Sterilization and Disinfection Rashad Shawgi Babiker M.Sc. (Microbiology) (UMST) M.Sc. Stud. (Immunology ) Institute of Tropical Medicine.(SAS)

OUTLINES Bactericidal vs Bacteriostatic Sterilization vs Disinfection Sepsis, Aseptic and Antisepsis

Sterilization and disinfection

Sterilization 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

Disinfection removal or killing of disease-causing microorganisms Used to reduce number of viable microorganism .

Definitions Sepsis : infection Aseptic : without infection Antisepsis : any procedure that inhibits the growth and multiplication of microorganisms on body surface such as the skin

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 HEAT Incineration. 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}.??

Pasteurization < 100 °C Louis Pasture's discovery. Milk at 65 for 30 min

Boiling 100 °C 30 minutes of boiling kills microbial pathogens and vegetative forms of bacteria but may not kill bacterial endospores Tendelization !!

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)

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.

IRRADIATION Infrared radiation: temperature of objects rapidly Ultraviolet radiation 210–330 nm (blocks DNA replication-dimer formation-) Ionising radiation: X-ray and g-rays (high energy and penetration)

FILTRATION Temperature-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.

Chemicals Alcohols Phenols is used as a disinfectant standard. Chlorhexidine : useful topical disinfectant. Iodine : can cause hypersensitivity reactions. Chlorine : inactivates bacteria and most viruses Formaldehyde Ethylene oxide ((CH2)2O) : is an alkylating agent (heat-sensitive hospital instruments.)

Physical methods:- Method Temperature 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 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 Shadows and dust on the lamps can reduce effectiveness Has low penetrating power Limited usefulness Among least effective methods 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

Chemical 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