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Rashad Shawgi BabikerM.Sc. (Microbiology)

(UMST)M.Sc. Stud. (Immunology )Institute of Tropical Medicine.

(SAS)

OUTLINES

Bactericidal vs Bacteriostatic

Sterilization vs Disinfection

Sepsis, Aseptic and Antisepsis

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Sterilization

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a process whereby an item is

freed of any living micro-

organism or their dormant stage.

Sterility

total absence of viable

microorganisms as assessed by no

growth on any medium

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Disinfectionremoval or killing of disease-causing

microorganisms

Used to reduce number of viable

microorganism .

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Definitions Sepsis : infection

Aseptic : without infection

Antisepsis : any procedure that

inhibits the growth and multiplication

of microorganisms on body surface

such as the skin7

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Physical Sterilization sterilization by heat

Thermal death point :- This the lowest temperature above the

optimum temperature , at which the growth of microorganism stops, and death occurs in a given time.

Thermal death time:-This the shortest time at which growth of

microorganism stops & death occurs at a certain temperature .

DRY HEATIncineration.

Red heat (Bunsen flame) includes

sterilization of wires ,forceps ,

needles etc

hot-air ovens are usually held at

160–180°C for 2 hours. {plastics}.??10

Pasteurization < 100 °C Louis Pasture's discovery.

Milk at 65 for 30 min

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Boiling 100 °C 30 minutes of boiling kills microbial

pathogens and vegetative forms of bacteria but may not kill bacterial endospores

Tendelization !!

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Autoclaving > 100 °C

Moist heat (autoclaving at 121°C for 15 minutes at a steam pressure of 15 pounds per square inch kills microorganisms, including endospores)

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Control Although measurements of the

temperature are important, biological controls offer a direct measure of the sterilising power of the system.

For this purpose suspensions of bacterial spores (commonly Bacillus stereothermophilus spores) as well as control strips.

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IRRADIATIONInfrared radiation: temperature of

objects rapidlyUltraviolet radiation 210–330 nm

(blocks DNA replication-dimer formation-)

Ionising radiation: X-ray and g-rays (high energy and penetration)

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FILTRATIONTemperature-sensitive substances

such as carbohydrates and amino acids

that will be destroyed by heat

sterilisation need to be sterilised by

filtration.

The pore size (0.2 μm) will prevent

bacteria passing through the filter.16

ChemicalsAlcoholsPhenols is used as a disinfectant standard.Chlorhexidine : useful topical disinfectant.

Iodine : can cause hypersensitivity reactions.

Chlorine : inactivates bacteria and most viruses

FormaldehydeEthylene oxide ((CH2)2O) : is an alkylating

agent (heat-sensitive hospital instruments.)17

MethodTemperature

Effectiveness Use

Boiling 100o

30 minutes of boiling kills microbial pathogens and vegetative forms of bacteria but may not kill bacterial endospores

Syringes

Intermittent boiling

100o

Three 30-minute intervals of boiling, followed by periods of cooling kills bacterial endospores

To kills bacterial endospores

Autoclave and pressure cooker (steam under pressure)

121o/15 minutes at 15# pressure

kills all forms of life including bacterial endospores. The substance being sterilized must be maintained at the effective T for the full time

Cultures, lab glassware, pipettes, syringes, or other small items

Physical methods:-

Method Acceptable for... How? Special Precautions Comments

Ionizing Radiation

Prepackaged medical devices, including operating room supplies such as syringes and catheters

  None Not a practical tool for the laboratory

Ultraviolet Radiation

Within BSCs to maintain low levels of contamination

Installation of a lamp in BSC 1.Shadows and dust on the

lamps can reduce effectiveness 2.Has low penetrating power

1.Limited usefulness 2.Among least effective methods 3.Not practical for liquids

Filtration Removal of bacteria, yeast, and molds from biological and pharmaceutical solutions

Common pore sizes are 0.22 µm, 0.45 µm, and 0.8 µm

   

Physical methods:-

Method Acceptable for... How?Special Precautions

Comments

Glutaraldhyde Glassware and instruments; items that can be submerged and soaked in a covered container; considered a sporacidal

2% concentration for 10-600 minutes; rinse with sterile water to remove residuals

Sensitivity problems have developed in workers using it at high levels

 

Phenolic Compounds

General use on walls, floors, bench tops; bacteria; fungi; and lipid-containing viruses

0.2-3% concentration for 10-30 minutes

Can cause depigmentation, occupational leukoderma, idiopathic neonatal hyperbilirubinema

Not active against spores or non-lipid viruses

Chemical methods:-