Department of Microbiology & Parasitology - Elrazi College

Definitions Sterilization: is complete killing, or removal, of all living organisms (including spores) from a particular location or material. Disinfection: 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. Asepsis: describes processes designed to prevent microorganisms from reaching a protected environment by application sterilization and disinfection procedures and protocols..

Sterilization by physical methods Heat: Dry Heat. Moist Heat. Radiation: Filtration: by chemical methods:

Sterilization by physical methods Dry heat: Red heat (flaming): Sterilize the metal objects like bacteriologic loops

Sterilization by physical methods Dry heat: 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 methods Dry heat: Incineration: Get rid of all disposal products in hospitals

Sterilization by physical methods Moist heat: 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. 74°C for 3 to 5 seconds (flash method). 62°C for 30 min (holder method). Organisms transmitted through consumption of milk: brucella sp. Listeria monocytogenes. coxiella burnetii mycobacterium bovis.

Sterilization by physical methods Moist heat: At 100ºC is called Boiling not efficient for eradication of endospores.

Sterilization by physical methods Moist heat: Autoclave: steam under pressure to raise the temperature to 121° C at 15-17 pounds psi for 10-15 minutes. suitable for eradication of endospores.

Sterilization by physical methods Autoclave: Tests for efficiency Chemical Chemical tapes Bowie Dick tapes Braun’s tubes

Sterilization by physical methods Autoclave: Tests for efficiency Principle: Prepare spore in tubes which contains (sugar & indicator). After autoclaving the tubes were incubated for 48 hrs. The change in colour of the indicator means that the spore had germinate and utilize the sugar so the process is failed Biological Spores of Bacillus stearothermophilus

Sterilization by physical methods Autoclave: Tests for efficiency Physical Graphs Digital

Sterilization by physical methods Tyndallization: Induction of the bacterial spore to develop into vegetative bacteria; that can be then killed by heating. Method: Repeated & alternating cooling & boiling of the medium will induce the spores to germinate into heat sensitive vegetative cells. Subsequent rounds of heating will sterilize the medium from the spores

Sterilization by physical methods Filtration: a pore size of 0.2 μm (retain all bacteria and spores). physically trapping particles larger than the pore size. retaining smaller particles via electrostatic attraction of the particles to the filters. Used for sterilization of solution like serum. Membrane filter. Syringe filter. Asbestos filter.

Sterilization by physical methods Filtration: HEPA filter High Efficient Particulate Air filter

Sterilization by physical methods Radiation: Ionizing Radiation. causes direct damage to DNA. produces toxic free radicals and hydrogen peroxide from water within the microbial cells. Used to sterilize plastic equipments like syringe , gloves and catheters

Sterilization by physical methods Radiation: Ultra-Violet radiation: Short wavelength 280 nm UV ray inhibit DNA replication (forming thymine dimers). For sterilization of operating theatre and theatre equipments.

Sterilization by Chemical methods Gaseous sterilization: Ethylene oxide: used in hospitals for sterilization of heat-sensitive materials like surgical instruments and plastics. It kills by alkylating both bacterial proteins and nucleic acids. Explosive and mutagen. Formaldehyde: available as a 37% solution in water (Formalin). denatures proteins and nucleic acids. Glutaraldehyde: more effective than formaldehyde and is less toxic. used to sterilize respiratory therapy equipment.

Chemical: Disinfectants Disinfectants: Chemicals used to decrease the chance of the micro-organisms to cause an infection. 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) acts by disrupting the lipid structure in membranes and denatures proteins. antiseptic to clean the skin prior to venipuncture.

Disinfectants Phenolics disinfectants; Phenol: Disinfectants, not used today. Hexachlorophene: Antispetic, effectiveness for skin flora and Gram positive cocci. Chlorhexidine: Antiseptic, broader activity and less toxic.

Disinfectants Glutaraldehyde decontaminate laboratory rooms

Chlorine is a powerful oxidizing agent. used as a disinfectant to purify the water supply and to treat swimming pools, home and in hospitals. hypochlorite (bleach, Clorox):

Disinfectants Iodine: the most effective skin antiseptic used in medical practice. Iodine forms: Tincture of iodine (2% solution of iodine and potassium iodide in ethanol) is used to prepare the skin prior to blood culture. Irritant. lodophors : complexes of iodine with detergents. frequently used to prepare the skin prior to surgery. less irritating than tincture of iodine.,

Groups of disinfectants: Parachlorometaxylenol (PCMX):  antibacterial action is due to disruption of cell membrane potentials

Hydrogen peroxide: