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1
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.
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
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
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:-