Ch.9

Microbial Growth

An increase in the number of cells, not the size of individual cells, typically occurs through cell division by binary fission in prokaryotes.

Lag Phase

The initial phase in the growth curve where cells are adjusting to the environment and no cell division occurs.

Log (Exponential) Phase

A phase of rapid cell division and growth where cells are most sensitive to antibiotics.

Stationary Phase

A phase in the growth curve where nutrients become limited and waste products accumulate, leading to a balance between cell division and death.

Death (Decline) Phase

The final phase in the growth curve where cells die due to depletion of nutrients and accumulation of toxic wastes.

Psychrophiles

Microorganisms that thrive in cold environments.

Mesophiles

Microorganisms that prefer moderate temperatures; many human pathogens are classified as mesophiles.

Thermophiles

Microorganisms that thrive in warm to hot environments.

Hyperthermophiles

Microorganisms that thrive in extremely hot environments, such as hydrothermal vents.

Optimal Growth Temperature

The temperature at which a microorganism grows best.

Acidophiles

Microorganisms that prefer acidic environments, typically with a pH less than 5.5.

Neutrophiles

Microorganisms that prefer neutral pH levels, usually between pH 6 and 8.

Alkaliphiles

Microorganisms that thrive in basic environments, often with a pH greater than 8.5.

Obligate Aerobes

Microorganisms that require oxygen for growth.

Obligate Anaerobes

Microorganisms that cannot grow in the presence of oxygen.

Facultative Anaerobes

Microorganisms that can grow with or without oxygen.

Aerotolerant Anaerobes

Microorganisms that tolerate oxygen but do not use it for growth.

Microaerophiles

Microorganisms that require oxygen but at lower concentrations than present in the atmosphere.

Halophiles

Salt-loving microorganisms that thrive in high salt concentrations.

Xerophiles

Microorganisms that are adapted to grow in dry environments.

Plate Counts

A direct method for measuring microbial growth by counting colonies on agar plates.

Turbidity

An indirect method of measuring microbial growth by measuring the cloudiness of a culture using a spectrophotometer.

Essential Nutrients

Nutrients required for microbial growth, including macronutrients and micronutrients.

Macronutrients

Nutrients required in large quantities for microbial growth, such as Carbon, Nitrogen, and Phosphorus.

Micronutrients

Nutrients required in trace amounts, often serving as cofactors for enzymes.

Selective Media

Nutrient media that encourages the growth of specific microorganisms while inhibiting the growth of others.

Differential Media

Nutrient media that allows distinction between different microorganisms based on observable characteristics.