloped viruses.
• Examples of LLD : 1) Quaternary
ammonium compound. 2) Chlorhexidine
gluconate.
47. QUATERNARY AMMONIUM
COMPOUND(QAC):
Mechanism:
• Act by inactivation of
energy producing
enzymes,
• Denaturation of
essential cell proteins
• Disruption of cell
membrane.
• Benzyl ammonium
chloride is the most
popular QAC.
• But it doesn’t act in the
presence of hard water.
• Didecyl dimethyl
ammonium bromide –
newer generation –
remain active in hard
water and better
compatible .
48. CHLORHEXIDINE
GLUCONATE(CHG):
• It is a biguanide disinfectant, acts by
disruption of cytoplasmic membrane.
USES:
1. 0.5 % - handrub
2. 4% - handwash
3. 0.1-0.2% - mouthwash
4. 2% - skin disinfectant before surgery
5. 0.3% - antiseptic for wound cleaning
49. SALTS:
• Salts of heavy metals have toxic effects on
bacteria.
• The salts of copper, silver and mercury are
used as Disinfectant.
• They are protein coagulants and acts by
combining with sulphydryl groups of
bacterial proteins and other essential
intracellular compounds.
50. • MERTHIOLATE( SODIUM ETHYL
MERCURITHIOSALICYLATE) - used in a
dilution of 1: 10,000 - preservation of sera.
• THIOMERSAL , MERCUROCHROME
and PHENYL MERCURY NITRATE – less
toxic and used as mild antiseptic.
• They have marked bacteriostatic but limited
fungicidal action.
• COPPER SALTS – are used as fungicidal.
51. SURFACE ACTIVE AGENTS:
• Substance which alter energy relationship at
interfaces, producing a reduction of surface
tension are known as surface active agents or
surfactants.
• MECHANISM:
1. These acts on the phosphate groups of cell
membrane and also enter the cell.
2. Result in loss of membrane semipermeability
and the cell proteins are denatured.
53. ANIONIC
COMPOUNDS:
CATIONIC
COMPOUNDS:
AMPHOTERIC:
• Have strong
detergent
• Weak antimicrobial
properties.
• Active at acidic PH
• Effective against
Gram positive
organisms
• Ineffective against
Gram negative
species.
• It is most important
antibacterial agents.
• Bactericidal for wide
range of organisms,
gram positive species.
• No action on spores and
tubercle bacilli.
• Active against viruses
with lipid envelopes ( eg
: rabies virus)
• Less against non
enveloped viruses ( eg:
enteroviruses).
- Known as Tego
compounds
- Possess detergent
properties of anionic
and antimicrobial
activity of cationic
compounds.
- Active against wide
range of Gram positive
& gram negative
organisms and some
viruses.
- Active over wide range
of pH.
The common cationic
compound are acetyl
trimethyl ammonium
bromide ( cetavalon or
cetrimide) and
Presence of organic matter
reduces their activity.
54. ANIONICCOMPOUNDS:
Example:
• Common soap
• Soap prepared from coconut oil (
saturated fatty acid)- more effective
against Gram Negative bacilli
• From unsaturated fatty acid ( oleic acid) –
against Gram positive & Neisseria group
of organisms.
55. DYES:
• Two groups of dyes, Aniline and acridine are
used as skin and wound antiseptics.
• Both are bacteriostatic in high dilution but
low bactericidal action.
56. ANILINE DYES:
• Include crystal violet, Brilliant green and malachite
green.
• More active against gram positive than gram negative
bacteria.
• No activity against M.tuberculosis.
• Hence, the use of it in the LJ medium makes it selective
for isolation of tubercle bacilli.
• Non – toxic and non – irritant to the tissues.
• Inhibited by the presence of organic material such as pus.
• Interfere with the synthesis of peptidoglycan component
of the cell wall.
57. ACRIDINE DYES:
• Includes acriflavine , euflavine , proflavin
and aminacrine.
• Not as selective as the aniline dyes.
• Affected very little by the presence of organic
material.
• More active against gram positive than gram
negative bacteria.
• They interfere with the synthesis of nucleic
acids and proteins on bacterial cells.
58. ETHYLENE OXIDE:
• It is a colourless liquid with boiling point of
10.7°C
• It has sweet , ethereal smell.
Mechanism:
• Acts by alkylating the amino, carboxyl,
hydroxyl, and sulphydryl groups in protein
molecules within the microbes and spores.
• It also reacts with DNA and RNA.
60. • Pure ethylene oxide is explosive, it is usually supplied in a
10 to 20% concentration mixed with either CO2 or
dichlorodifluoromethane.
• The ethyleneoxide concentration,humidity,temperature &
exposure time influence the rate of sterilization.
• A clean object can be sterilized if treated for 5 to 8 hours
at 38°C or 3 to 4 hours at 54°C when the relative
humidity is maintained at 40 to 50% and the ethylene
oxide concentration at 700 mg/L.
• Because it is so toxic to humans, extensive aeration (8-
12)hrs of the sterilized materials is necessary to remove
residual ethylene oxide.
61. Uses:
• It is effective against all types of
microorganisms including viruses and spores.
• Highly penetrating gas and readily penetrates
some plastics.
