This PPT has been made for SYBSc Microbiology students in University of Mumbai

1. SYBSc Microbiology
USMB303 (B) Unit II.
Physical and chemical
agents for Microbial
Control
Mr.R.M. Sagalgile

2. General Considerations in Microbial Control
Microbial control belong to the general category of decontamination
procedures.
Contaminants: microbes present at a given place and time that are
undesirable or unwanted.
Most decontamination methods employ either physical agents: heat or
radiation, or
Chemical agents : disinfectants and antiseptics.
This separation is convenient, even though the categories overlap in some
cases; for instance, radiation can cause damaging chemicals to form, and
chemicals can generate heat.

3. Relative Resistance of Microbial Forms
• Highest resistance
– Prions: proteinaceous infectious particles, bacterial
endospores, primarily from bacteria in the genera Bacillus and
Clostridium.
• Moderate resistance
– Protozoan cysts; some fungal sexual spores (zygospores); some
viruses. In general, naked viruses are more resistant than
enveloped forms.
• Least resistance
– Most bacterial vegetative cells; fungal spores (other than
zygospores) and hyphae; enveloped viruses; yeasts; and
protozoan trophozoites

4. Terminology
Sterilization [Latin sterilis, unable to produce offspring or barren]: The process
by which all living cells, viable spores, viruses, and viroids are either destroyed
or removed from an object or habitat.
Autoclave : An apparatus for sterilizing objects by the use of steam under
pressure.
Sterile : An object which is totally free of viable microorganisms, spores, and
other infectious agents.
Sterilant : When sterilization is achieved by a chemical agent, the chemical is
called a sterilant.
Disinfection : Disinfection is the killing, inhibition, or removal of
microorganisms that may cause disease. (The primary goal is to destroy potential
pathogens, but disinfection also substantially reduces the total microbial
population.)
Disinfectants : Disinfectants are agents, usually chemical, used to carry out
disinfection and are normally used only on inanimate objects

5.  Sanitization : The process in which , the microbial population is reduced
to levels that are considered safe by public health standards.
 Antisepsis [Greek anti, against, and sepsis, putrefaction]: The prevention
of infection or sepsis is called as antisepsis and it is accomplished with
antiseptics.
 A disinfectant or antiseptic can be particularly effective against a specific
group, in which case it may be called a bactericide, fungicide, algicide,
or viricide.
 Chemotherapy : The use of chemical agents to kill or inhibit microbial
growth in tissues.
 Tyndallization: The process of repeated heating and incubation of
liquids to destroy bacterial spores.
 Pasteurization : The process of heating milk and other liquids to destroy
microorganisms that can cause spoilage or disease.
 Plasmolysis: Plasmolysis is the contraction/rupturing of the protoplast of
a cell , when placed in hypertonic solution, due to water loss.
 Plasmoptysis : It is the rupture of the cell wall which causes the
protoplasm to burst.

7. • Death is a phenomenon that involves the permanent termination
of an organism’s vital processes.
What Is Microbial Death?
Signs of life in complex organisms such as animals are self-evident,
and death is made clear by loss of nervous function, respiration, or
heartbeat.
In contrast, death in microscopic organisms is hard to detect,
because they often reveal no conspicuous vital signs to begin with.
The permanent loss of reproductive capability, even under
optimum growth conditions, has become the accepted
microbiological definition of death.

8. Factors that affect death rate
(a) Length of exposure to the agent.
Over time, the number of viable organisms
remaining in the population decreases
logarithmically.
(b) Effect of the microbial load.

9. Factors that affect death rate
(c) Relative resistance of spores
versus vegetative forms.
(d) Action of the agent, whether
microbicidal or microbistatic.

10. Antimicrobial agents and their modes of action
An antimicrobial agent’s adverse effect on cells is
known as its mode ( or mechanism ) of action .

11. Methods of control

12. Methods of Physical Control
1 • Heat
2 • Cold
3 • Desiccation
4 • Osmotic Pressure
5 • Radiation
6 • Filtration

13. Heat
Either moist or dry heat may be applied
Effects of high temperatures
Denature proteins
Interfere with integrity of cytoplasmic
membrane and cell wall
Disrupt structure and function of nucleic acids
Thermal death point
Lowest temperature that kills all cells in broth
in 10 min
Thermal death time
Time to sterilize volume of liquid at set
temperature

14. Heat
Decimal reduction time (D) or D value :.
The time required to kill 90% of the microorganisms
or spores in a sample at a specified temperature
z value :
The z value is the increase in temperature required to
reduce D to 1/10 its value or to reduce it by one log
cycle when log D is plotted against temperature
F value :
 The F value is the time in minutes at a specific
temperature (usually 250°F or 121.1°C) needed to kill a
population of cells or spores.

