Importance of Microbial control!
- To prevent the spread of infectious diseases
- To prevent food spoilage
- To prevent disruptions or interference in an industrial process through contamination
- To prevent alteration of samples/results in laboratory settings
Sterilization
Killing all microbes present
Including spores
Disinfection
Removal of vegetative of pathogens from inanimate objects
Sanitization
reduction in number of microbes from inanimate objects present to safe (accepted) public health levels
By mechanical cleansing and physical methods
Ex: baby bottles
Sepsis
growth of microbes (presence of toxins) in tissue
Asepsis
techniques that prevent the entry of microorganisms into sterile tissue
Ex: washing, NO chemicals
Antisepsis
Application of chemicals to body surfaces to kill or inhibit microbes
Doesn’t cause damage to tissue
Ex: using chemical antiseptics
Aseptic Technique
Methods applied to an object or area to prevent microbial (pathogenic) contamination
Degerming
Cleansing techniques to remove transient microbes and debris from living tissue
Ex: showering
Bacteriocide
Chemicals that kill vegatative cells and may NOT kill the spores
“cide”: chemical that kills
Bacteriostat
Chemicals that stop or slow microbial growth
“stat”: prevents multiplication
Factors that Influence Microbial Control
- The number of microorganisms
- The type of microorganisms
- The nature of the suspending medium
- Determine the nature of the chemicals - Time
- Temperature
Types of Cellular Injury
- Alteration of membrane permeability
- Damage to cell wall
- Damage cell membrane
- Damage to proteins
- Damage to nucleic acids
Heat
- Most common method
- Most effective method
- Least expensive method
- Mode of action:
- Denaturing proteins (enzymes) of coagulation
ex: autoclave - Oxidizing of microorganisms
ex: burning
- Denaturing proteins (enzymes) of coagulation
Thermal Death Point (TDP)
*Lowest temperature at which all the microorganisms in a liquid suspension will be killed in 10 minutes
Thermal Death Time(TDT)
*Minimal length of time for all the microorganisms in a liquid suspension to be killed at a given temperature
Moist Heat–Autoclave
*Steam under pressure
*121 degrees C at 15 psi for 15-20 mins
*Destroys all forms-STERILIZATION
Test by: spore strips and heat sensitive paper
Moist Heat–Boiling
*98-100oC for 30 min
*Kills most vegetative cells not heat resistant forms
Ex: Sanitizing
Moist Heat–Tyndallization (Fractional Sterilization)
*Heating to 100oC for 30 min
*For 3 successive days
*Over night incubation periods in between
Ex: boil-sit and cool-boil-sit and cool etc
Moist Heat–Pasteurization
- Heating material at specific temp for a specific length of time and cool rapidly
- Temp. selection is based upon most resistant pathogen to be destroyed
- Coxiella Burnetti
- High Temp Short Term (HTST)
- 72oC for 15 sec
- Ultrahigh Temp (UHT)
- 140oC for 1-2 sec
Dry Heat–Hot Air Ovens
- 160-170oC for 2-3 hrs
- Oxidation of microbes
- Sterilizes
Dry Heat–Incineration’s (Direct Flame)
- Oxidation to ashes (burning) 1-60 minutes
* Temp may exceed 1000oC
Radiation
- Two types exist
* Rays less than 300 mm are effective for sterilization
Radiation–Ionizing rays (X-rays, gamma rays)
- Produces hyperactive ions and free radicals
* Destruction to DNA, denatures proteins
