Continuing Chapter 6
Estimating Bacterial Numbers by Indirect Methods
Turbidity - measurement of cloudiness with a spectrophotometer
Metabolic activity - mount of metabolic product is proportional to the number of bacteria
Dry weight - bacteria are filtered, dried, and weighed; used for filamentous organisms
Chapter 7 The Control of Microbial Growth
Tables 7.5 or 7.8, and study questions at the end of the chapter
The terminology of Microbial Growth
Sepsis refers to bacterial contamination
Asepsis is the absence of significant contamination
o Aseptic surgery techniques prevent the microbial contamination of wounds
o Not sterilization, but controlling it
Sterilization : removing and destroying all microbial life
o All vegetative and non vegetative forms
o Uses sterilant
Commercial sterilization: killing Clostridium botulinum endospores from canned goods
o Getting rid of endospores that cause spoilage in food
Disinfection: destroying harmful microorganisms
o Removing from surfaces, non living tissues
Antisepsis: destroying harmful microorganisms from living tissue
Disinfectant (non living tissue) can be the same as antiseptic (on living tissue) but a
disinfectant can be harsher on living tissue
Degerming: the mechanical removal of microbes from a limited area
o Wiping off from a small area (ie swabbing alcohol when giving an injection)
Sanitization: lowering microbial counts on eating utensils to safe levels
o Ex: washing dishes, use of disinfectants
, o Not sterilizing, but decreasing microbial counts to prevent the transmission of
disease
Biocide (germicide): treatments that kill microbes
Bacteriostasis: inhibiting, not killing, microbes
Figure 7.1a Understanding the
Microbial Death Curve
o Microbial death is Logarithmic
o 90% of microbial population is
killed
o Every one minute, 90% of the
population is dying until its
completely gone
Factors that affect type of Disinfectants:
Environment, temperature, presence of
biofilms (acts as a protectant), presence
of fats and proteins (protectant), time of exposure, number of microbes (the more there
are, longer it takes to kill)
Actions of Microbial Control Agents
Alteration of membrane permeability
o If the cell is leaking or exploding it will not grow
Damage to proteins (enzymes)
o Denaturation
o Reactions cannot go forward, cell will fail to grow
o Hydrogen bonds, disulfide bridges, tertiary and quaternary structure are destroyed
Damage to nucleic acids
o Damage to DNA and RNA → lethal to the cell
o Radiation, chemicals, heat
Physical Methods of Microbial Control
- Drying (desiccation) and salting (osmotic pressure)
Heat
Estimating Bacterial Numbers by Indirect Methods
Turbidity - measurement of cloudiness with a spectrophotometer
Metabolic activity - mount of metabolic product is proportional to the number of bacteria
Dry weight - bacteria are filtered, dried, and weighed; used for filamentous organisms
Chapter 7 The Control of Microbial Growth
Tables 7.5 or 7.8, and study questions at the end of the chapter
The terminology of Microbial Growth
Sepsis refers to bacterial contamination
Asepsis is the absence of significant contamination
o Aseptic surgery techniques prevent the microbial contamination of wounds
o Not sterilization, but controlling it
Sterilization : removing and destroying all microbial life
o All vegetative and non vegetative forms
o Uses sterilant
Commercial sterilization: killing Clostridium botulinum endospores from canned goods
o Getting rid of endospores that cause spoilage in food
Disinfection: destroying harmful microorganisms
o Removing from surfaces, non living tissues
Antisepsis: destroying harmful microorganisms from living tissue
Disinfectant (non living tissue) can be the same as antiseptic (on living tissue) but a
disinfectant can be harsher on living tissue
Degerming: the mechanical removal of microbes from a limited area
o Wiping off from a small area (ie swabbing alcohol when giving an injection)
Sanitization: lowering microbial counts on eating utensils to safe levels
o Ex: washing dishes, use of disinfectants
, o Not sterilizing, but decreasing microbial counts to prevent the transmission of
disease
Biocide (germicide): treatments that kill microbes
Bacteriostasis: inhibiting, not killing, microbes
Figure 7.1a Understanding the
Microbial Death Curve
o Microbial death is Logarithmic
o 90% of microbial population is
killed
o Every one minute, 90% of the
population is dying until its
completely gone
Factors that affect type of Disinfectants:
Environment, temperature, presence of
biofilms (acts as a protectant), presence
of fats and proteins (protectant), time of exposure, number of microbes (the more there
are, longer it takes to kill)
Actions of Microbial Control Agents
Alteration of membrane permeability
o If the cell is leaking or exploding it will not grow
Damage to proteins (enzymes)
o Denaturation
o Reactions cannot go forward, cell will fail to grow
o Hydrogen bonds, disulfide bridges, tertiary and quaternary structure are destroyed
Damage to nucleic acids
o Damage to DNA and RNA → lethal to the cell
o Radiation, chemicals, heat
Physical Methods of Microbial Control
- Drying (desiccation) and salting (osmotic pressure)
Heat
