Module 5 Microbial Growth

Psychrophiles

Cold-loving microbes that grow at 0°C.

Mesophiles

Moderate-temperature-loving microbes that grow at 25-40°C.

Extreme thermophiles

Microbes that grow at 121°C and above.

Acidophiles

Bacteria that thrive in acidic environments.

Osmotic pressure

The pressure exerted on a cell due to differences in solute concentration.

Hypertonic

A solution with a higher solute concentration than the cell.

Plasmolysis

The shrinkage of cell cytoplasm due to high osmotic pressure.

Halophiles

Microorganisms that can grow in or tolerate saline conditions.

Extreme Halophiles

Halophiles that require high salt concentrations.

Obligate Halophiles

Halophiles that require 30% salt for growth.

Facultative Halophiles

Halophiles that require 15% salt for growth.

Carbon

A chemical requirement for microbial growth.

Trace elements

Elements such as iron, copper, molybdenum, and zinc that are required in small amounts for microbial growth.

Organic Growth factors

Substances required by some microorganisms for growth that cannot be synthesized by the organism.

Oxygen

A chemical requirement for microbial growth.

Aerobes

Microbes that use molecular oxygen for growth.

Anaerobes

Microbes that do not use oxygen for growth.

Obligate aerobe

Organisms that require oxygen to live.

Facultative anaerobe

Organisms that can continue growing in the absence of oxygen.

Obligate anaerobe

Bacteria that are unable to use molecular oxygen for energy-yielding reactions.

Aerotolerant anaerobes

Microbes that cannot use oxygen for growth but can tolerate its presence.

Microaerophile

Microbes that require oxygen but only in lower concentrations than those in air.

Binary fission

A method of cell division in which a mother cell divides to form two daughter cells.

Budding division

A method of cell division in which progeny develops from the generative tissue or cell of the parent organism.

Generation time

The time it takes for one cell to divide and form two cells.

Biofilms

Attached polysaccharide matrices containing embedded bacterial cells.

Growth

An increase in the number of cells.

Exponential growth

A pattern where the number of cells doubles in a constant time interval.

Lag phase

The phase of growth where there is a delay before growth begins.

Exponential or log phase

The phase of growth where cell population doubles at regular intervals.

Stationary phase

The phase of growth where cells in the population grow while others die.

Death phase

The phase of growth where growth ceases.

Continuous culture

A type of open system used to control specific growth rate and cell density independently.

Chemostat

The most common type of continuous culture.

Defined media

Culture media prepared by adding precise amounts of pure inorganic or organic chemicals to distilled water.

Complex media

Culture media made from digests of microbial, animal, or plant products.

Total Cell Count

Estimating microbial cell numbers through microscopic counting.

Viable cell

A cell that is able to divide and form offspring.

Spread plate method

A method of viable plate count where a diluted culture is spread over the surface of an agar plate.

Pour plate method

A method of viable plate count where a known volume of culture is pipetted into a sterile Petri plate.

Plate count

The most frequently used method of measuring bacterial populations, often reported as colony-forming units (CFU).

Serial Dilution

A process of diluting the original inoculum several times to ensure that some colony counts will be within a measurable range.

Pour plates and spread plates

Pour plate method allows colonies to grow within the nutrient agar as well as on the surface of the agar plate, while spread plate method positions all the colonies on the surface and avoids contact between the cells and melted agar.

Filtration

A method applied frequently to detect and enumerate coliform bacteria, which are indicators of fecal contamination of food or water.