15. Autoclaving
Applications :
Sterilization of aqueous solutions e.g. nutrient media
sterilization of surgical dressings, plastics and rubber fabrics
Occasionally, sterilization of Petri plates, pipettes, flasks etc.
Sterilization of metallic instruments. (Immediate drying is necessary
to protect instruments from corrosion)
Disadvantages :
pH may be changed due to loss of water
Oils cannot be sterilized by autoclave as they are hydrophobic in
nature

16. Autoclaving
Applications :
Sterilization of aqueous solutions e.g. nutrient media
sterilization of surgical dressings, plastics and rubber fabrics
Occasionally, sterilization of Petri plates, pipettes, flasks etc.
Sterilization of metallic instruments. (Immediate drying is necessary
to protect instruments from corrosion)
Disadvantages :
pH may be changed due to loss of water
Oils cannot be sterilized by autoclave as they are hydrophobic in
nature

17. Tyndallization
Tyndallization is a process dating from the nineteenth century
for sterilizing substances, usually food, named after its inventor,
scientist John Tyndall.
It is still occasionally used. Steam Arnold is an apparatus used for
Tyndallization.

18. Pasteurization
Pasteurization or pasteurisation is a process that kills microbes (mainly
bacteria) in food and drink, such as milk, juice, canned food, and others.
Many substances, such as milk, are treated with controlled heating at
temperatures well below boiling, a process known as pasteurization in
honor of its developer Louis Pasteur.
Pasteurization does not sterilize a beverage, but it does kill any pathogens
present and drastically slows spoilage by reducing the level of
nonpathogenic spoilage microorganisms.

19. Pasteurization Methods
i. Low Temperature holding method (LTH)/Batch method: Heating
of liquid at 62.8°C i.e 63 °C (145°F) for 30min.
ii. Flash pasteurization or High-Temperature Short-Time (HTST)
method : Large quantities of liquids / milk are now usually subjected
to flash pasteurization or high-temperature short-term (HTST)
pasteurization, which consists of quick heating to about 71.7°C i.e.72°C
(161°F) for 15 seconds, then rapid cooling.
iii. Ultra High-Temperature (UHT) method : The dairy industry also
sometimes uses ultrahigh-temperature (UHT) sterilization. Milk and
milk products are heated at 140 to 150°C for 1 to 3 seconds.

20. Pasteurization destructs:
Mycobacterium tuberculosis & Coxiella burnetti (causative agents of tuberculosis and
Q-fever respectively).
Applications:
It is used:
To prevent transmission of milk borne pathogens
To control non-spore forming pathogens (primary target)
To kill unwanted contaminants in beverages
Products that are commonly pasteurized:
Beer, Canned food, Dairy products, Eggs, Milk, Juices, Low alcoholic beverages,
Syrups, Vinegar, Water, Wines

21. ii. Dry Heat :
Many objects are best sterilized in the absence of water by
dry heat sterilization.
The temperature of dry heat ranges from 160oC to several
thousand degrees.
Microbes are mostly more resistant to dry heat than moist
heat.
Mode of Action:
Disruption of cell membrane
Co-aggulation and denaturation/inactivation of proteins,
ribosome & nucleic material
It oxidizes and dehydrates cells
Reduce cells to ash
Inactivates membranes

22. ii. Dry Heat :
Dry heat sterilization can be achieved by :
Use of Hot Air Oven
Incineration
Temperature Holding Time (in min.)
160°C 120
170°C 60
180°C 30
Advantages and Applications:
•Dry heat does not corrode glassware and metal instruments as
moist heat does.
•It can be used to sterilize powders, oils, and similar items.
•Most laboratories sterilize glass Petri dishes and pipettes with dry
heat.
Disadvantages :
•Dry heat sterilization is slow
•It is not suitable for heat sensitive materials like many plastic and
rubber items.

