Ch.6 Flashcards
Mesophiles
- Moderate temperature loving microbes
* Most pathogen’s belong to this group
Thermophiles
Heat loving microbes
Most bacteria grow best in this pH range
6.5-7.5
Mold and yeast grow best at this pH range
5.0-6.0
Osmotic Pressure
- Microorganisms require 80-90% water for growth.
* Many foods are preserved with salt, the salt draws water out of their cells and prevents growth.
Hypertonic
Cell is in a solution whose concentration of solute is higher than in the cell, The cellular water passes out through the plasma membrane to high solute concentration.
Plasmolysis
Shrinkage of the cell cytoplasm
Obligate Aerobes
Organisms that requires oxygen (O2) to live.
Facultative Anaerobe
Both aerobic and anaerobic growth.
Obligate Anaerobe
Organism that does not use oxygen (O2) to live.
Chemical requirements for microbial growth:
Carbon, Nitrogen, Sulfur Phosphorus, Trace Elements (Small mineral requirements)
Major physical requirements:
Temperature
pH
Osmotic Pressure
Quorum sensing
Cell-to-cell communication, bacteria coordinate their activity
Attracts other microbes to Biofilm
Planktonic form of biofilm
- Free swimming bacterium attaches to a surface.
- Form pillar like structures with channels between them so water can flow through, the water carries nutrients and takes away waste.
Chemically Defined
- Exact chemical composition is known
- Must contain organic growth factors that serve as a source of carbon and energy
- e. Coli
Complex medium
- Medium in which the exact chemical composition not know.
- Growth of most chemoheterotrophic organisms.
- consist of tone, beef extract, sodium chloride, agar, and water
Nutrient Broth
- Complex medium made beef extract and peptone.
* In liquid form
When agar is added to the broth it becomes:
- Nutrient Agar
* Agar itself is not a nutrient
Differential
- A solid culture medium that makes it easier to distinguish colonies of the desired organisms from other colonies growing on the same plate.
- Ex: Blood Agar
Selective Medium
- Cultural medium designed to suppress the growth of unwanted bacteria and encourage the growth of the desired microbes.
- Mannitol Salt Agar
Quadrant Streak Plate Method
- Isolation method to obtain a pure culture.
- Grows into isolated communities and then maybe transferred to a test tube of nutrient medium to form a pure culture containing only one type of bacterium.
Agar comes from?
Brown seaweed
Bacterial growth Curve
- Increase in bacterial numbers
* 4 phases
Lag Phase
- Last one hour to several days, period of little or no cell division
- Not dormant, metabolic activity, synthesis of enzymes and molecules.
- Intense activity preparation for population growth.
Log Phase (Exponential Growth Phase)
- Cells begin to divide and enter a period of growth
* Reproduction is most active by binary fission (bacteria) or mitosis (yeast),
Stationary Phase
Period of equilibrium, microbial deaths balance production of new cells.
Death Phase
- Population decreasing at a logarithmic rate.
- Cells are swimming in their own waist and have nothing to eat
- Number of deaths exceeds the number of new cells formed.
Budding
- Few species reproduce this way.
- They form a small initial outgrowth, that enlarges until it’s size approaches that of the parent cell, and then it separates.
- The time required for a sale to divide in the population to double.
- The population doubles with each generation.
- Generation time (doubling time)
* Ex.: 2^4= 16 cells
Psychrophiles/Psychrotrophs
- Cold loving microbes.
* Food microbiologists favor
