Physical methods of Disinfection

Dr Kiran KS

Department of Oral & Maxillofacial Surgery

Definition

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

Classification

• Cleaning

• Sunlight

• Desiccation

• Heat

• Filtration

• Radiation

CLEANING

Cleaning

• Widely used.

• Cheapest

• Detergents & their disinfectant property.

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.

Classification of detergents

• Those which ionize with the detergent property resident in the anions – anionic detergents.

• Eg: soap, sodium lauryl sulfate.

Classification…con

• Those which ionize with the detergent property resident in cation- cationic detergents

• Eg: Cetyl pyridinium chloride (Ceepryn)

Classification con…

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

Cleaning cont.

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

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.

Surface tension

• Decrease in ST Alter permeability characteristics of cytoplasmic membrane

Leakage of cellular substance damage to cell

Ultrasonic cleaners

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

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.

HAND RUB

HAND WASHING

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.

• 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 beginingwith hands & working towards the elbow.

• Apply gloves in an aseptic manner.

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

SUNLIGHT

Sunlight

• Active germicidal action , due to content of UV rays.

• Natural method of sterilization in case of water in tanks, river & lakes.

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.

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.

Radiation

• Mode of transmission of energy through space.

• Less energetic, nonionizing- UV radiation

• UV radiation is absorbed specifically by different compounds.

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.

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.

Application

Heat

• Microbes can grow over a range of temperatures.

• Psychrophiles- very low temperature.

• Mesophiles- moderate temperature (body temperature)

• Thermophiles- very high temperature.

BOILINING

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.

Pasteurization

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

Vaccine bath

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

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.

BACTERIOLOGICAL FILTERS

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.

HEPA filters

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

Bibliography

• Ananthanarayan & Paniker’s Text Book of Microbiology.

• Microbiology – Michael J. Pelczar, JR. , E.C.S. Chan, Noel R. Krieg.