Microbial Growth and Its Control Lesson 2 Flashcards
increase in number not size
Microbial Growth
Binary Fission
- Cell elongates and DNA is replicated
- Plasma membrane begins to constrict and new wall is made
- Cross-wall forms, completely separating the two DNA copies
- Cell separate
time required for a cell to divide (and its population to double)
Generation Time
Phases of Growth
- Lag Phase
- Log Phase
- Stationary Phase
- Death Phase
The Requirements for Microbial
Growth
Physical Requirements
Chemical Requirements
Physical Requirements
◦ Temperature
◦ pH
◦ Osmotic pressure
Chemical Requirements
◦ C
◦ N, S, P
◦ Trace elements
◦ O2
◦ Organic growth factors
Temperature in this range destroy most microbes, although lower temperatures take more time
60-130 C
Very slow bacterial growth
50-60 C
Rapid growth of bacteria; some may produce toxins
15-55 C
Many bacteria survive; some may grow.
-5 - 15 C
Refrigerator temperatures; may allow slow growth of spoilage bacteria, very few pathogens
0-5 C
No significant growth below freezing
0 to -30 C
PH
most bacteria– 6.5-7.5
◦ cultured bacteria produce acids that inhibit own growth; hence, buffers are used
acidophiles– even up to 1
fungi– wider range, usually 5-6
Osmotic Pressure
High osmotic pressure (hypertonic) → plasmolysis (shrinkage)
◦ adding salt can preserve food
Low osmotic pressure (hypotonic) → swelling
Extreme halophiles– can grow at high salt concentrations
- plasmolysis (shrinkage)
- adding salt can preserve food
High osmotic pressure (hypertonic)
swelling
Low osmotic pressure (hypotonic)
can grow at high salt concentrations
Extreme halophiles
- the structural backbone of living matter
- half the dry weight of bacterial cell
Carbon
2 types of C sources:
Chemoheterotrophs
Chemoautotrophs and photoautotrophs
get C from organic materials such as proteins,
carbohydrates, and lipids
Chemoheterotrophs
get C from CO2
Chemoautotrophs and photoautotrophs
Nitrogen, Sulfur, and Phosphorus
needed in the synthesis of biomolecules
elements required in small amounts e.g. Fe, Cu, Mo, Zn usually needed as cofactors
Trace Elements
Microbes that use molecular oxygen (aerobes) extract more energy from nutrients than microbes that do not use oxygen (anaerobes).
Oxygen
essential organic compounds e.g. vitamins, amino acids, pyrimidines, purines
Organic Growth Factors
thin, slimy layer encasing bacteria that adheres to a surface
Biofilm
a hydrogel, which is a complex polymer (polysaccharides, DNA and proteins)
containing many times its dry weight in water
Biofilm
allows cell-to-cell chemical communication
Biofilm
probably 1000 times more resistant to microbicides
Biofilm
e.g., Streptococcus mutans– form biofilms on teeth and gums, contributing
to dental plaque and dental caries
Biofilm
Destruction or removal of all forms of microbial life, including endospores but with the possible exception of prions.
Sterilization
Usually done by stream under pressure or a sterilizing gas such as ethylene oxide.
Sterilization
Sufficient heat treatment to kill endospores of Clostridium botulinum in canned food
Commercial Sterilization
More-resistant endospores of thermophilic bacteria may survive, but they will not germinate and grow under normal storage conditions
Commercial Sterilization
Destruction of vegetative pathogens on inanimate objects.
Disinfection
May make use of physical or chemical methods.
Disinfection
Destruction of vegetative pathogens on livinf tissue
Antisepsis
Treatment is almost always by chemical antimicrobials
Antisepsis
Removal of microbes from a limited area, such as the skin around an injection site
Degerming
Mostly a mechanical removal by soap and water or an alcohol-soaked swab
Degerming
Treatment is intended to lower microbial counts on eating and drinking utensils to safe public health levels.
Sanitization
May be done with high-temperature washing or by dipping into a chemical disinfectant
Sanitization
– kills microorganisms
Biocide/germicide
- inhibits the growth and multiplication of bacteria
Static
– bacterial contamination
Sepsis
– absence of contamination
Asepsis
– practices that exclude all organisms from contaminating media or contacting living tissues
Aseptic Technique