23. Cold
 Freezing or refrigeration
 Mode of Action :
• Freezing items at -20°C or lower stops microbial growth
because of the low temperature and the absence of liquid
water.
• Refrigeration greatly slows microbial growth and reproduction,
but does not halt it completely.
• Some microorganisms will be killed by ice crystal disruption of
cell membranes, but freezing does not destroy contaminating
microbes.

24. Applications :
•Freezing is a very good method for long-term storage of microbial
samples when carried out properly.
•Many laboratories have a low-temperature freezer for culture
storage at -30 or -70°C.
•In diary industry, milk is stored in cold room to be kept free of
microbes or contamination.
•Because frozen food can contain many microorganisms, it should
be prepared and consumed promptly after thawing in order to
avoid spoilage and pathogen growth.

25. Drying/desiccation
Drying/desiccation is the gradual withdrawal of water from cells by exposure to
room air, leading to metabolic inhibition.
Vegetative cells directly exposed to normal room air gradually become
dehydrated, or desiccated.
Mode of action :
It greatly reduces the amount of water available to support microbial growth.
Applications :
Effective in preservation.
Combination of freezing and drying i.e. lyophilization.
It is a common method of preserving microorganisms and other cells in a
viable state for many years.

26. Advantages:
More delicate pathogens such as Streptococcus pneumoniae, the spirochete of
syphilis, and Neisseria gonorrhoeae can die after a few hours of air-drying.
Many others are not killed and some are even preserved.
A valuable way to preserve foods
Disadvantages :
Endospores of Bacillus and Clostridium are viable for millions of years under
extremely arid conditions.
Staphylococci and streptococci in dried secretions, and the tubercle bacillus
surrounded by sputum, can remain viable in air and dust for lengthy periods.
Many viruses (especially non-enveloped) and fungal spores can also withstand
long periods of desiccation.

27. Radiation
Radiation is defined as any form of energy emitted from atomic
activities that travels at high velocity through matter or space.
They are classified as ionizing and non-ionizing radiations.
High energy radiations includes ionizing radiations like X-rays, g Rays,
Cathode rays and non-ionizing UV light.

28. Ionizing Radiations Non- Ionizing Radiations
Responsible for ionization of
atoms/molecules.
Radiations with shorter wavelengths have
more penetration power. Because it sterilizes
in the absence of heat, irradiation is a type of
cold sterilization.
UV ray’s wavelength ranges from
100nm-400nm. Most lethal from 240-
480nm, and peak is at 260nm. Mercury
vapour lamp is commonly used source of
UV light. Do not ionize atoms.
Mode of Action :
i. Disrupts atomic structure of molecule by
dislodging/ejecting electrons.
ii. Results into electrical imbalance &
formation of ions.
iii. Ionizing radiations ionizes DNA
molecules in microbes, thus induces
mutation and halts replication and protein
synthesis.
iv. Penetrates solids and liquids.
Mode of Action :
i. It acts on DNA molecules.
ii. Forms T=T dimmers, induces
mutation
iii. Results in poor transcription and
inactive proteins synthesis.
iv. Effect of UV light is not so much
dentrimental as compared to ionizing
radiations.

29. Ionizing Radiations Non- Ionizing Radiations
Applications :
1.Foods like, meat can be sterilized
2.Use for g Rays obtained from
60Co are used for sterilization of
medical products like drugs,
vaccines, harmones and tissues
like bone, cartilages, skin and heart
valves
Applications :
1.To control air borne
contaminants in hospitals,
operation theatres, food
preparation areas etc.
2.Use for purification of liquids
including milk, fruit juice, beer,
wine etc.
Limitations:
1.Alteration in food flavor after
exposure to radiations
2.High risk to Machine operator
Limitation:
1.UV rays can damage eyes and
are known to cause sun burns
and skin cancers in humans.

30. It’s a pressure exerted by salt/solute on the cell membrane.
The conditions like hypotonic, hypertonic or isotonic affects the cell
membrane’s integrity and may result into lysis of cells.
Mode of Action : Microorganisms in high concentrations of salts and
sugars undergo plasmolysis.
Application : In food preservation. Preparation of short term cultures in
saline
Advantages: Easy and convenient, cheaper, no skilled personnel required.
Disadvantages: Molds and yeasts are more capable than bacteria of
growing in materials with low moisture or high osmotic pressure.
OSMOTIC PRESSURE :

31. Filtration is an excellent way to reduce the microbial
population in solutions of heat-sensitive material, and
sometimes it can be used to sterilize solutions.
Rather than directly destroying contaminating
microorganisms, the filter simply removes them.
Filtration :
1.Depth filters: These consist of fibrous or granular materials
that have been bonded into a thick layer filled with twisting
channels of small diameter.

