This document discusses disinfection and the factors that influence it. Disinfection aims to inactivate or destroy microbes through physical, chemical, or biological processes. Early civilizations practiced various methods of preventing microbial growth like salting, smoking, and drying foods. Phenol was one of the earliest known disinfectants. The ideal disinfectant is broad-spectrum, fast-acting, effective in the presence of organic matter, and non-toxic. Concentration, time, pH, temperature, and the organism affect disinfection. Disinfection kinetics often follow Chick's law of first-order reactions. Common disinfectants discussed include UV light, gamma radiation, halogens like chlorine and iodine

2. INTRODUCTION
 Any process to destroy or prevent the growth
of microbes.
 Intended to inactivate the microbes by
physical, chemical or biological processes.
 Inactivation is achieved by altering or
destroying essential structures or functions
within the microbe.
 Proteins
 Nucleic acids
 Lipids

3. HISTORY
 Early civilization practiced salting, smoking,
pickling, drying, and exposure of food and
clothing to sunlight to control microbial growth.
 use of spices in cooking was to mask taste of
spoiled food.
 Phenol is probably the oldest known
disinfectant as it was first used by Lister.

4. DEFINITION
The selective elimination of certain undesirable
organisms in order to prevent their
transmission , achieved by action on their
structure or metabolism , irrespective of their
functional state.
- European committee
Disinfection dose not necessarily kill all
microorganisms but reduce them to a
acceptable level for a defined purpose.
- British standards

5. PROPERTIES OF IDEAL
DISINFECTANT
 Broad spectrum
 Fast action
 Effective in the presences of organic matter ,
suspended solids and other matrix or sample
constituents
 Nontoxic
 Soluble
 Non – flammable
 Non – explosive
 Compatible with various materials/surfaces

6.  Stable
 Easy to generate and apply
 Economical

7. FACTORS INFLUENCING
DISINFECTION
 Concentration of substance
 Time of action
 Ph of the medium
 Temperature
 Nature of the organism
 Disinfection kinetics

8. DISINFECTION KINETICS
Disinfection is a kinetic process where increased
inactivation with increased exposure or contact
accors.
which can be explained by chick’s law (First order
reaction)
disinfection kinetics are better in plug flow than in
batch
CT- concept :disinfection can be expressed at the
product of disinfectant concentration and contact
time (Applies when disinfection kinetics is of first
ordre)

9. Batch mixed reactor
and plug flow or pipe
reactor
Disinfection kinetics

10. CHICK’S LAW
Assumptions of law
 All organisms identical
 Death or inactivation results from a first order or single
hit
chick’s law
dN/dT =N
Where ,N =number of organisms
T = time
In Nt /No = -Kt
Where ,No =initial number of organism
Nt = number of remaining at time t

11. UV LIGHT
 UV light is a electromagnetic radiation with a
wave length of approximately 200 -400 nm.
 It has been used since the early 1900s in
Europe for the disinfection of municipal water
supplies.
 UV light disinfects by altering the DNA of the
bacterial cells that are exposed.
 In waste water treatment plants, UV light is
produced by low pressure mercury lamps .

12. UV DISINFECTION
LOW PRESSER
- -Wavelength at 254nm
- -Low intensity
- MEDIUM PRESSURE
- -Wavelength between 100 to 1000nm
- -High intensity
- PULSED UV
- -intermittent emission
- -High intensity

13. EFFECT OF UV RADIATION

15. GAMMA RADIATION
Gamma irradiation is an electromagnetic
radiation of short wave length emitted by
radioactive isotopes. It is widely used for the
sterilization of medical devices , food
preservation etc , Gamma radiation may be in
the form of Cobalt-60 or Caesim-137.

16. MECHANISM
The microorganisms are killed by direct or
indirect damage to its DNA. The propagation
of of life is arrested due to DNA impairment by
the ionizing radiation. The direct effect are due
to damage to DNA may be as single break ,
double break , base damage , intra or inter
molecular crosslink formation. And indirect
effect are due to free radicals formed due to
radiolysis of water.

17. PHOTODYNAMIC INACTIVATION
Photodynamic inactivation is a phenomenon that
has the potential to cause microbial
inactivation using visible light.
PRINCIPLE
PDI occurs when light of specific wavelength
triggers a series of oxidative reactions inside a
microbial cell. Light sensitive compounds
known as photosensitizers (PSs) help trigger
these reactions. These PSs may be present
naturally in side the cell (endogenous) or may
be externally supplied (exogenous).

