Department of Microbiology & Parasitology - Elrazi College

Definitions o Sterilization:

o is complete killing, or removal, of all living organisms (including spores) from a particular location or material.

o Disinfection:o is the killing of many, but not all microorganisms , or

it is the destruction of pathogenic microorganisms by processes that fail to meet the criteria for sterilization.

o Asepsis:o describes processes designed to prevent

microorganisms from reaching a protected environment by application sterilization and disinfection procedures and protocols..

Sterilization

o by physical methodso Heat:

oDry Heat.oMoist Heat.

o Radiation:o Filtration:

o by chemical methods:

Sterilization by physical methods

o Dry heat:o Red heat (flaming):

Sterilize the metal objects like bacteriologic loops

Sterilization by physical methodso Dry heat:

o Hot air oven:

Temperature used 170º C for 1 hour or 160°C for 2 hours.

applicable to metals and laboratory glassware

Sterilization by physical methodso Dry heat:

o Incineration:

Get rid of all disposal products in hospitals

Sterilization by physical methodso Moist heat:

o Pasteurization is the use of heat at a temperature sufficient to inactivate important pathogenic organisms in liquids (milk) but at a temperature below that needed to ensure sterilization.

o 74°C for 3 to 5 seconds (flash method).o 62°C for 30 min (holder method).

o Organisms transmitted through consumption of milk:obrucella sp.o Listeria monocytogenes.o coxiella burnetiiomycobacterium bovis.

Sterilization by physical methods

o Moist heat:

o At 100ºC is called Boiling not

efficient for eradication of

endospores.

Sterilization by physical methods

o Moist heat:o Autoclave:

o steam under pressure to raise the temperature to 121° C at 15-17 pounds psi for 10-15 minutes.

o suitable for eradication of endospores.

Sterilization by physical methodso Autoclave: Tests for efficiency

Chemical

Chemical tapesBowie Dick tapes

Braun’s tubes

Sterilization by physical methodso Autoclave: Tests for efficiency

Biological

Spores of Bacillus stearothermophilus

oPrinciple:oPrepare spore in tubes

which contains (sugar & indicator).

oAfter autoclaving the tubes were incubated for 48 hrs.

oThe change in colour of the indicator means that the spore had germinate and utilize the sugar so the process is failed

Sterilization by physical methodso Autoclave: Tests for efficiency

Physical

Digital Graphs

o Tyndallization:o Induction of the bacterial spore to develop into

vegetative bacteria; that can be then killed by heating.

o Method:

oRepeated & alternating cooling & boiling of the medium will induce the spores to germinate into heat sensitive vegetative cells.

oSubsequent rounds of heating will sterilize the medium from the spores

Sterilization by physical methods

Sterilization by physical methodso Filtration: o a pore size of 0.2 μm (retain

all bacteria and spores).o physically trapping particles

larger than the pore size.

o retaining smaller particles via electrostatic attraction of the particles to the filters.

o Used for sterilization of solution like serum.

o Membrane filter.o Syringe filter.o Asbestos filter.

Sterilization by physical methodso Filtration:

HEPA filter

High Efficient Particulate Air filter

Sterilization by physical methodso Radiation:

o Ionizing Radiation.o causes direct damage to DNA.oproduces toxic free radicals

and hydrogen peroxide from water within the microbial cells.

o Used to sterilize plastic equipments like syringe , gloves and catheters

Sterilization by physical methods

o Radiation:o Ultra-Violet radiation:

o Short wavelength 280 nm UV ray inhibit DNA replication (forming thymine dimers).

o For sterilization of operating theatre and theatre equipments.

Sterilization by Chemical methods

o Gaseous sterilization:o Ethylene oxide:

o used in hospitals for sterilization of heat-sensitive materials like surgical instruments and plastics.

o It kills by alkylating both bacterial proteins and nucleic acids.

o Explosive and mutagen.

o Formaldehyde:o available as a 37% solution

in o water (Formalin).o denatures proteins and

nucleic acids.

o Glutaraldehyde:o more effective than

formaldehyde and is less toxic.

o used to sterilize respiratory therapy equipment.

Chemical: Disinfectants

o Disinfectants: Chemicals used to decrease the chance of the micro-organisms to cause an infection.

o Antiseptics: disinfectant agents that can be used on body surfaces such as the skin or mucous membrane to reduce the numbers of normal flora and pathogenic contaminants

Disinfectants Ethyl alcohol 70%(isopropyl alcohol)

o acts by disrupting the lipid structure in membranes and denatures proteins.

o antiseptic to clean the skin prior to venipuncture.

Disinfectants o Phenolics disinfectants;o Phenol:

o Disinfectants, not used today.

o Hexachlorophene:o Antispetic, effectiveness for

skin flora and Gram positive cocci.

o Chlorhexidine:o Antiseptic, broader activity

and less toxic.

Disinfectants o Glutaraldehyde

o decontaminate laboratory rooms

o Chlorine o is a powerful oxidizing agent.o used as a disinfectant to purify

the water supply and to treat swimming pools, home and in hospitals.

o hypochlorite (bleach, Clorox):

Disinfectants o Iodine:o the most effective skin antiseptic used in

medical practice.o Iodine forms:

1. Tincture of iodine (2% solution of iodine and potassium iodide in ethanol) is used to prepare the skin prior to blood culture. Irritant.

2. lodophors :o complexes of iodine with detergents.o frequently used to prepare the skin prior

to surgery.o less irritating than tincture of iodine.,

o Groups of disinfectants:o Parachlorometaxylenol (PCMX):o antibacterial action is due to

disruption of cell membrane potentials

o Hydrogen peroxide: