The document discusses antimicrobial methods for controlling microbial growth, highlighting the differences between sterilization, disinfection, antiseptics, and disinfectants. It describes various chemical agents and physical methods, including their mechanisms of action, effectiveness, and specific applications for controlling bacteria, fungi, and viruses. Additionally, it defines key terms related to antimicrobial agents and summarizes the factors influencing their efficacy.

1. The control of
microbial growth
Antimicrobial methods
and Chemotherapy
For B.Sc Optometry Students

2. Heard of Spores?
Bacterial spores are highly resistant, dormant
structures (i.e. no metabolic activity) formed in
response to adverse environmental conditions.
They help in the survival of the organisms during
adverse environmental conditions; they do not
have a role in reproduction.

3. Two different meaning..!
Sterilization is the killing or removal of all
microorganisms in a material or on an object.
Disinfection is the reduction of the number of
pathogenic microorganisms to the point where
they pose no danger of disease.

4. Two different meaning..!
Disinfectants are typically applied to
non living objects Eg: Dettol, Iodol
antiseptics are applied
to living tissue. Eg: ethanol, propanol,
Boric acid, H2O2

5. An antimicrobial is an agent that
kills microorganisms or stops their growth
Can be chemical or physical agents
What are different
chemical agents

6. What makes them different
0.2% solution of phenol is an antiseptic and
1.0% solution of phenol is a disinfectant.
A few agents are suitable as both
disinfectants and antiseptics
most disinfectants are too harsh
for use on delicate skin tissue

7. Factors influencing chemical agents
• Time: the length of time the organisms are
exposed to the antimicrobialagent
• Temperature: accelerated by increasing the
temperature
• pH: Incarease in pH
• Concentration: increasing concentration increase
the effects of most antimicrobial chemical agents

8. Soaps contain alkali and sodium and will
kill many species of Streptococcus,
Micrococcus, and Neisseria and will
destroy influenza viruses.
Soaps and Detergents

9. • Detergents are cationic and anionic
• Cationic detergents are used to sanitize food
utensils. Although not effective in killing
spores, they do inactivate some viruses.
• cationic detergents are quaternary
ammonium compounds of acetate and
chloride, that is they contain NH4+
• Cetyl tri methyl ammonium bromide
Soaps and Detergents

10. • Anionic detergents are used for laundering
clothes and as household cleaning agents.
They are less effective than cationic
detergents
• Sodium alkyl sulphates:- Sodium lauryl
sulphate
• Sodium alkylbenzene sulphonates:- Sodium
dodecyl benzene sulphonate
Soaps and Detergents

11. Acids and Alkalis
• Lactic and propionic acids retard mold growth in
breads and other products.
• Benzoic acid and several of its derivatives are
used to prevent fungal growth in soft drinks,
ketchup, and margarine.
• Sorbic acid and sorbates are used to prevent
fungal growth in cheeses
• Boric acid, formerly used as an eyewash, is no
longer recommended because of its toxicity
• Soap has mid alkalinity

12. Heavy Metals
• selenium, mercury, copper, and silver
• Even tiny quantities of heavy metals can be very
effective in inhibiting bacterial growth
• Silver nitrate
• Organic mercury compounds, such as
merthiolate and mercurochrome, are used to
disinfect surface skin wounds
• Selenium sulfide kills fungi, including spores.
Shampoos that contain selenium are effective in
controlling dandruff
• Copper sulfate is used to control algal growth

13. Heavy Metals

14. Halogens
• Hypochlorous acid, formed by the addition of
chlorine to water, effectively controls
microorganisms in drinkingwater and
swimming pools
• Iodine is an effective antimicrobial agent.
Betadine and Isodine are used for surgical
scrubs and on skin before surgery
• Chloramine, Bromine are other examples

15. Alcohols
• When mixed with water, alcohols denature
protein. They are also lipid solvents and
dissolve membranes
• Ethyl and isopropyl alcohols can be used as
skin antiseptics
• Alcohol disinfects but does not sterilize skin
because it evaporates quickly and stays in
contact with microbes for only a few seconds
• 70% ethyl alcohol is usually used to disinfect a
thermometer.