18. Photodynamic inactivation of cell

19. DISADVANTAGES
 High cost of operation.
 Anything that can prevent the UV from
reaching the bacteria will prevent an effective
kill.
 UV light tends to ionize compounds and break
them.

20. HALOGENS
Halogens are Fluorine ,Chlorine , Bromine and
Iodine
Occurrence -sea water and salts
State - Ionic and non ionic state
They are highly effective components of
disinfectants and antiseptics because they are
microbicidal not microbistatic.
Chlorine and iodine are the two routinely used
halogens because Bromine and Fluorine are
difficult to handel.

21. CHLORINE AND ITS COMPOUNDS
 Chlorine has been used for disinfection for 200
years.
 Major forms used are Hypochlorite and
chloramines
 It not only kills endospores but also fungi and
viruses .
 Chlorine compounds are used for large scale
disinfection of drinking water , sewage , etc .
 Hypochlorite are most extensively used of all
chlorine compounds.

22. IODINE AND ITS COMPOUNDS
 Iodine is pungent black chemical that form
brown colored solution when dissolved in
water or alcohol.
 2% free iodine and 2.4% sodium iodide are
used as antiseptic before surgery.
 It kill all microorganisms if optimum
concentration is used.
 Iodine tincture is 2% solution of iodine.
 Sodium iodine in 70% alcohol can be used as
disinfectant.

23. CHLORINE
 Chlorine kills pathogens such as bacteria and
viruses by breaking the chemical bonds in their
molecules.
 The recommended concentration for disinfection
is 600-800ppm of chlorine bleach and 50 to
200ppm for sanitizing
 Disinfection of water with chlorine is generally
reffered as chlorination.
 Chlorine was first used as a disinfectant around
1800A.D
 The primary use of chlorine in sewage disposal
system was for odor control.

24.  Although chlorine is a strong oxidizing agent its
toxicity against microorganisms is not due to its
oxidation effect. It interferes with vital enzymes of
microorganisms and brings out their death.
 Chlorine when added to water undergoes various
reactions with water and other constituents of
water
 The first important reaction is the formation of
hypochlorous acid (HOCL)
 HOCL is a week acid and often dissociates into
H+ and OCL ions
 The extent of dissociation depends on the ph (6.7)
 In the presence of ammonia in water
hypochlorous acid reacts with ammonium ion and
successively gives monochloramine ,
dichloramine and trichloramine.

25. CHLORINE DIOXED
 Chlorine dioxide is treated as a separate
disinfectant since it is not formed by direct
addition of chlorine to water.
 Chlorine dioxide can be generated by adding
either chlorine or hydrochloric acid in sodium
chlorite.
 Chlorine dioxide is a more powerful
disinfectant than chlorine in alkaline
conditions.
 The disadvantage id it is more expensive.

26. ADVANTAGES
 It is readily available as gas, liquid, and power
 Cheap
 Solubility (700mg/ltr)
 Not harm human.
 Toxic to most microorganisms, interfering with
their metabolic activity
 Plays important role in treatment of cyanide
waste which are highly toxic

27. DISADVANTAGES
 It is a toxic gas and need careful handling
 It can cause taste and odor problems

28. OZONE
Ozone is a blue gas, with a density greater than air ,
making it ideal disinfectant for both air and water.
It kills single and multicellular organisms with low
cell specialization.
Eg – bacteria, viruses(including COVID-19) and
fungi
Ozone is a powerful oxidizing agent, which naturally
destroys harmful microorganism through
oxidation.
Formed by passing dry air through high voltage
electrodes which is bobbled into water need to be
treated.

29. PROPERTIES
 Colorless gas
 Relatively unstable
 Reacts with itself and OH ions in water
 Less stable at high ph

30. DOMESTIC AND INDOOR
MICROBIOLOGY

31. INTRODUCTION
80% or more of all common infections including
colds, flu, skin infections, and diarrhea
acquried by exposure to our environment.
Since humans in developed countries spend
from 35% to 90% of their times indoor, sources
of infection can be air, water, food etc which
enters the home.
Once inside the home infection can transfer from
person to person via contact or via person –
fomite – person .

