This document discusses various physical methods of disinfection, including cleaning, sunlight, desiccation, heat, filtration, and radiation. Cleaning is the most widely used and inexpensive method, using detergents to remove microbes from surfaces through emulsification. Heat can also be used for disinfection through boiling, pasteurization, or vaccine/serum baths. Other methods like sunlight, desiccation, and radiation work by damaging microbial cells and inhibiting replication through UV absorption or drying. Filtration methods like HEPA filters provide sterile air through particulate removal.

1. Physical methods of Disinfection
Dr Kiran KS
Department of Oral & Maxillofacial
Surgery

2. Definition
• Disinfection is the destruction or removal of
all pathogenic organisms or organism capable
of giving rise to infection, but not necessarily
spores.

3. Classification
• Cleaning
• Sunlight
• Desiccation
• Heat
• Filtration
• Radiation

4. CLEANING

5. Cleaning
• Widely used.
• Cheapest
• Detergents & their disinfectant property.

6. Cleaning cont.
• Surface tension depressants, or wetting
agents –cleaning – ‘surfactants’ or ‘synthetic
detergents’.
• Extensively used in laundry and dishwashing
powders, shampoos and other washing
preparations.

7. Classification of detergents
• Those which ionize with the detergent
property resident in the anions – anionic
detergents.
• Eg: soap, sodium lauryl sulfate.

8. Classification…con
• Those which ionize with the detergent
property resident in cation- cationic
detergents
• Eg: Cetyl pyridinium chloride (Ceepryn)

9. Classification con…
• Non-ionic detergents, they do not ionize and
do not possess significant antimicrobial
property.

10. Cleaning cont.
• Removal of microbial flora from surfaces such
as skin and clothing- soaps- mechanical
removal.

11. Cleaning cont.
• Soaps reduce surface tension- increase
wetting power of water in which they are
dissolved – soapy water, emulsify and disperse
oil and dirt – microorganisms get enmeshed in
the soap lather and are removed by rinsing
water.

13. Surface tension
• Decrease in ST Alter permeability
characteristics of cytoplasmic membrane
Leakage of cellular substance damage to cell

14. Ultrasonic cleaners
• Ultrasonic cleaning recommended- in initial
removal of bio- burden ,while reducing hand
contact with potential injury causing reusable
sharps.

15. Hand washing
• “hand washing is considered to be one of the
most important procedures in prevention of
infections”.
• Mere mechanical action of rubbing the hands
together and rinsing them under running
water is an important aspect in removal of
transient organisms.

16. HAND RUB

18. HAND
WASHING

19. Technique
• Remove jewellery & check hands for cuts &
abrasions.
• Trim & clean finger nails, false fingernails or
nail polish should not be used.
• Scrub hands & forearm with approved liquid
soap & iodophores alternatively & repeatedly
for 7 minutes, washing away the lather each
time.

20. • Always rinse from fingertip proceeding to
elbow ,keeping the elbow raised.
• Allow water to drip from elbow & not from
hand.
• Dry hands first , with sterile towel begining
with hands & working towards the elbow.
• Apply gloves in an aseptic manner.

21. • Repeat hand washing between patient
appointments, before handling records,
before lunch, after a break in routine, &
before leaving the clinic.

23. SUNLIGHT

24. Sunlight
• Active germicidal action , due to content of UV
rays.
• Natural method of sterilization in case of
water in tanks, river & lakes.

25. Desiccation
• Cessation of metabolic activity- decline in total
viable population.
• Time of survival of microorganism after
desiccation depends on;
1. Kind of organism.
2. Material in or on which the organisms are dried.
3. Completeness of drying process.
4. Physical conditions to which dried organisms are
exposed eg., light, temperature , humidity.

26. Desiccation cont.
• Species of Gram negative cocci such as
gonococci and meningiococci are very
sensitive to dessication.
• Streptococci are more resistant.
• Dried spores remain viable, indefinitely.

27. Radiation
• Mode of transmission of energy through
space.
• Less energetic, nonionizing- UV radiation
• UV radiation is absorbed specifically by
different compounds.

28. UV light
• 150- 3900 A- UV spectrum
• 2650 A , highest bactericidal action.
• UV light has limited penetration, even a thin
layer of glass, filters off large percentage of
light.
• Microorganisms on the surface are
susceptible.

29. Mode of action
• Absorbed by cellular materials , specially
nucleus- damages the cell.
• Pyrimidine of nucleic acid absorbs UV
radiation – forms ‘pyrimidine dimer’(adjacent
2 pyrimidine's become bonded) unless dimers
are removed by specific intercellular enzyme;
DNA replication is inhibited and mutation
results.

30. Application

33. Heat
• Microbes can grow over a range of
temperatures.
• Psychrophiles- very low temperature.
• Mesophiles- moderate temperature (body
temperature)
• Thermophiles- very high temperature.

34. BOILINING

35. Boiling water
• Uncertainty in sterilization exist.
• 90-100 degree, 10- 30 min
• All vegetative spores gets destroyed when
exposed to boiling water ,but some bacterial
spores can withstand this condition for hours.
• Dis adv: makes surgical instruments blunt.

37. Pasteurization

38. pasteurization
 Milk, cream and certain alcoholic beverages (beer
and wine) are subjected to controlled heat
treatment called pasteurization.
 Milk heated at 63 degree for 30 mts.(holder
method)
 72 degree for 15- 20 sec (flash process)
 Followed by cooling to less than 13 degree , all the
nonsporing pathogens – Mycobacterium,
Brucellae, Salmonella are destroyed

42. Vaccine bath
• Vaccines of nonsporing bacteria are
inactivated in special vaccine bath at 60
degree for 1 hour.

43. Serum bath
• Serum or body fluids contain coagulable
proteins can be sterilized by heating for 1 hour
at 56 degree in water bath on several
successive days.

44. BACTERIOLOGICAL FILTERS

45. Bacteriological filters
• HEPA filters.
• High Efficiency Particulate Air Filter has made
it possible to deliver clean air to an enclosure
such as cubicle or a room.

48. HEPA filters
• HEPA filtration + system of laminar airflow is
used now, extensively to produce dust and
bacteria free air.

51. Bibliography
• Ananthanarayan & Paniker’s Text Book of
Microbiology.
• Microbiology – Michael J. Pelczar, JR. , E.C.S.
Chan, Noel R. Krieg.