• Especially used for sterilizing heat sensitive
equipment like heart lung machines,
respirators, suture materials, dental
equipment, books and clothing.
62. DISADVANTAGE OF
ETHYLENE OXIDE :
• Highly inflammable.
• Highly explosive at higher conc of >3%.
• By mixing it with inert gases such as carbon
dioxide or nitrogen makes it less explosive.
• It has a potential toxicity to human beings,
including mutagenicity and carcinogenicity.
63. Sterilization control:
• Spores of Bacillus atrophaeus is used as
biological indicator to check the effectiveness
of sterilization.
64. PLASMA STERILIZATION:
• Plasma refers to a gaseous state
consisting of ions, photons, free
electrons and free radicals (such
as O and OH).
• Plasma sterilizer is a special
device used to create the plasma
state.
• It has the following steps:
1. Vacuum
2. Chemical sterilant
3. Gas plasma
65.
66. • Chemical sterilant: hydrogen peroxide
(H2O2) solution from a cassette, which gets
vaporized in the sterilization chamber to a
concentration of 6 mg/L.
• The H2O2 vapor diffuses through the
chamber (50 minutes), exposes all surfaces of
the load to the sterilant.
• Low temperature is maintained 37-44°C
throughout the cycle.
67. • Gas plasma: In the next step, an electrical field is
applied to the chamber to create a gas plasma. H2O2
breaks into free radicals such as hydroxyl (OH–)
and hydroperoxyl (HO2) which initiate
microbicidal action, interact with essential cell
components (e.g. enzymes, nucleic acids).
Finally, the excess gas is removed. The by-products of the
cycle (e.g. water vapor, oxygen) are nontoxic and therefore,
there is no need of an additional aeration step.
68. • Cycle duration: It has a cycle time of 75 min. The
newer versions have shorter cycles of 52 min and
24 min
• Sterilization control: Spores of Bacillus
stearothermophilus is used as a biological
indicator to check the effectiveness of sterilization.
71. Uses of Plasma
Sterilizer
• sterilization of materials
and devices that cannot
tolerate high
temperature and
humidity of steam
sterilizer, such as some
plastics, electrical
devices, and corrosion-
susceptible metals such as
arthroscope, micro and
vascular instruments,
spine sets and
laparoscope
DISADVANTAGE/
PRECAUTION:
• Items should be dried
before loading
• Linen or paper or
cellulose or liquid
cannot be processed
• It may not penetrate
well, especially in
channels or devices
designed with long
lumens.
• It has a small chamber,
therefore cannot be used
for bulk items .
• High cost of equipment
and packing materials.
72. METHOS TO TEST EFFICACY OF
STERILANT/DISINFECTANT:
• Rideal and Walker test or Phenol coefficient test: It tests the
efficacy of a phenolic disinfectant to kill Salmonella Typhi, when
compared with that of phenol.
• Chick Martin test: It is a modification of Rideal and Walker test, in
which the disinfectant acts in the presence of organic matter (e.g.
dried yeast, feces, etc.) to simulate the natural conditions.
• Capacity (Kelsey-Sykes) test: It tests the capacity of a disinfectant to
retain its activity when the microbiological load keeps increasing. It is
used to test new disinfectants procured in hospitals to know which
dilutions are suitable for use.
• In-use (Kelsey-Maurer) test: It simulates real-time situation. It is
used to determine whether an in-use solution of disinfectant in
hospital is microbiologically contaminated.
73. CHEMICAL INDICATOR:
It is heat or chemical sensitive material which
undergo a color change if the proper
sterilization is achieved.
I.e) time, steam quality, and temperature.
Common types used are:
• Class 1- exposure indicator or external pack
control.
• Class 2- bowie dick test or equipment control.
• Class 4 and 5- Internal pack control indicator.
74. Class 1 "process" indicators,
showing (A) unused tape; (B),
tape from a load which was
exposed to a short, interrupted
cycle, and (C), tape showing
complete colour change. Self-
sealing bags typically come with
an external ink indicator system
(D).
75. Typical Bowie-Dick test used
in a pre-vacuum autoclave,
which has a "flat pack of
cards" configuration.
Bowie-Dick test, showing pass
(A) and fail (B) results. An even
colour change to black is caused
by steam penetration. The
presence of residual colour (in
this case, blue) in the centre of
the pack indicates persisting air
or volatile gaseous materials.
76. Class 4 chemical indicators. The topmost
indicator (A) is a control unused
indicator.
Subsequent indicators show the colour
change at 15 secs (B),
30 secs (C),
2 mins (D), and
3.5 mins (E), all at 134 o Celsius. The
bottom indicator (E) is a "pass". Note
how the colour develops gradually over
time when at the correct temperature.
77. Reference:
• Prescott's Microbiology Book by Christopher J.
Woolverton, Joanne Willey, and Linda Sherwood
• David Greenwood - Medical Microbiology
• Bailey & Scott’s Diagnostic Microbiology,
• Jawetz, Melnick & Adelberg’s Medical Microbiology.
• Essentials of Medical Microbiology. By Sastry Apurba S ·
• Ananthanarayan and Paniker’s Textbook of Microbiology