32. HOUSEHOLD SOURSE OF
PATHOGENS
1. AIR
Microbial airborne pathogens occur as bioaerosols and
include bacteria, viruses, molds and spores . Molds
are fungi that include species of penicillium ,
aspergillus ,and alternaria etc . Molds are highly
prevalent in damp areas of home . Since moulds
reproduce via spores that are easily wind born, they
can easily enter home.
Molds cause variety of health concerns including nasal
stuffiness, eye irritation, skin irritation etc
Pathogens, including virus and bacteria, can also be found
in household air ,for example influenza , colds ,
chicken pox and tuberculosis are transmitted within
household .

33. 2. FOOD
Over 47 million cases of food illness will accur
every year in United States (2013). All types of
food can be associated with food born illness .
Common pathogenic microbes in food include
salmonella , campylobabter Listeria ,
staphylococcous and E .coli . salmonella is
found in poultry and seafood. Listeria is found in
raw milk, cheeses, ice cream, poultry and
smoked fish which causes meningitis and
encephalitis .This organism can grow at
3degerees. However, the major cause of
outbreak is because of food handling from
infected person, from water or from other

34. 3. WATER
Water distribution system are clearly a source of
microorganisms, but they appear to be no threat to
normal healthy human. General groups of bacteria
capable od specific biochemical transformation such
as sulfate reduction and nitrification have been
identified in tap water. Legionella pneumophila and
acanthamoeba spp. Are the only commonly associated
with illness. Legionella is associated with respiratory
illness from exposure to warm water. Acanthamoeba
Infection is associated with person who use tap water
to wet their contact lenses.

35. FOMITES : ROLE IN
DESEASE SPREAD
Fomites are believed to play an important role in
transmission of some pathogens, which may
include doorknobs, sink taps, cutting boards,
computer key boards and toilet seats etc .
Fomites can also result in cross contamination
from food.

37. OCCURRENCE OF
PATHOGENS ON FOMITES
Fomites may became contaminated with pathogens by
direct contact with body secretions or airborne
organisms may settle on surface. Fomites may also
serve as a site for the replication of pathogens. Until
the development of molecular methods, such as PCR,
data on the occurrence of pathogen on fomites were
very limited because of difficulty and cost associated
with the isolation of pathogens. Coliform bactria in
households are found in high concentration on kitchen
sponges, sink , bathroom area etc.Enteric bacteria are
bought in home by raw meat and vegetables and
spread around home during normal cleaning of
surface, public toilet are responsible for
epidemiological out break of shigella.

38. PERSISTENCE OF
PATHOGENS ON FOMITES
The persistence of pathogen on a fomite is
dependent on several factors
- The rate of drying.
- Temperature
- Humidity

39. TRANSFER OF PATHOGENS
Studies have shown that the degree of virus transfer
is related to
 AGE - an increase in age of an individual
reduces the relative amounts transferred probably
because of less moisture in the skin.
 The amount of pressure applied.
 The application of friction which substantially
increases the amount of transfer.
 The degree of transfer of any organism will
depend on the nature and type of organism.

40. Higher bacterial transfer rates from fomite to hand
have been observed with hard nonporous surface
( phone receiver, laptop etc ) than with the porous
surfaces ( clothing, sponges)

42. Children younger than 6 years old were randomised
by alternate house hold to drink water either left in
plastic bottles exposed to sunlight or kept indoore
(control).
The children drinking solar disinfected water had a
significantly lower risk of severe diarrhoeal
disease.
It confirms solar disinfection as effective in vivo as a
free, low technology, point of consumption method
of improving water quality. The continuing use of
solar disinfection by the community underlines the
value of community participation in research.

43. Children younger than 6 years old were randomised
by alternate house hold to drink water either left in
plastic bottles exposed to sunlight or kept indoore
(control) .
The children drinking solar disinfected water had a
significantly lower risk of severe diarrhoeal
disease.
It confirms solar disinfection as effective in vivo as a
free, low technology, point of consumption method
of improving water quality. The continuing use of
solar disinfection by the community underlines the
value of community participation in research.

44. RESULT
Out of 349 children in 140(40.11%) households
170 were girls with mean age 2.4 and
179(51.28%) were boys with mean age 2.6.
Half of 349 were given solar disinfected water
and half were given indoor( control) water and
found that 42% of children who were given
solar disinfected water was not infected and
73% of children who drank indoor water were
infected.

45. CONCLUSION
Laboratory studies of solar disinfection using
plastic bottles have demonstrated significant
reductions in bacterial contamination even in
high turbid water. The result presented here
confirm the utility of solar disinfection reduced
the risk of diarrhoea in children.