32. 2. Membrane filters:
They have replaced depth filters for many purposes.
These circular filters are porous membranes, a little over 0.1
mm thick, made of cellulose acetate, cellulose nitrate,
polycarbonate, polyvinylidene fluoride, or other synthetic
materials.

33. 3. High-Efficiency Particulate Air (HEPA) filters :
Laminar flow biological safety cabinets employing high-
efficiency particulate air (HEPA) filters, which remove 99.97% of
0.3mm particles, are one of the most important air filtration
systems.
These are made
up of cellulose
acetate and
available in various
sizes.

35. Thank you

36. Although objects are sometimes disinfected with
physical agents, chemicals are more often employed
in disinfection and antisepsis.

37. Chemical agents in Microbial Control
Choosing a Microbicidal chemical :
• rapid action in low concentrations,
• solubility in water or alcohol and long-term stability,
• broad-spectrum microbicidal action without being toxic to human
• and animal tissues,
• penetration of inanimate surfaces to sustain a cumulative or
• persistent action,
• resistance to becoming inactivated by organic matter,
• noncorrosive or non staining properties,
• sanitizing and deodorizing properties,
• affordability and ready availability, and
• non offensive odor

38. • Factors that affect the germicidal activity :
• (1) the numbers and kinds of microbes that are present
• (2) the kinds of materials that are being treated
• (3) the time of exposure required, and
• (4) the strength and mode of action of the agent.
• Other factors:
• Length of exposure
• Concentration of the Chemical Agent

39. Germicidal chemical compounds
• Halogens
• Phenolic compounds,
• Alcohols
• Hydrogen peroxide
• Aldehydes
• Gases
• Detergents and soaps
• Heavy metals
• Dyes
• Acids & alkalis
• Quaternary Ammonium compounds

40. Phenolics
• Phenol was the first widely used
antiseptic and disinfectant. In 1867
Joseph Lister employed it to reduce
the risk of infection during operations.
Today phenol and phenolics (phenol
derivatives) such as cresols, xylenols,
and orthophenylphenol are used as
disinfectants in laboratories and
hospitals. The commercial disinfectant
Lysol is made of a mixture of
phenolics.

41. • Mode of Action : Phenolics act by :
– Denaturing proteins and disrupting cell membranes
– Precipitating cellular proteins and inactivate enzymes
• Spectrum /Range of Action : Bactericidal, fungicidal,
virucidal but NOT sporicidal.
• Applications :
– It is used in many commercial antiseptic and disinfectant
preparations
– 2-5% phenolic solution are used to disinfect sputum,
urine and feces etc.
– Cresol like compounds are used to treat surgical devices
– Hexachlorophene is most popular antiseptic

42. • Advantages:
– Phenolics are tuberculocidal, effective in the presence
of organic material
– Remain active on surfaces long after application.
• Disadvantages:
– They do have a disagreeable/objectionable odor
– They can cause skin irritation, corrosive
– They exhibits carcinogenic effect.
– It may cause brain damage.

43. Alcohols
• Alcohols are among the most widely used disinfectants
and antiseptics.
• The two most popular alcohol germicides are ethanol
and isopropanol, usually used in about 70-80%
concentration.
• A 10 to 15 minute soaking is sufficient to disinfect
thermometers and small instruments.
• Denaturation requires H2O, which is why aqueous
preparations are better than pure.
• 70% is best ethanol concentration for control of
microbes.

44. • Mode of Action :
– Coagulation of proteins and dissolving membrane lipids
– Dehydration of cells
• Spectrum /Range of Action :
– They are bactericidal and fungicidal but not sporicidal;
some lipid-containing viruses are also destroyed.
• Applications :
– 70-90% alcohol, acts as germicide and used in clinical
labs.

