Chapter 8 – control of micro-organisms in the environment
, Mechanical removal methods Physical control methods
• Filtration • Heat and radiation
- Heat-sensitive liquids and air - Moist heat
- Porous membrane filters with defined pore sizes (0.2- o Destroys viruses, fungi, and bacteria
0.5 µm) that remove micro-organisms primarily by o Boiling will not destroy spores and does not
physical screening sterilize (just disinfection)
- 0.2 µm in diameter is used to remove most vegetative o Degrades nucleic acids, coagulates and
cells, but not viruses denatures proteins, and disrupts membranes
- Dry heat sterilization
o Less eFective than moist heat, requiring higher
temperatures and longer exposure times
o Items subjected to 160-170°C for 2 to 3 hours
o Dehydrates the cell, oxidizes cell constituents
and denatures proteins
• Surgical masks
• Cotton plugs on culture vessels
• Pasteurization
• High-eFiciency particulate air
- Controlled heating at temperatures well below boiling –
(HEPA) filters
- Used in laminar flow brief heating at 55-60°C for 30 minutes
biological safety cabinets - Used for milk, beer, and other beverages
- Does not sterilize but kill most pathogens – slows down
spoilage by non-spore forming pathogens by reducing
the total load of organisms present
, Mechanical removal methods Physical control methods
• Filtration • Heat and radiation
- Heat-sensitive liquids and air - Moist heat
- Porous membrane filters with defined pore sizes (0.2- o Destroys viruses, fungi, and bacteria
0.5 µm) that remove micro-organisms primarily by o Boiling will not destroy spores and does not
physical screening sterilize (just disinfection)
- 0.2 µm in diameter is used to remove most vegetative o Degrades nucleic acids, coagulates and
cells, but not viruses denatures proteins, and disrupts membranes
- Dry heat sterilization
o Less eFective than moist heat, requiring higher
temperatures and longer exposure times
o Items subjected to 160-170°C for 2 to 3 hours
o Dehydrates the cell, oxidizes cell constituents
and denatures proteins
• Surgical masks
• Cotton plugs on culture vessels
• Pasteurization
• High-eFiciency particulate air
- Controlled heating at temperatures well below boiling –
(HEPA) filters
- Used in laminar flow brief heating at 55-60°C for 30 minutes
biological safety cabinets - Used for milk, beer, and other beverages
- Does not sterilize but kill most pathogens – slows down
spoilage by non-spore forming pathogens by reducing
the total load of organisms present
