Chapter 4 Flashcards
Two types of asexual reproduction in microbes
Binary fission and budding
Microbial growth
How often they reproduce. Not an increase in size of the individual cell
During binary fission
The bacteria cell doubled in size. Replicated chromosome. Two chromosomes attached to separate sites on the plasma membrane. Cell wall forms between the chromosomes and separates the cells producing two daughter cells.
Binary fission
Primitive form of cell division that does not use a spindle fiber apparatus. A spindle fiber apparatus made of protein filaments that move chromosomes during cell division. Bacteria do not have the structures.
Budding
A few bacteria and some eukaryotes (including yeast) may also replicate by budding. The cell forms a bubble-like growth that enlarges and separates from the parent cell
Phases of growth
Microbial lab culture typically passes through four distinct sequential phases of growth: lag phase, exponential phase, stationary phase, and death phase
Lag phase
Preparing to grow; gearing up for cell division. There’ll be no perceivable change in the number of bacteria lot of chemical reactions are taking place so when the light “turns green” they can reproduce as quickly as possible.
Exponential phase
Cell numbers increase exponentially. The phase is limited and will last 4 to 10 hours. This phase quickly uses up most of the nutrients found in the medium. Cells in this phase are very virulent, easily cause infection or disease but the cells are most susceptible to antibiotics
Stationary phase
Number of cells don't increase, but changes within cells occur. The cells become smaller and begin producing structures that help them become more resistant and are able to survive. Structures formed: Glycocalyx Endo spores Cytoplasmic inclusions
Antibiotics in the stationary phase
Antibiotics is this phase are not very effective. You must clean, drain, cut the abscess or growth away this will take the nutrients and bacteria away and fresh nutrients come in causing the leftover bacteria to be very vulnerable, more bacteria will come in and will also bring in antibiotics
Termination phase
Cells begin to die out. Death occurs exponentially, but at a low rate. Death occurs because cells have depleted intracellular ATP reserves.
What is generation time?
Length of time it takes one cell to divide into two cells. Varies between bacteria.
Why can microbes exist in many environments?
Because they are small, easily dispersed, need only small quantities of nutrients, Are diverse in their nutritional requirements.
Temperature
Bacteria can usually grow over a range of temperatures. Minimum temperature, maximum temperature, and optimum temperature
Minimum temperature
Is the lowest temperature that will permit growth and metabolism but usually at a very slow pace. Very cold temperatures do not usually denature proteins or destroy microorganisms.
Maximum temperature
Maximum temperature that permits growth and metabolism but again usually at very slow rates. Going above maximum temperatures enzymes will become denatured and metabolism will stop which destroys the cell
Optimum temperature
Typically cover the small range in which organisms metabolic processes and growth are the fastest.
Psychrophiles (cold living)
Will grow from -5°C to 20°C. they are responsible for spoiling of refrigerated and even some frozen food
Mesophiles (middle-loving)
Will grow from 20°C to 50°C. Common to be found in humans because our temperature is around 37°C
Thermophiles (heat loving)
Will grow in temperatures above 50°C to 80°C. Found in natural Hot Springs, volcanic vents etc
Hyperthermophiles
Will grow in temperatures above 80°C. Found in compost heaps and in boiling hot springs
Why does a pH of a fluid matter for any living organism?
Because enzymes work best at certain pHs
PHs of a bacteria
Maximum pH, minimum pH, and an optimum pH.
Acidophiles
Live in very acidic environments, Optimal pH is below 5.5. Example: lactobacillus
Neutrophiles
Bacteria grows best in pHs of 6 to 8. Found in WBC’s
Alkalinophiles
Optimal pH is above 8.5. Live in very alkaline environments,
Obligate Aerobe
Typically have both superoxide dismutase and catalase, and therefore can tolerate an oxygen-rich environment. Conduct a aerobic respiration and totally dependent upon oxygen without oxygen the microorganism will not grow and will die. Example: fungi
Facilitative anaerobe
Typically have superoxide dismutase and catalase. These organisms can conduct aerobic or anaerobic pathways to generate ATP. Grows best with oxygen but can reproduce without oxygen, the growth is usually slower. Example: E. coli
Obligate anaerobes
Usually lack both enzymes necessary to live in an oxygen rich environment. These organisms will conduct anaerobic pathways only. Live in places that totally lack oxygen. Cannot grow if oxygen is present. For example: deep mud
Microaerophile
Usually contain only a small amount of catalase and superoxide dismutase and can only tolerate small concentrations of oxygen. Example:found within the mucous lining of the hollow organs
Aerotolerant
Bacteria does not use oxygen, however oxygen does not harm the bacteria in this case
Hypertonic
Higher concentrations of solute outside the cell. High Salt/sugar environments will draw out the water causing the cell to dry out.
Hypotonic
Lower concentration of solute outside of the cell wall. Water will move into the cells. This will cause the cell to swell
Halotolerant
Bacteria that can tolerate moderate concentrations of salt up to 10%
Halophiles
Specialized bacteria require high levels of salt to live. 15 to 30% of salt to live and grow; to maintain cell walls; inhabit oceans or Salt Lakes
Osmophiles
Bacteria that grow in environments where sugar or solute concentrations are high.
Hydrostatic pressure
Pressure exerted by standing water. The high-pressure is necessary to keep their enzymes in the proper 3-D shape. if the enzymes lose their shape and denature the cell will die. examples: lakes, oceans, etc.
Radiation
UV rays and gamma rays can cause mutations in DNA. The rays may damage or kill microorganisms. Some bacteria have enzymes that can repair some mutations
Media
Liquid or solid material used to grow bacteria
Liquid media (broth)
Good for growing large numbers of bacteria in a short time
Solid media (ager)
A complex polysaccharide extracted from seaweed first used by Robert Koch. primarily used to provide a solid surface for bacteria to grow on
Characteristics of ager
Is not a nutrient for most bacteria, Ager melts 100°C and solidifies at 45°C, can be sterilized and can be in motility studies(helps you see if bacteria moves)
Defined (synthetic) medium
Prepared in the lab from materials of a precise or reasonably well defined composition. You know exactly how much is in it.
Complex medium
Contains certain reasonably familiar materials but varies slightly. Not really sure how much is in it but you know it’s there
Selective media
Can add nutrients to media, this will determine which bacteria will grow and which won’t
Differential
Has an ingredient that causes an observable change in the medium. Example: ager is red to begin with, and after it’s yellow due to a pH chemical reaction change
Streak plate method
- bacteria are picked up on a sterile wire loop; and the wire is moved lightly along the agar surface, depositing streaks of bacteria on the surface.
- the loop is flamed and a few bacteria are picked up from the region already deposited and streaked into a new region.
- fewer and fewer bacteria are deposited as the streaking continues
- individual organisms are deposited in the region streaked last.
- after the plate is incubated at a suitable growth temperature for the organism, small colonies appear
- the loop is used to pick up a portion of an isolated colony and transfer it to another medium for study.
- the use of aseptic technique assures that the new medium will contain organisms of a single species.
Indirect measurements
Measure a property of the mass of cells and then estimate the number of microbes
Turbidity
Hold up to light and look for cloudiness..Cloudiness is a sign of evidence growth has occurred.
Metabolic activity (3ways)
A) the rate of formation of metabolic products, such as gases or acids that a culture produces.
B) the rate of utilization of a substrate, such as oxygen, glucose, ATP
C) the rate of reduction of certain dyes.
-methylene blue becomes colorless when reduced
Direct measurements
Give more accurate measurements of numbers of microbes
Direct counts
Methods that determine total number of cells
- quick
- gives a total count, includes dead and living cells
Direct microscope count
Organisms are counted in a special glass slide under the light compound microscope
Coulter counter
- electronic counter
- rapid and accurate only if bacterial cells are the only particles present in the solution.
- dilute the solutions
Viable cell count
Determine total number if organisms that can grow under certain conditions
Standard plate count
Bacterial colonies are viewed through the magnifying glass against a colony-counting grid. Called a Quebec colony counter. Ideal number of colonies on final plate is 30-300 colonies
Filtration
A known volume of liquid or air is drawn through a membrane filter by vacuum. Great for concentrating a sample
