MODULE 6

• temperature - Most microorganisms grow well at the temperatures that humans favor.
• psychrophiles (cold-loving microbes) at 0⁰C
• mesophiles (moderate-temperature– loving microbes)

  25–40°C, are the most common type of microbe.
• thermophiles (heat-loving microbes) – 50-60⁰C
• hyperthermophiles - have an optimum growth temperature of 80°C or higher.
• extreme thermophiles – 121⁰C and above
• pH

  • refer to acidity or alkalinity of a solution.
  • Most bacteria grow best in a narrow pH range near neutrality, between pH 6.5 and 7.5.
• Acidophiles are bacteria that loves acids environment.
• Osmotic pressure - require water for growth, and their composition is 80–90% water.
• Hypertonic - whose concentration of solutes is higher than in the cell
• Plasmolysis – shrinkage of cell cytoplasm
• Extreme Halophiles – require high salt concentration
• Obligate Halophiles – require 30% of salt for growth.
• Facultative Halophiles – requires 15% of salt for growth.
• aerobes –microbes that use molecular oxygen
• anaerobes - microbes that do not use oxygen.
• Obligate aerobe - Organisms that require oxygen to live
• Facultative anaerobe - ability to continue growing in the absence of oxygen
• Obligate anaerobe - bacteria that are unable to use molecular oxygen for energy-yielding reactions
• Aerotolerant anaerobes - cannot use oxygen for growth, but they tolerate it fairly well.
• Microaerophile - they are aerobic; they do require oxygen. They grow only in oxygen concentrations lower than those in air
• Binary fission - forms a totally new daughter cell, with the mother cell retaining its original identity
• Budding division - forms a totally new daughter cell, with the mother cell retaining its original identity
• Generation time - When one cell eventually separates to form two cells, we say that one generation has occurred.
• Biofilms- an attached polysaccharide matrix containing embedded bacterial cells
• Growth - an increase in the number of cells.
• Exponential growth is a repetitive pattern where the number of cells doubles in a constant time interval.
• lag phase - growth begins only after a period of time
• exponential or log phase - cell population doubles at regular intervals
• stationary phase – cells in the population grow while others die
• death phase - growth ceases
• Defined media are prepared by adding precise amounts of pure inorganic or organic chemicals to distilled water. Exact composition is known
• Complex media are made from digests of microbial, animal, or plant products.
• Microscopic counting is a quick and easy way of estimating microbial cell numbers.
• Stained samples to increase contrast between cells and their background
• Liquid samples, counting chambers consisting of a grid with squares of known area etched on the surface of a glass slide are used.
• spread plate method - a volume (usually 0.1 ml or less) of an appropriately diluted culture is spread over the surface of an agar plate using a sterile glass spreader.
• pour plate method – a known volume (usually 0.1-1.0 ml) of culture is pipetted into a sterile Petri plate.
• Plate count - most frequently used method of measuring bacterial populations. Often reported as colony-forming units (CFU).
• Serial Dilution - to ensure that some colony counts will be within this range, the original inoculum is diluted several times in a process.