16. Phenols
• Phenol and phenol derivatives called
phenolics disrupt cell membranes, denature
proteins, and inactivate enzymes.
• Amphyl, which contains amylphenol, destroys
vegetative forms of bacteria and fungi and
inactivates viruses.

17. Phenols
• orthophenylphenol in Lysol
• Halogenated phenols, inhibit staphylococci
and fungi
• Trichlosan, made of two joined phenol rings

18. Oxidizing Agents
• disrupt disulfide bonds in proteins and thus
disrupt the structure of membranes and
proteins.
• Hydrogen peroxide (H2O2), which forms
highly reactive superoxide O2- is used to
clean puncture wounds
• very effective at disinfecting contact lenses
• Potassium permanganate, is used to disinfect
instruments and, in low concentrations, to
clean skin.

19. Alkylating Agents
• disrupt the structure of both proteins and
nucleic acids.
• Eg: Formaldehyde, glutaraldehyde, and b-
propiolactone are used in aqueous solutions.
Ethylene oxide is used in gaseous form.
It is exceedingly important that workers be
protected from ethylene oxide vapors, which are
toxic to skin, eyes, and mucous membranes and
may also cause cancer.

20. Dyes
• Acridine, can be used to clean wounds
• Methylene blue inhibits growth of some bacteria
• Crystal violet (gentian violet) blocks cell wall
synthesis. Used to treat yeast and protozoan
infections

21. Two different meaning..!
Bacteriostatic agent An agent that inhibits the
growth of bacteria.
Bactericide An agent that kills bacteria. Most
such agents do not kill spores

22. Mechanism of action
In denaturation, hydrogen and disulfide bonds
are disrupted, and the functional shape of the
protein molecule is destroyed.
There are two types of denaturation
Protein Denaturation

23. Mechanism of action
Protein Denaturation

24. Chemical agents Way of denaturation
Acids (boric acid, and
strong alkalis )
destroy protein by hydrolyzing
Oxidizing agents (H2O2) oxidize disulfide linkages
Halogens act as oxidizing agents
Heavy metals (Hg and Ag) attach to sulfhydryl groups.
Alkylating agents donate –CH3 groups to proteins
Halogens substituted for hydrogen in carboxyl
(-COOH), sulfhydryl, amino (—NH2),
and alcohol (—OH) groups
Mechanism of action
Protein Denaturation

25. Mechanism of action
Chemical agents can impart antimicrobial effect
by either destroying membrane proteins or
dissolving lipids
• Surfactants are soluble compounds that reduce surface
tension. They can dissolve lipids Eg: Quats, Soaps, Detergents
• Phenols and alcohols can denature protein and dissolve lipids
Reactions That Affect Membranes

26. Mechanism of action
Virus inactivation can be effected by destroying
either the viruses’ nucleic acid or their
proteins.
• Alkylating agents such as ethylene oxide, nitrous acid, and
hydroxylamine, act as chemical mutagens—they alter DNA or
RNA
• Detergents, alcohols, and other agents that denature
proteins
Reactions That Affect Viruses

27. ?
What are different
Physical agents
1. Dry heat, moist heat, and pasteurization
2. Refrigeration, freezing, drying, and freeze-drying
3. Radiation
4. Filtration
5. Sonic and ultrasonic waves
6. Osmotic pressure

28. • It is usually used to sterilize metal objects and
glassware and is the only suitable means of
sterilizing oils and powders
• Objects are sterilized by dry heat when
subjected to 171°C for 1 hour, 160°C for 2
hours or longer, or 121°C for 16 hours
Dry Heat

29. Dry Heat
Hot air oven is used for
dry heat sterilization

30. • because of its penetrating properties, is a
widely used physical agent
• At 15 lb/in the temperature reaches 121°C,
which kill spores, as well as living microbes,
and to disrupt the structure of nucleic acids in
viruses. This is achieved using autoclave
• heat-resistant endospores, such as those of
Bacillus stearothermophilus, to check
autoclave performance
Moist Heat

