Physical and biological methods of sterilization and disinfection

Question 1

Physical methods

Answer 1

• tools (metal), fixtures, waste materials, clothing
• heat
• irridation
• ultraviolet light
• other methods: ultrasonography (gr - more susceptible), high pressure, microwaves (only vegetative form)

Question 2

Heat

Answer 2

◦ Destruction of proteins and enzymes
◦ Wet heat treatment is more effective than dry
◦ Vegetative forms - low resistance
◦ ad mixture of chemicals: increase effectiveness
–> 2% Sodium bicarbonate, 0,2% formalin (require proper ventilation), 0,5% sterogenol
◦ Bacteria:
‣ 58-60°C=30-60mins
‣ 70°C=5-10mins
‣ 100°C=onseconds
‣ Staph, Pseudomonas, Mycobacteria are more resistant
‣ Spores are more resistant: 100°C 20mins, Clostridia more than 3h
◦ Viruses: 50-60°C, some even 80°C
◦ Fungi: 50-60°C, moulds 100°C 90mins
◦ In practice, Commonly used methods:
->autoclave ,ironing, high pressure steam cleaner, burning

Question 3

Irridation

Answer 3

◦ Electromagnetic radiation
◦ Rontgen and gamma- rays 
◦ Irreversible changes in the structure of the proteins and DNA 
◦ + free radical
◦ Food – 10 kGy (kilo-Gray)
◦ Feedstuff, SPF – 25kGy
◦ medicaments, vaccines, diagnostic tools - 25kGy
◦ Slurry – 3-6kGy – dairyfarms
◦ >45 kGy wish of radiation

Question 4

Ultraviolet light

Answer 4

◦ Sunshine
◦ Germicidal lamp
◦ 250–260nm wave length is the most effective
◦ Inactivation of DNA
◦ Surface
◦ Only in clean environment (operating room, milking parlour)!!
◦ Dangerous – eyeproblems – careful use!

Question 5

Biological methods

Answer 5

• Feedstuff/ Manure fermentation 
◦ Competition
◦ Heat production
◦ Antimicrobial metabolites  
◦ pH
◦ Changing environment--> Corn silage