45. • Advantages:
– Soluble in water, Good disinfecting ability
– Readily available
– Enhance the effectiveness of other antimicrobial chemicals,
in tinctures
– Leaves no residues behind
• Disadvantages:
– Alcohol is more volatile, irritating and inactivated by organic
matter.
– It does not inactivate viruses like polio, hepatitis.
– Not good for wound disinfection because proteins coagulate
and form a protective coat around bacteria.

46. Heavy Metals
• For many years the ions of heavy metals such as mercury,
silver, arsenic, zinc, and copper were used as germicides.
• More recently these have been superseded by other less
toxic and more effective germicides (many heavy metals
are more bacteriostatic than bactericidal).

47. • Mode of Action :
– Combine with proteins i.e.enzymes, often with their sulfhydryl
groups, and inactivate them.
– They may also precipitate cell proteins, resulting in cell damage.
– The heavy metals are effective in trace concentration, this effect
is called as oligodynamic action/power.
• Spectrum /Range of Action :
– Bactericidal, fungicidal, virucidal but NOT sporicidal.
• Advantages:
– Very large applications with potential activity
– They are stable
• Disadvantage:
– Metal solutions are toxic and may cause allergies

48. • Applications :
• Silver :
– A 1% solution of silver nitrate is often added to the eyes of infants to
prevent ophthalmic gonorrhea
– Silver sulfadiazine is used on burns.
• Mercury :
– Primarily bacteriostatic but broad range of activity.
– Mercuric chloride is one formulation that was once used to treat syphylis..
• Copper :
– Copper sulfate is used to control green algae growth in ponds, pools,
reservoirs and fish tanks and copper compounds are sometimes used in
paint to prevent mildew.
• Zinc:
– Zinc chloride is used in some mouthwashes, zinc pyrithione in antidandruff
shampoos.

49. Halogens
• A halogen is any of the five elements (fluorine,
chlorine, bromine, iodine, and astatine) in group
VIIA of the periodic table.
• They exist as diatomic molecules in the free state
and form salt like compounds with sodium and
most other metals.
• The halogens iodine and chlorine are important
antimicrobial agents.

50. • Mode of Action :
– Chlorine: The nascent oxygen is strong oxidizing agent and is
responsible for protein denaturation.
• Cl2 + H2O  HCl + HClO
• HClO  HCl + [O]
– Iodine : It interferes with intermolecular binding in
proteins. By oxidizing cell constituents and iodinating cell
proteins it kills the cells.
• Spectrum /Range of Action :
– Chlorine : Bactericidal, fungicidal, virucidal but NOT
sporicidal.
– Iodine : Bactericidal, fungicidal, virucidal and SPORICIDAL.

51. • Applications :
– Iodine is used as a skin antiseptic at higher concentrations, it may
even kill some spores.
– Iodine often has been applied as tincture of iodine, 2% or more
iodine in a water-ethanol solution of potassium iodide.
– Lugol's iodine solution is often used as
an antiseptic and disinfectant, for emergency disinfection of
drinking water.
– More recently iodine has been complexed with an organic carrier
to form an iodophor
– Chlorine is the usual disinfectant for municipal water supplies and
swimming pools

52. • Advantages:
– Soluble in water
– Good disinfecting ability etc
• Disadvantages :
– Although iodine is an effective antiseptic, the skin may be
damaged, a stain is left, and iodine allergies can result.
– An excess of chlorine is added to ensure microbial destruction.
– Chlorine reacts with organic compounds to form carcinogenic
trihalomethanes, which must be monitored in drinking water.
– Ozone sometimes has been used successfully as an alternative to
chlorination in Europe and Canada

53. Quaternary Ammonium Compounds/Quats
– Quats are cationic detergents attached to NH4
+.
• Mode of action :
– By disrupting plasma membranes, they allow cytoplasmic
constituents to leak out of the cell.
– Also denature proteins (inhibit enzymes) and are surface active.
• Spectrum /Range of Action :
– Bactericidal, fungicidal, algaecidal, virucidal, amoebicidal but NOT
sporicidal.

54. • Applications :
– In dilutions ranging from 1:100 to 1:1,000, quats are mixed with cleaning
agents to simultaneously disinfect and sanitize floors, furniture,
equipment surfaces, and restrooms.
– They are used to clean restaurant eating utensils, food-processing
equipment, dairy equipment, and clothing.
– They are common preservatives for ophthalmic solutions and cosmetics.
• Advantage :
– Used at medium concentrations
– They function best in alkaline solutions
• Disadvantage :
– Inactivated by anions, soaps, detergents, and organic material.
– They have only microbiostatic effects.
– The quats are ineffective against the tubercle bacillus, hepatitis virus,
Pseudomonas, and spores at any concentration.

