Bacterial Growth and Measurement of Growth

These flashcards cover key concepts, terms, and definitions related to bacterial growth and its measurement, as discussed in the lecture.

What are the five phases of bacterial growth?

Lag phase, Exponential phase, Stationary phase, Death phase, Long-term stationary phase.

How do bacteria primarily replicate?

Bacteria primarily replicate by binary fission.

What is generation time (g)?

The time for a cell to produce two cells or the time for a bacterial population to double in number.

What is the generation time of E. coli under optimal conditions?

Approximately 20 minutes.

What does the exponential growth phase represent?

Bacteria are growing and dividing at the maximal rate possible for the particular strain, medium, and environment.

What happens during the stationary phase?

Total viable cell numbers remain constant due to balanced cell division and death.

What is a chemostat?

A continuous culture system that maintains cells in exponential growth by providing a constant supply of one essential nutrient.

What are some applications of understanding bacterial growth?

Medical, environmental, and industrial applications including fermentation and antibiotic production.

What factors can limit bacterial growth?

Nutrient depletion, accumulation of toxic metabolic products, and limited living space.

What does a typical growth curve of bacteria illustrate?

It illustrates the five phases of growth: lag, exponential, stationary, death, and long-term stationary phases.

What is the effect of growth conditions on bacterial generation time?

Generation time varies with conditions like temperature and nutrient availability.

How is cell biomass commonly measured?

Methods include dry weight determination, wet weight determination, and spectrophotometry.

What is the significance of the lag phase?

Cells adapt to new conditions; cellular constituents are synthesized, and growth rate is initially zero.

What is the role of metabolic wastes in bacterial growth?

Accumulation of metabolic wastes can be toxic and contribute to the cessation of growth.

What is the most probable number (MPN) method?

A method to estimate the concentration of viable bacteria in a sample based on growth in multiple tubes of broth.

What are biofilms?

Aggregations of microbes in complex communities growing on surfaces and held together by extracellular polymers.

Why is it important to maintain cells in exponential growth?

It ensures uniformity in experiments and is beneficial for the production of primary metabolites.

What happens in the death phase of bacterial growth?

Population death rate is logarithmic; there's a net loss of viable cells due to nutrient deprivation or toxic build-up.

How can bacterial cell numbers be directly counted?

Using counting chambers, staining with fluorescent stains, or flow cytometry.

Which bacterial species has a generation time of approximately 12 hours?

Mycobacterium tuberculosis.

What is a common challenge in measuring bacterial growth in nature?

The complexity of interactions and environmental factors affecting growth.

What is the relationship between absorbance and bacterial growth as measured by spectrophotometry?

Absorbance is directly proportional to the biomass of cells and indirectly related to cell number.

What are some human health implications of bacterial growth?

Conditions like bacterial meningitis, cholera, food poisoning, and tetanus.

What is a significant characteristic of bacteria in stationary phase?

Cells are smaller and have a different composition compared to those in exponential phase.

Why is the exponential phase considered the most uniform?

Bacteria are growing at the maximal rate, resulting in a uniform population physiology.

What is the consequence of improper conditions during the exponential phase?

Growth occurs at a different but steady rate until limiting factors cause a transition to stationary phase.

What is the role of nutrient concentration in a chemostat?

It determines the growth rate by controlling the supply of an essential nutrient.

How are viable counts typically performed?

By serially diluting bacterial suspensions and counting colonies from various plating methods.