Microbial Growth

• Dry Weight is the fungus removed from the growth medium, filtered to remove extraneous material, and dried in a desiccator, then weighed.
• Microorganisms grow well at the temperatures that humans favor, with psychrophiles preferring cold temperatures around 0 degrees Celsius, mesophiles preferring moderate temperatures between 25-40 degrees Celsius, thermophiles preferring hot temperatures around 50-60 degrees Celsius, and hyperthermophiles preferring growth temperatures of 80 degrees Celsius or higher.
• Most bacteria grow best in a narrow pH range near neutrality, between pH 6.5 and 7.5, with very few bacteria growing at an acidic pH below about pH 4.
• Acidophiles love an acid environment.
• Most bacteria require water for growth, with hypertonic conditions having the effect of removing necessary water from the cell.
• Hypertonic conditions can cause plasmolysis, the shrinkage of cell cytoplasm.
• Extreme Halophiles require high salt concentration for growth, while Obligate Halophiles require 30% salt for growth, and Facultative Halophiles require 15% salt for growth.
• Carbon, Sulfur, Nitrogen, Phosphorus, and Trace elements such as iron, copper, molybdenum, and zinc are required for growth.
• Organic Growth Factors such as Oxygen are also required for growth.
• Aerobes use molecular oxygen, while Anaerobes do not use oxygen.
• Obligate Aerobes require oxygen to live, while Facultative Anaerobes have the ability to continue growing in the absence of oxygen.
• Filtration: Applied frequently to detection and enumeration of coliform bacteria, which are indicators of fecal contamination of food or water.
• Petroff-Hausser Cell Counter: Used for direct microscopic counting.
• Chemoautotrophic Nitrifying Bacteria: Useful when the growth of bacteria in a liquid differential medium is used to identify the microbes.
• Coulter Counter: Used for electronic cell counters.
• Most Probable Number (MPN) Method: The greater the number of bacteria in a sample, the more dilution is needed to reduce the density to the point at which no bacteria are left to grown in the tubes in a dilution series.
• Spread Plate Method: Volume of diluted culture is spread over the surface of an agar plate using a sterile glass spreader.
• Direct Microscopic Count: Measured volume of a bacterial suspension is placed within a defined area on a microscopic slide.
• Pour Plate Method: Volume of culture is pipetted into a sterile petri plate.
• Pour Plates and Spread Plates: Colonies will grow within the nutrient agar as well as on the surface of the agar plate.
• Coliform bacteria, which selectively ferment lactose to acid in water: Useful when the growth of bacteria in a liquid differential medium is used to identify the microbes.
• Plate Count: Most frequently used method of using bacterial populations, often reported as colony-forming units (CFU).
• Serial Dilution: The original inoculum is diluted several times in a process to ensure that some colony counts will be within range.
• Obligate Anaerobes are unable to use molecular oxygen for energy-yielding reactions, while Aerotolerant Anaerobes cannot use oxygen but can tolerate it.
• Binary Fission forms a new daughter cell, with the mother cell retaining its original identity through division.
• Growth Curve - The rate of cell population increase.
• Each daughter cell receives a copy of the chromosome(s) and sufficient copies of ribosomes and all other macromolecular complexed, monomers, and inorganic ions to begin life as an independent entity.
• Stationary Phase - Cells in the population grow while other die.
• Exponential or Log Phase - Cell population doubles at regular intervals.
• Complex Media - Made from digests of microbial, animal, or plant products.
• Budding Division forms a new daughter cell, with the mother cell retaining its original identity through existing organism by sprouting out.
• Viable Cell - Able to divide and form offspring, and in most cell-counting situations.
• Biofilms - An attached polysaccharide matrix containing embedded bacterial cells.
• Death Phase - Growth ceases.
• Culture Media - Laboratory cultures of microorganisms.
• During one generation, all cellular constituents increase proportionally.
• Exponential Growth - A repetitive pattern where the number of cells doubles in a constant time interval.
• Lag Phase - Growth begins only after a period of time.
• Stained Samples - Increase contrast between cells and their background.
• Microscopic Counting - A quick and easy way of estimating microbial cell numbers.