55. Dyes
Dyes are important in staining techniques and as selective and
differential agents in media; they are also a primary source of
certain drugs used in chemotherapy. Dyes are classified as
reactive and non-reactive. Further they are grouped as :
acridine dyes (Benzoflavin, Crystal voilet etc), aniline dyes,
triphenymethane (bromocresol green, malachite green etc).

56. • Mode of Action :
– Interacts with bacterial nucleic acids. i.e. It intercalates between
base pairs in DNA
– Sometimes acts as analogues of biomolecules and interfere with
metabolism of microbial cells
• Spectrum /Range of Action :
– Bactericidal, fungicidal but NOT sporicidal.(Narrow spectrum)
• Advantage :
– It is believed that some dyes are less allergic and more stable
(Mehrabian et al., 2000).
• Disadvantages :
– Dyes will continue to have limited applications because they stain
– They have a narrow spectrum of activity.

57. • Applications :
– Aniline dyes : Crystal violet, brilliant green and also
malachite green are very active against gram-positive
species of bacteria and various fungi, they are
incorporated into solutions and ointments to treat skin
infections (ringworm).
– Acridine dyes: The yellow acridine dyes, acriflavine and
proflavine, are sometimes utilized for antisepsis to treat
mild burns and wound treatment in medical and veterinary
clinics.

58. Detergents
• [Latin detergere, to wipe off or away] are organic molecules that
serve as wetting agents and emulsifiers because they have both
polar hydrophilic and nonpolar hydrophobic ends.
• Detergents are complex organic substances that act as
surfactants.
• They carry either an anionic (negative) or cationic (positive)
charge.
• Most anionic (negatively charged) detergents have limited
microbicidal power. Soaps belong to this group.
• Cationic detergents are the most effective, especially the
quaternary ammonium compounds (usually shortened to quats).

59. • Mode of Action : They act as surfactants.
– Disruption of microbial membranes and may also
denature proteins.
– The loss of its selective permeability.
– Leakage of microbial cytoplasm, precipitate proteins,
and inhibit metabolism
• Spectrum /Range of Action :
– Bactericidal, fungicidal, algaecidal, virucidal,
amoebicidal but NOT sporicidal.

60. • Applications :
– Cationic detergents are often used as disinfectants for food
utensils and small instruments and as skin antiseptics.
Several brands are on the market. Zephiran contains
benzalkonium chloride (quats) and Ceepryn, cetyl
pyridinium chloride.
– Soaps destroy only highly sensitive forms such as the agents
of gonorrhea, meningitis, and syphilis.
– Soaps function primarily as cleansing agents and sanitizers
in industry and the home.
– Help to mechanically remove large amounts of surface soil,
greases, and other debris that contains microorganisms.

61. • Advantages :
– Stable, nontoxic, and bland
– Because of their ability to interact with surfaces, detergents
make good wetting agents, cleansing agents, and
emulsifiers.
– Soaps gain greater germicidal value when mixed with agents
such as chlorhexidine or iodine.
• Disadvantages:
– They may be inactivated by hard water and organic matter.
– Pseudomonas can metabolise cetrimide, using them as a
carbon, nitrogen and energy source.

62. Aldehydes
Both of the commonly used aldehydes are:
Formaldehyde and Glutaraldehyde,

63. • Mode of Action :
– They are highly reactive molecules.
– They combine with nucleic acids and proteins and
inactivate them, probably by cross linking and
alkylating molecules.
• Spectrum/Range of Action :
– They are bactericidal, fungicidal & SPORICIDAL
and can be used as chemical Sterilant.

64. • Applications :
– Formaldehyde : Formaldehyde is usually dissolved in water or
alcohol before use. 40% Formaldehyde (formalin) is used for
surface disinfection and fumigation of rooms, chambers,
operation theatres, biological safety cabinets, wards, sick
rooms etc.
– Fumigation is achieved by boiling formalin, heating
paraformaldehyde or treating formalin with potassium
permanganate.
– Glutaraldehyde : A 2% buffered solution of glutaraldehyde is
an effective disinfectant.

