4 Microbial Growth and Control Free Online FlashCards

What are microbial growth factors?

Growth factors are organic compounds, such as vitamins or amino acids, that a microbe needs but cannot make itself.

What characterizes a mesophile?

Mesophiles grow best at moderate temperatures; many microbes associated with humans are mesophiles.

How do facultative anaerobes respond to oxygen?

Facultative anaerobes can grow both with and without oxygen.

How do halophiles differ from halotolerant microbes?

High salt or sugar can restrict growth by drawing water out of cells. Halophiles require high salt, while halotolerant microbes can withstand it.

What are the four phases of growth in a batch culture?

A batch culture commonly progresses through lag, log (exponential), stationary, and death (decline) phases.

What does generation time measure?

Generation time is the time required for a microbial population to double.

A population starts with 100 cells. How many are there after three doublings?

Three doublings give $N = 100 \times 2^3 = 800$ cells.

How does a continuous culture maintain growth conditions?

A continuous culture, such as a chemostat, adds fresh medium and removes culture at a controlled rate to help maintain growth conditions over time.

How do defined and complex media differ?

Defined media have a known chemical composition; complex media contain ingredients, such as extracts, whose exact composition varies.

What does MacConkey agar reveal about bacterial growth?

MacConkey agar selects for many Gram-negative bacteria and differentiates lactose fermenters, which form pink colonies, from nonfermenters.

What does a viable plate count estimate?

Viable plate counts estimate organisms able to form colonies under the chosen conditions and are reported as colony-forming units per milliliter (CFU/mL). A colony may arise from a cell clump.

What can turbidity estimate, and what can it not distinguish?

Turbidity is a quick, indirect estimate of cell density in a cloudy liquid culture; it does not distinguish living from dead cells.