31. Moist Heat

32. Moist Heat

33. • a process invented by Pasteur to destroy
organisms that caused wine to sour
• Pasteurization does not sterilize a beverage, but it
does kill any pathogens present and drastically
slows spoilage by reducing the level of
microorganisms.
• Heated upto 60°C then cool down immediately
• Ultra high temperature (UHT) processing raises
the temperature from 74 to 140°C andthen drops
it back to 74°C in less than 5 sec.
Pasteurization

34. • Cold temperature retards the growth of
microorganisms by slowing the rate of enzyme-
controlled reactions but does not kill many
microbes
• Many fresh foods can be prevented from spoiling
by keeping them at 5°C
• storage should be limited to a few days because
some bacteria and molds continue to grow at this
temperature
Refrigeration

35. • Freezing at -20°C is used to preserve foods
• slow the rate of chemical reactions so that
microorganisms do not cause food to spoil
• Microorganisms are usually suspended in
glycerol or protein
• cooled with solid carbon dioxide (dry ice) -78°C
• they can be placed in liquid nitrogen and cooled
to -180°C.
F r e e z i n g

36. • the absence of water inhibits the action of
enzymes
• Yeast used in baking also can be preserved by
drying
• Treponema pallidum is sensitive to drying
• Drying of laundry in dryers or in the sunshine
also destroys pathogens
Drying

37. • is the drying of a material from the frozen state
• rapidly frozen in alcohol and dry ice or in liquid
nitrogen, are then subjected to a high vacuum
to remove all the water while in the frozen
state, and finally are sealed under a vacuum.
• Microbiologists use lyophilization for long-term
preservation of microbes
• Instant coffee, tea are made this way
lyophilization

38. • Four general types of radiation—ultraviolet light,
ionizing radiation, microwave radiation, and strong
visible light
• Ultraviolet (UV) light consists of light of
wavelengths between 40 and 390 nm but 200nm is
most lethal
• UV is absorbed by the purine and pyrimidine bases
of nucleic acids - permanently destroy these
molecules.
• Effective in inactivating viruses.
• Kills fewer bacteria because of DNA repair
mechanisms.
Radiation

39. • X rays (0.1 to 40 nm) and gamma rays
• Ionizing radiation damages DNA and produces
peroxides which act as powerful oxidizing
agents in cells
• It is used to sterilize plastic laboratory & medical
equipment and pharmaceutical products
Ionizing Radiation

40. • the passage of a material through a filter, or
straining device
• Membrane filters: used to sterilize materials
likely to be damaged by heat sterilization.
• Like media, special nutrients that might be
added to media, and pharmaceutical products
such as drugs, sera, and vitamins
• Cellulose acetate filters with extremely tiny
pores are capable of removing viruses from
liquids.
1Filtration

41. Some Defenitions
• Sterilization: The killing or removal of all microorganisms in a
material or on an object.
• Disinfection: The reduction of the number of pathogenic
microorganisms to the point where they pose no danger of disease.
• Antiseptic: A chemical agent that can safely be used externally on
living tissue to destroy microorganisms or to inhibit their growth.
• Disinfectant: A chemical agent used on inanimate objects to
destroy microorganisms. Most disinfectants do not kill spores.
• Sanitizer: A chemical agent typically used on food-handling
equipment and eating utensils to reduce bacterial numbers so as to
meet public health standards. Sanitization may simply refer to
thorough washing withonly soap or detergent.

42. Some Defenitions
• Bacteriostatic agent: An agent that inhibits the growth of bacteria.
• Germicide: An agent capable of killing microbes rapidly; some such
agents effectively kill certain microorganisms but only inhibit the
growth of others.
• Bactericide: An agent that kills bacteria. Most such agents do not
kill spores.
• Viricide: An agent that inactivates viruses.
• Fungicide: An agent that kills fungi.
• Sporocide: An agent that kills bacterial endospores or fungal
spores.