65. • Advantages:
– It can be used to treat large surface area (in hospital to
disinfect the working rooms, operation theatres etc)
– As it forms fumes, it may be readily dispersed in the
environment
• Disadvantages:
– Vapors are irritating (must be neutralized by ammonia),
– It has poor penetration,
– It leaves non-volatile residue,
– It’s activity is reduced in the presence of protein.
– Gluteraldehyde requires alkaline pH and only those articles
that are wettable can be sterilized.

66. Hydrogen Peroxide and Related Germicides
• Hydrogen peroxide (H2O2) is a colorless, caustic liquid that
decomposes in the presence of light, metals, or catalase into
water and oxygen gas.
• Peroxide solutions have been used for about 50 years.
• Early formulations were unstable and inhibited by organic
matter, but manufacturing methods now permit synthesis of
H2O2 so stable that even dilute solutions retain activity
through several months of storage.

67. • Mode of action :
– The germicidal effects of hydrogen peroxide are due to
the direct and indirect actions of oxygen.
– Oxygen forms hydroxyl free radicals (.OH), which, like
the superoxide radical, are highly toxic and reactive to
cells.
– Although most microbial cells produce catalase enzyme
to inactivate the metabolic hydrogen peroxide, it cannot
neutralize that amount of hydrogen peroxide which is
entering the cell during disinfection and antisepsis.
• Spectrum/Range of Action :
– Bactericidal, virucidal, and fungicidal and in higher
concentrations-Sporicidal.

68. • Applications :
– As an antiseptic, 3% hydrogen peroxide serves a variety of
needs, including skin and wound cleansing, bedsore care, and
mouth washing.
– It is especially useful in treating infections by anaerobic bacteria.
– It is also a versatile disinfectant for soft contact lenses, surgical
implants, plastic equipment, utensils, bedding, and room
interiors.
– Hydrogen peroxide solutions and vapors are the latest method
in flash sterilization of food packaging equipment and other
industrial processes.
• Another compound with effects similar to those of hydrogen
peroxide is ozone (O3), used to disinfect air, water, and industrial air
conditioners and cooling towers.

69. Sterilizing Gases
• Processing inanimate substances with chemical
vapors, gases, and aerosols provides a versatile
alternative to heat or liquid chemicals. Currently,
those vapors and aerosols having the broadest
applications are ethylene oxide (ETO), propylene
oxide, and betapropiolactone (BPL).

70. • Mode of Action:
Ethylene oxide Betapropiolactone
1. It is a very strong alkylating
agent.
2. It reacts vigorously with
functional groups of DNA and
proteins.
3. Through these actions, it
blocks both DNA replication
and enzymatic actions.
1. In the cells, it reacts readily
with organic compounds
containing available amino,
carboxyl, sulfhydryl, and
hydroxyl groups
2. It has somewhat similar action
like EtO.

71. • Spectrum/Range of Action :
Ethylene oxide Betapropiolactone
Bactericidal, fungicidal and
also Sporicidal
Bactericidal, virucidal,
fungicidal and also Sporicidal

72. • Applications :
– Ethylene oxide : Sterilization of disposable plastic petri
dishes and syringes, heart-lung machine components,
sutures, and catheters.
– Betapropiolactone : It is used to sterilize vaccines (to
inactivate viruses) and sera. The dilute solutions of
Betapropiolactone can be used to sterilize human
arterial homografts.
– It also used for disinfecting whole rooms and
instruments, sterilizing bones.

73. • Advantages :
Ethylene oxide Betapropiolactone
1. It rapidly penetrates packing
materials, even plastic wraps.
2. It is suitable for thermo labile
compounds
3. It does not damage moist
sensitive substances.
i. BPL decomposes to an
inactive form after several
hours and is therefore not as
difficult to eliminate as EtO.
ii. It also destroys
microorganisms more readily
than ethylene oxide.

74. Ethylene oxide Betapropiolactone
i. Long exposure is necessary
ii. Extensive aeration of the
sterilized materials is
necessary to remove
residual
iii.It is so toxic and expensive
i. It does not penetrate
materials well
ii. BPL has not been used as
extensively as EtO.
iii.It may be carcinogenic.
• Disdvantages :

75. Thank You