Bacterial Growth Conditions

Temperature

Because bacteria can grow and thrive in a variety of environments, optimal growth temperatures may vary significantly between species. In general, most pathogenic or commensal bacterial strains grow well at body temperature (37°C). In contrast, many environmental strains thrive at lower temperatures, often within a range of 25°C to 30°C.

Bacterial species can be categorized based on their growth temperature; these include psychrophiles (0°C to 20°C), mesophiles (25°C to 40°C), and thermophiles (45°C to 122°C). Though bacterial strains require optimal temperatures for growth and reproduction, most strains can withstand considerable drops in temperature and survive several days at 4°C. At these lower temperatures, bacterial growth and metabolism are significantly diminished. (See: NOTE 2)

NOTE 2
Regularly calibrate the temperature control system of incubators. Use an alarm system when possible to warn against temperature increases above the optimum setting.

Glossary

Aerobe. Organisms that require oxygen for survival. Bacterial aerobes use oxygen as the terminal electron acceptor during respiration.

Aerotolerant anaerobes. Organisms that cannot use oxygen, nor are affected by its presence.

Anaerobes. Organisms that do not require oxygen for survival. These organisms use inorganic compounds as the terminal electron acceptor during respiration.

Complex medium. An undefined medium containing unknown quantities of reagents. These media contain complex ingredients, such as yeast extract and peptone, which contain a combination of compounds in unknown proportions.

Cryopreservation. Ultra-low temperature storage of cells, tissues, embryos, or seeds. This storage is usually carried out using temperatures below -100°C.

Defibrinated blood. Whole blood from which fibrin has been separated during the clotting process.

Defined medium. Media with known proportions of all reagents. These media consist of a defined carbon and nitrogen source.

Desiccant. A hygroscopic substance that induces or sustains a state of dryness in its local vicinity in a sealed container.

Desorption. The phenomenon where a substance is released from or through a surface.

Enrichment medium. These media contain the nutrients required to support the growth of a wide array of microorganisms.

Facultative anaerobe. An organism that can survive in the presence and absence of oxygen. If given the choice, these organisms prefer the use of oxygen as it has the highest reduction potential of all terminal electron acceptors.

Fastidious. Having to do with microorganisms that have complex nutritional needs and require growth on enriched media.

Hypotonic. An environment where the water concentration is greater and solute concentration is lower on the outside of a cell. In this environment, water flows into the cell.

Isotonic. An environment where both the water and solute concentrations are the same on the inside and outside of a cell. In this environment, water flows in and out of a cell at an equal rate.

Lyophilization. A process which extracts water molecules from microbial cultures so that products remain stable and easy to store. This storage is usually carried out under low-oxygen, low-moisture conditions at 4°C.

Mesophile. An organism that grows best at moderate temperatures, between 25°C to 40°C.

Microaerophile. An organism that requires oxygen for respiration, however in lower levels than found in the atmosphere.

Obligate anaerobe. An organism that cannot survive and are often killed by the presence of oxygen.

Osmolarity. The concentration of a solution in terms of osmoles. Osmosis is the diffusion of water across a membrane from an area of higher water concentration (lower solute concentration) to lower water concentration (higher solute concentration).

Psychrophile. An extremophilic organism that is capable of growth in cold temperatures ranging from 0°C to 20°C.

Ribotyping. A method of identification involving the fingerprinting of genomic DNA restriction fragments.

Selective medium. Media used for the growth of specific microorganisms. These media are often supplemented with reagents, such as antibiotics, that prevent the growth of other microorganisms.

Thermophile. An extremophilic organism that thrives a high temperatures ranging from 45°C to 122°C.